.emacs.d/elpa/dash-2.16.0/dash.info

This is dash.info, produced by makeinfo version 6.5 from dash.texi.

This manual is for ‘dash.el’ version 2.12.1.

   Copyright © 2012-2015 Magnar Sveen

     This program is free software; you can redistribute it and/or
     modify it under the terms of the GNU General Public License as
     published by the Free Software Foundation, either version 3 of the
     License, or (at your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see
     <http://www.gnu.org/licenses/>.
INFO-DIR-SECTION Emacs
START-INFO-DIR-ENTRY
* Dash: (dash.info). A modern list library for GNU Emacs
END-INFO-DIR-ENTRY


File: dash.info,  Node: Top,  Next: Installation,  Up: (dir)

dash
****

This manual is for ‘dash.el’ version 2.12.1.

   Copyright © 2012-2015 Magnar Sveen

     This program is free software; you can redistribute it and/or
     modify it under the terms of the GNU General Public License as
     published by the Free Software Foundation, either version 3 of the
     License, or (at your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see
     <http://www.gnu.org/licenses/>.

* Menu:

* Installation::
* Functions::
* Development::
* Index::

— The Detailed Node Listing —

Installation

* Using in a package::
* Syntax highlighting of dash functions::

Functions

* Maps::
* Sublist selection::
* List to list::
* Reductions::
* Unfolding::
* Predicates::
* Partitioning::
* Indexing::
* Set operations::
* Other list operations::
* Tree operations::
* Threading macros::
* Binding::
* Side-effects::
* Destructive operations::
* Function combinators::

Development

* Contribute::          How to contribute
* Changes::             List of significant changes by version
* Contributors::        List of contributors


File: dash.info,  Node: Installation,  Next: Functions,  Prev: Top,  Up: Top

1 Installation
**************

It’s available on marmalade (http://marmalade-repo.org/) and Melpa
(https://melpa.org/); use ‘M-x package-install’:

‘M-x package-install <RET> dash’
     Install the dash library.

‘M-x package-install <RET> dash-functional’
     Optional, if you want the function combinators.

   Alternatively, you can just dump dash.el or dash-functional.el in
your load path somewhere.

* Menu:

* Using in a package::
* Syntax highlighting of dash functions::


File: dash.info,  Node: Using in a package,  Next: Syntax highlighting of dash functions,  Up: Installation

1.1 Using in a package
======================

Add this to the big comment block at the top:

     ;; Package-Requires: ((dash "2.12.1"))

To get function combinators:

     ;; Package-Requires: ((dash "2.12.1") (dash-functional "1.2.0") (emacs "24"))


File: dash.info,  Node: Syntax highlighting of dash functions,  Prev: Using in a package,  Up: Installation

1.2 Syntax highlighting of dash functions
=========================================

Font lock of dash functions in emacs lisp buffers is now optional.
Include this in your emacs settings to get syntax highlighting:

     (eval-after-load 'dash '(dash-enable-font-lock))


File: dash.info,  Node: Functions,  Next: Development,  Prev: Installation,  Up: Top

2 Functions
***********

This chapter contains reference documentation for the dash application
programming interface (API). All functions and constructs in the library
are prefixed with a dash (-).

   There are also anaphoric versions of functions where that makes
sense, prefixed with two dashes instead of one.

   For instance, while ‘-map’ takes a function to map over the list, one
can also use the anaphoric form with double dashes - which will then be
executed with ‘it’ exposed as the list item.  Here’s an example:

     (-map (lambda (n) (* n n)) '(1 2 3 4)) ;; normal version

     (--map (* it it) '(1 2 3 4)) ;; anaphoric version

Of course, the original can also be written like

     (defun square (n) (* n n))

     (-map 'square '(1 2 3 4))

which demonstrates the usefulness of both versions.

* Menu:

* Maps::
* Sublist selection::
* List to list::
* Reductions::
* Unfolding::
* Predicates::
* Partitioning::
* Indexing::
* Set operations::
* Other list operations::
* Tree operations::
* Threading macros::
* Binding::
* Side-effects::
* Destructive operations::
* Function combinators::


File: dash.info,  Node: Maps,  Next: Sublist selection,  Up: Functions

2.1 Maps
========

Functions in this category take a transforming function, which is then
applied sequentially to each or selected elements of the input list.
The results are collected in order and returned as new list.

 -- Function: -map (fn list)
     Return a new list consisting of the result of applying FN to the
     items in LIST.

          (-map (lambda (num) (* num num)) '(1 2 3 4))
              ⇒ '(1 4 9 16)
          (-map 'square '(1 2 3 4))
              ⇒ '(1 4 9 16)
          (--map (* it it) '(1 2 3 4))
              ⇒ '(1 4 9 16)

 -- Function: -map-when (pred rep list)
     Return a new list where the elements in LIST that do not match the
     PRED function are unchanged, and where the elements in LIST that do
     match the PRED function are mapped through the REP function.

     Alias: ‘-replace-where’

     See also: ‘-update-at’ (*note -update-at::)

          (-map-when 'even? 'square '(1 2 3 4))
              ⇒ '(1 4 3 16)
          (--map-when (> it 2) (* it it) '(1 2 3 4))
              ⇒ '(1 2 9 16)
          (--map-when (= it 2) 17 '(1 2 3 4))
              ⇒ '(1 17 3 4)

 -- Function: -map-first (pred rep list)
     Replace first item in LIST satisfying PRED with result of REP
     called on this item.

     See also: ‘-map-when’ (*note -map-when::), ‘-replace-first’ (*note
     -replace-first::)

          (-map-first 'even? 'square '(1 2 3 4))
              ⇒ '(1 4 3 4)
          (--map-first (> it 2) (* it it) '(1 2 3 4))
              ⇒ '(1 2 9 4)
          (--map-first (= it 2) 17 '(1 2 3 2))
              ⇒ '(1 17 3 2)

 -- Function: -map-last (pred rep list)
     Replace last item in LIST satisfying PRED with result of REP called
     on this item.

     See also: ‘-map-when’ (*note -map-when::), ‘-replace-last’ (*note
     -replace-last::)

          (-map-last 'even? 'square '(1 2 3 4))
              ⇒ '(1 2 3 16)
          (--map-last (> it 2) (* it it) '(1 2 3 4))
              ⇒ '(1 2 3 16)
          (--map-last (= it 2) 17 '(1 2 3 2))
              ⇒ '(1 2 3 17)

 -- Function: -map-indexed (fn list)
     Return a new list consisting of the result of (FN index item) for
     each item in LIST.

     In the anaphoric form ‘--map-indexed’, the index is exposed as
     symbol ‘it-index’.

     See also: ‘-each-indexed’ (*note -each-indexed::).

          (-map-indexed (lambda (index item) (- item index)) '(1 2 3 4))
              ⇒ '(1 1 1 1)
          (--map-indexed (- it it-index) '(1 2 3 4))
              ⇒ '(1 1 1 1)

 -- Function: -annotate (fn list)
     Return a list of cons cells where each cell is FN applied to each
     element of LIST paired with the unmodified element of LIST.

          (-annotate '1+ '(1 2 3))
              ⇒ '((2 . 1) (3 . 2) (4 . 3))
          (-annotate 'length '(("h" "e" "l" "l" "o") ("hello" "world")))
              ⇒ '((5 "h" "e" "l" "l" "o") (2 "hello" "world"))
          (--annotate (< 1 it) '(0 1 2 3))
              ⇒ '((nil . 0) (nil . 1) (t . 2) (t . 3))

 -- Function: -splice (pred fun list)
     Splice lists generated by FUN in place of elements matching PRED in
     LIST.

     FUN takes the element matching PRED as input.

     This function can be used as replacement for ‘,@’ in case you need
     to splice several lists at marked positions (for example with
     keywords).

     See also: ‘-splice-list’ (*note -splice-list::), ‘-insert-at’
     (*note -insert-at::)

          (-splice 'even? (lambda (x) (list x x)) '(1 2 3 4))
              ⇒ '(1 2 2 3 4 4)
          (--splice 't (list it it) '(1 2 3 4))
              ⇒ '(1 1 2 2 3 3 4 4)
          (--splice (equal it :magic) '((list of) (magical) (code)) '((foo) (bar) :magic (baz)))
              ⇒ '((foo) (bar) (list of) (magical) (code) (baz))

 -- Function: -splice-list (pred new-list list)
     Splice NEW-LIST in place of elements matching PRED in LIST.

     See also: ‘-splice’ (*note -splice::), ‘-insert-at’ (*note
     -insert-at::)

          (-splice-list 'keywordp '(a b c) '(1 :foo 2))
              ⇒ '(1 a b c 2)
          (-splice-list 'keywordp nil '(1 :foo 2))
              ⇒ '(1 2)
          (--splice-list (keywordp it) '(a b c) '(1 :foo 2))
              ⇒ '(1 a b c 2)

 -- Function: -mapcat (fn list)
     Return the concatenation of the result of mapping FN over LIST.
     Thus function FN should return a list.

          (-mapcat 'list '(1 2 3))
              ⇒ '(1 2 3)
          (-mapcat (lambda (item) (list 0 item)) '(1 2 3))
              ⇒ '(0 1 0 2 0 3)
          (--mapcat (list 0 it) '(1 2 3))
              ⇒ '(0 1 0 2 0 3)

 -- Function: -copy (arg)
     Create a shallow copy of LIST.

     (fn LIST)

          (-copy '(1 2 3))
              ⇒ '(1 2 3)
          (let ((a '(1 2 3))) (eq a (-copy a)))
              ⇒ nil


File: dash.info,  Node: Sublist selection,  Next: List to list,  Prev: Maps,  Up: Functions

2.2 Sublist selection
=====================

Functions returning a sublist of the original list.

 -- Function: -filter (pred list)
     Return a new list of the items in LIST for which PRED returns a
     non-nil value.

     Alias: ‘-select’

     See also: ‘-keep’ (*note -keep::), ‘-remove’ (*note -remove::).

          (-filter (lambda (num) (= 0 (% num 2))) '(1 2 3 4))
              ⇒ '(2 4)
          (-filter 'even? '(1 2 3 4))
              ⇒ '(2 4)
          (--filter (= 0 (% it 2)) '(1 2 3 4))
              ⇒ '(2 4)

 -- Function: -remove (pred list)
     Return a new list of the items in LIST for which PRED returns nil.

     Alias: ‘-reject’

     See also: ‘-filter’ (*note -filter::).

          (-remove (lambda (num) (= 0 (% num 2))) '(1 2 3 4))
              ⇒ '(1 3)
          (-remove 'even? '(1 2 3 4))
              ⇒ '(1 3)
          (--remove (= 0 (% it 2)) '(1 2 3 4))
              ⇒ '(1 3)

 -- Function: -remove-first (pred list)
     Return a new list with the first item matching PRED removed.

     Alias: ‘-reject-first’

     See also: ‘-remove’ (*note -remove::), ‘-map-first’ (*note
     -map-first::)

          (-remove-first 'even? '(1 3 5 4 7 8 10))
              ⇒ '(1 3 5 7 8 10)
          (-remove-first 'stringp '(1 2 "first" "second" "third"))
              ⇒ '(1 2 "second" "third")
          (--remove-first (> it 3) '(1 2 3 4 5 6 7 8 9 10))
              ⇒ '(1 2 3 5 6 7 8 9 10)

 -- Function: -remove-last (pred list)
     Return a new list with the last item matching PRED removed.

     Alias: ‘-reject-last’

     See also: ‘-remove’ (*note -remove::), ‘-map-last’ (*note
     -map-last::)

          (-remove-last 'even? '(1 3 5 4 7 8 10 11))
              ⇒ '(1 3 5 4 7 8 11)
          (-remove-last 'stringp '(1 2 "last" "second" "third"))
              ⇒ '(1 2 "last" "second")
          (--remove-last (> it 3) '(1 2 3 4 5 6 7 8 9 10))
              ⇒ '(1 2 3 4 5 6 7 8 9)

 -- Function: -remove-item (item list)
     Remove all occurences of ITEM from LIST.

     Comparison is done with ‘equal’.

          (-remove-item 3 '(1 2 3 2 3 4 5 3))
              ⇒ '(1 2 2 4 5)
          (-remove-item 'foo '(foo bar baz foo))
              ⇒ '(bar baz)
          (-remove-item "bob" '("alice" "bob" "eve" "bob" "dave"))
              ⇒ '("alice" "eve" "dave")

 -- Function: -non-nil (list)
     Return all non-nil elements of LIST.

          (-non-nil '(1 nil 2 nil nil 3 4 nil 5 nil))
              ⇒ '(1 2 3 4 5)

 -- Function: -slice (list from &optional to step)
     Return copy of LIST, starting from index FROM to index TO.

     FROM or TO may be negative.  These values are then interpreted
     modulo the length of the list.

     If STEP is a number, only each STEPth item in the resulting section
     is returned.  Defaults to 1.

          (-slice '(1 2 3 4 5) 1)
              ⇒ '(2 3 4 5)
          (-slice '(1 2 3 4 5) 0 3)
              ⇒ '(1 2 3)
          (-slice '(1 2 3 4 5 6 7 8 9) 1 -1 2)
              ⇒ '(2 4 6 8)

 -- Function: -take (n list)
     Return a new list of the first N items in LIST, or all items if
     there are fewer than N.

     See also: ‘-take-last’ (*note -take-last::)

          (-take 3 '(1 2 3 4 5))
              ⇒ '(1 2 3)
          (-take 17 '(1 2 3 4 5))
              ⇒ '(1 2 3 4 5)

 -- Function: -take-last (n list)
     Return the last N items of LIST in order.

     See also: ‘-take’ (*note -take::)

          (-take-last 3 '(1 2 3 4 5))
              ⇒ '(3 4 5)
          (-take-last 17 '(1 2 3 4 5))
              ⇒ '(1 2 3 4 5)
          (-take-last 1 '(1 2 3 4 5))
              ⇒ '(5)

 -- Function: -drop (n list)
     Return the tail of LIST without the first N items.

     See also: ‘-drop-last’ (*note -drop-last::)

     (fn N LIST)

          (-drop 3 '(1 2 3 4 5))
              ⇒ '(4 5)
          (-drop 17 '(1 2 3 4 5))
              ⇒ '()

 -- Function: -drop-last (n list)
     Remove the last N items of LIST and return a copy.

     See also: ‘-drop’ (*note -drop::)

          (-drop-last 3 '(1 2 3 4 5))
              ⇒ '(1 2)
          (-drop-last 17 '(1 2 3 4 5))
              ⇒ '()

 -- Function: -take-while (pred list)
     Return a new list of successive items from LIST while (PRED item)
     returns a non-nil value.

          (-take-while 'even? '(1 2 3 4))
              ⇒ '()
          (-take-while 'even? '(2 4 5 6))
              ⇒ '(2 4)
          (--take-while (< it 4) '(1 2 3 4 3 2 1))
              ⇒ '(1 2 3)

 -- Function: -drop-while (pred list)
     Return the tail of LIST starting from the first item for which
     (PRED item) returns nil.

          (-drop-while 'even? '(1 2 3 4))
              ⇒ '(1 2 3 4)
          (-drop-while 'even? '(2 4 5 6))
              ⇒ '(5 6)
          (--drop-while (< it 4) '(1 2 3 4 3 2 1))
              ⇒ '(4 3 2 1)

 -- Function: -select-by-indices (indices list)
     Return a list whose elements are elements from LIST selected as
     ‘(nth i list)‘ for all i from INDICES.

          (-select-by-indices '(4 10 2 3 6) '("v" "e" "l" "o" "c" "i" "r" "a" "p" "t" "o" "r"))
              ⇒ '("c" "o" "l" "o" "r")
          (-select-by-indices '(2 1 0) '("a" "b" "c"))
              ⇒ '("c" "b" "a")
          (-select-by-indices '(0 1 2 0 1 3 3 1) '("f" "a" "r" "l"))
              ⇒ '("f" "a" "r" "f" "a" "l" "l" "a")

 -- Function: -select-columns (columns table)
     Select COLUMNS from TABLE.

     TABLE is a list of lists where each element represents one row.  It
     is assumed each row has the same length.

     Each row is transformed such that only the specified COLUMNS are
     selected.

     See also: ‘-select-column’ (*note -select-column::),
     ‘-select-by-indices’ (*note -select-by-indices::)

          (-select-columns '(0 2) '((1 2 3) (a b c) (:a :b :c)))
              ⇒ '((1 3) (a c) (:a :c))
          (-select-columns '(1) '((1 2 3) (a b c) (:a :b :c)))
              ⇒ '((2) (b) (:b))
          (-select-columns nil '((1 2 3) (a b c) (:a :b :c)))
              ⇒ '(nil nil nil)

 -- Function: -select-column (column table)
     Select COLUMN from TABLE.

     TABLE is a list of lists where each element represents one row.  It
     is assumed each row has the same length.

     The single selected column is returned as a list.

     See also: ‘-select-columns’ (*note -select-columns::),
     ‘-select-by-indices’ (*note -select-by-indices::)

          (-select-column 1 '((1 2 3) (a b c) (:a :b :c)))
              ⇒ '(2 b :b)


File: dash.info,  Node: List to list,  Next: Reductions,  Prev: Sublist selection,  Up: Functions

2.3 List to list
================

Functions returning a modified copy of the input list.

 -- Function: -keep (fn list)
     Return a new list of the non-nil results of applying FN to the
     items in LIST.

     If you want to select the original items satisfying a predicate use
     ‘-filter’ (*note -filter::).

          (-keep 'cdr '((1 2 3) (4 5) (6)))
              ⇒ '((2 3) (5))
          (-keep (lambda (num) (when (> num 3) (* 10 num))) '(1 2 3 4 5 6))
              ⇒ '(40 50 60)
          (--keep (when (> it 3) (* 10 it)) '(1 2 3 4 5 6))
              ⇒ '(40 50 60)

 -- Function: -concat (&rest lists)
     Return a new list with the concatenation of the elements in the
     supplied LISTS.

          (-concat '(1))
              ⇒ '(1)
          (-concat '(1) '(2))
              ⇒ '(1 2)
          (-concat '(1) '(2 3) '(4))
              ⇒ '(1 2 3 4)

 -- Function: -flatten (l)
     Take a nested list L and return its contents as a single, flat
     list.

     Note that because ‘nil’ represents a list of zero elements (an
     empty list), any mention of nil in L will disappear after
     flattening.  If you need to preserve nils, consider ‘-flatten-n’
     (*note -flatten-n::) or map them to some unique symbol and then map
     them back.

     Conses of two atoms are considered "terminals", that is, they
     aren’t flattened further.

     See also: ‘-flatten-n’ (*note -flatten-n::)

          (-flatten '((1)))
              ⇒ '(1)
          (-flatten '((1 (2 3) (((4 (5)))))))
              ⇒ '(1 2 3 4 5)
          (-flatten '(1 2 (3 . 4)))
              ⇒ '(1 2 (3 . 4))

 -- Function: -flatten-n (num list)
     Flatten NUM levels of a nested LIST.

     See also: ‘-flatten’ (*note -flatten::)

          (-flatten-n 1 '((1 2) ((3 4) ((5 6)))))
              ⇒ '(1 2 (3 4) ((5 6)))
          (-flatten-n 2 '((1 2) ((3 4) ((5 6)))))
              ⇒ '(1 2 3 4 (5 6))
          (-flatten-n 3 '((1 2) ((3 4) ((5 6)))))
              ⇒ '(1 2 3 4 5 6)

 -- Function: -replace (old new list)
     Replace all OLD items in LIST with NEW.

     Elements are compared using ‘equal’.

     See also: ‘-replace-at’ (*note -replace-at::)

          (-replace 1 "1" '(1 2 3 4 3 2 1))
              ⇒ '("1" 2 3 4 3 2 "1")
          (-replace "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo"))
              ⇒ '("a" "nice" "bar" "sentence" "about" "bar")
          (-replace 1 2 nil)
              ⇒ nil

 -- Function: -replace-first (old new list)
     Replace the first occurence of OLD with NEW in LIST.

     Elements are compared using ‘equal’.

     See also: ‘-map-first’ (*note -map-first::)

          (-replace-first 1 "1" '(1 2 3 4 3 2 1))
              ⇒ '("1" 2 3 4 3 2 1)
          (-replace-first "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo"))
              ⇒ '("a" "nice" "bar" "sentence" "about" "foo")
          (-replace-first 1 2 nil)
              ⇒ nil

 -- Function: -replace-last (old new list)
     Replace the last occurence of OLD with NEW in LIST.

     Elements are compared using ‘equal’.

     See also: ‘-map-last’ (*note -map-last::)

          (-replace-last 1 "1" '(1 2 3 4 3 2 1))
              ⇒ '(1 2 3 4 3 2 "1")
          (-replace-last "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo"))
              ⇒ '("a" "nice" "foo" "sentence" "about" "bar")
          (-replace-last 1 2 nil)
              ⇒ nil

 -- Function: -insert-at (n x list)
     Return a list with X inserted into LIST at position N.

     See also: ‘-splice’ (*note -splice::), ‘-splice-list’ (*note
     -splice-list::)

          (-insert-at 1 'x '(a b c))
              ⇒ '(a x b c)
          (-insert-at 12 'x '(a b c))
              ⇒ '(a b c x)

 -- Function: -replace-at (n x list)
     Return a list with element at Nth position in LIST replaced with X.

     See also: ‘-replace’ (*note -replace::)

          (-replace-at 0 9 '(0 1 2 3 4 5))
              ⇒ '(9 1 2 3 4 5)
          (-replace-at 1 9 '(0 1 2 3 4 5))
              ⇒ '(0 9 2 3 4 5)
          (-replace-at 4 9 '(0 1 2 3 4 5))
              ⇒ '(0 1 2 3 9 5)

 -- Function: -update-at (n func list)
     Return a list with element at Nth position in LIST replaced with
     ‘(func (nth n list))‘.

     See also: ‘-map-when’ (*note -map-when::)

          (-update-at 0 (lambda (x) (+ x 9)) '(0 1 2 3 4 5))
              ⇒ '(9 1 2 3 4 5)
          (-update-at 1 (lambda (x) (+ x 8)) '(0 1 2 3 4 5))
              ⇒ '(0 9 2 3 4 5)
          (--update-at 2 (length it) '("foo" "bar" "baz" "quux"))
              ⇒ '("foo" "bar" 3 "quux")

 -- Function: -remove-at (n list)
     Return a list with element at Nth position in LIST removed.

     See also: ‘-remove-at-indices’ (*note -remove-at-indices::),
     ‘-remove’ (*note -remove::)

          (-remove-at 0 '("0" "1" "2" "3" "4" "5"))
              ⇒ '("1" "2" "3" "4" "5")
          (-remove-at 1 '("0" "1" "2" "3" "4" "5"))
              ⇒ '("0" "2" "3" "4" "5")
          (-remove-at 2 '("0" "1" "2" "3" "4" "5"))
              ⇒ '("0" "1" "3" "4" "5")

 -- Function: -remove-at-indices (indices list)
     Return a list whose elements are elements from LIST without
     elements selected as ‘(nth i list)‘ for all i from INDICES.

     See also: ‘-remove-at’ (*note -remove-at::), ‘-remove’ (*note
     -remove::)

          (-remove-at-indices '(0) '("0" "1" "2" "3" "4" "5"))
              ⇒ '("1" "2" "3" "4" "5")
          (-remove-at-indices '(0 2 4) '("0" "1" "2" "3" "4" "5"))
              ⇒ '("1" "3" "5")
          (-remove-at-indices '(0 5) '("0" "1" "2" "3" "4" "5"))
              ⇒ '("1" "2" "3" "4")


File: dash.info,  Node: Reductions,  Next: Unfolding,  Prev: List to list,  Up: Functions

2.4 Reductions
==============

Functions reducing lists into single value.

 -- Function: -reduce-from (fn initial-value list)
     Return the result of applying FN to INITIAL-VALUE and the first
     item in LIST, then applying FN to that result and the 2nd item,
     etc.  If LIST contains no items, return INITIAL-VALUE and do not
     call FN.

     In the anaphoric form ‘--reduce-from’, the accumulated value is
     exposed as symbol ‘acc’.

     See also: ‘-reduce’ (*note -reduce::), ‘-reduce-r’ (*note
     -reduce-r::)

          (-reduce-from '- 10 '(1 2 3))
              ⇒ 4
          (-reduce-from (lambda (memo item) (format "(%s - %d)" memo item)) "10" '(1 2 3))
              ⇒ "(((10 - 1) - 2) - 3)"
          (--reduce-from (concat acc " " it) "START" '("a" "b" "c"))
              ⇒ "START a b c"

 -- Function: -reduce-r-from (fn initial-value list)
     Replace conses with FN, nil with INITIAL-VALUE and evaluate the
     resulting expression.  If LIST is empty, INITIAL-VALUE is returned
     and FN is not called.

     Note: this function works the same as ‘-reduce-from’ (*note
     -reduce-from::) but the operation associates from right instead of
     from left.

     See also: ‘-reduce-r’ (*note -reduce-r::), ‘-reduce’ (*note
     -reduce::)

          (-reduce-r-from '- 10 '(1 2 3))
              ⇒ -8
          (-reduce-r-from (lambda (item memo) (format "(%d - %s)" item memo)) "10" '(1 2 3))
              ⇒ "(1 - (2 - (3 - 10)))"
          (--reduce-r-from (concat it " " acc) "END" '("a" "b" "c"))
              ⇒ "a b c END"

 -- Function: -reduce (fn list)
     Return the result of applying FN to the first 2 items in LIST, then
     applying FN to that result and the 3rd item, etc.  If LIST contains
     no items, return the result of calling FN with no arguments.  If
     LIST contains a single item, return that item and do not call FN.

     In the anaphoric form ‘--reduce’, the accumulated value is exposed
     as symbol ‘acc’.

     See also: ‘-reduce-from’ (*note -reduce-from::), ‘-reduce-r’ (*note
     -reduce-r::)

          (-reduce '- '(1 2 3 4))
              ⇒ -8
          (-reduce 'list '(1 2 3 4))
              ⇒ '(((1 2) 3) 4)
          (--reduce (format "%s-%d" acc it) '(1 2 3))
              ⇒ "1-2-3"

 -- Function: -reduce-r (fn list)
     Replace conses with FN and evaluate the resulting expression.  The
     final nil is ignored.  If LIST contains no items, return the result
     of calling FN with no arguments.  If LIST contains a single item,
     return that item and do not call FN.

     The first argument of FN is the new item, the second is the
     accumulated value.

     Note: this function works the same as ‘-reduce’ (*note -reduce::)
     but the operation associates from right instead of from left.

     See also: ‘-reduce-r-from’ (*note -reduce-r-from::), ‘-reduce’
     (*note -reduce::)

          (-reduce-r '- '(1 2 3 4))
              ⇒ -2
          (-reduce-r (lambda (item memo) (format "%s-%d" memo item)) '(1 2 3))
              ⇒ "3-2-1"
          (--reduce-r (format "%s-%d" acc it) '(1 2 3))
              ⇒ "3-2-1"

 -- Function: -reductions-from (fn init list)
     Return a list of the intermediate values of the reduction.

     See ‘-reduce-from’ (*note -reduce-from::) for explanation of the
     arguments.

     See also: ‘-reductions’ (*note -reductions::), ‘-reductions-r’
     (*note -reductions-r::), ‘-reduce-r’ (*note -reduce-r::)

          (-reductions-from (lambda (a i) (format "(%s FN %d)" a i)) "INIT" '(1 2 3 4))
              ⇒ '("INIT" "(INIT FN 1)" "((INIT FN 1) FN 2)" "(((INIT FN 1) FN 2) FN 3)" "((((INIT FN 1) FN 2) FN 3) FN 4)")
          (-reductions-from 'max 0 '(2 1 4 3))
              ⇒ '(0 2 2 4 4)
          (-reductions-from '* 1 '(1 2 3 4))
              ⇒ '(1 1 2 6 24)

 -- Function: -reductions-r-from (fn init list)
     Return a list of the intermediate values of the reduction.

     See ‘-reduce-r-from’ (*note -reduce-r-from::) for explanation of
     the arguments.

     See also: ‘-reductions-r’ (*note -reductions-r::), ‘-reductions’
     (*note -reductions::), ‘-reduce’ (*note -reduce::)

          (-reductions-r-from (lambda (i a) (format "(%d FN %s)" i a)) "INIT" '(1 2 3 4))
              ⇒ '("(1 FN (2 FN (3 FN (4 FN INIT))))" "(2 FN (3 FN (4 FN INIT)))" "(3 FN (4 FN INIT))" "(4 FN INIT)" "INIT")
          (-reductions-r-from 'max 0 '(2 1 4 3))
              ⇒ '(4 4 4 3 0)
          (-reductions-r-from '* 1 '(1 2 3 4))
              ⇒ '(24 24 12 4 1)

 -- Function: -reductions (fn list)
     Return a list of the intermediate values of the reduction.

     See ‘-reduce’ (*note -reduce::) for explanation of the arguments.

     See also: ‘-reductions-from’ (*note -reductions-from::),
     ‘-reductions-r’ (*note -reductions-r::), ‘-reduce-r’ (*note
     -reduce-r::)

          (-reductions (lambda (a i) (format "(%s FN %d)" a i)) '(1 2 3 4))
              ⇒ '(1 "(1 FN 2)" "((1 FN 2) FN 3)" "(((1 FN 2) FN 3) FN 4)")
          (-reductions '+ '(1 2 3 4))
              ⇒ '(1 3 6 10)
          (-reductions '* '(1 2 3 4))
              ⇒ '(1 2 6 24)

 -- Function: -reductions-r (fn list)
     Return a list of the intermediate values of the reduction.

     See ‘-reduce-r’ (*note -reduce-r::) for explanation of the
     arguments.

     See also: ‘-reductions-r-from’ (*note -reductions-r-from::),
     ‘-reductions’ (*note -reductions::), ‘-reduce’ (*note -reduce::)

          (-reductions-r (lambda (i a) (format "(%d FN %s)" i a)) '(1 2 3 4))
              ⇒ '("(1 FN (2 FN (3 FN 4)))" "(2 FN (3 FN 4))" "(3 FN 4)" 4)
          (-reductions-r '+ '(1 2 3 4))
              ⇒ '(10 9 7 4)
          (-reductions-r '* '(1 2 3 4))
              ⇒ '(24 24 12 4)

 -- Function: -count (pred list)
     Counts the number of items in LIST where (PRED item) is non-nil.

          (-count 'even? '(1 2 3 4 5))
              ⇒ 2
          (--count (< it 4) '(1 2 3 4))
              ⇒ 3

 -- Function: -sum (list)
     Return the sum of LIST.

          (-sum '())
              ⇒ 0
          (-sum '(1))
              ⇒ 1
          (-sum '(1 2 3 4))
              ⇒ 10

 -- Function: -running-sum (list)
     Return a list with running sums of items in LIST.

     LIST must be non-empty.

          (-running-sum '(1 2 3 4))
              ⇒ '(1 3 6 10)
          (-running-sum '(1))
              ⇒ '(1)
          (-running-sum '())
              ⇒ error

 -- Function: -product (list)
     Return the product of LIST.

          (-product '())
              ⇒ 1
          (-product '(1))
              ⇒ 1
          (-product '(1 2 3 4))
              ⇒ 24

 -- Function: -running-product (list)
     Return a list with running products of items in LIST.

     LIST must be non-empty.

          (-running-product '(1 2 3 4))
              ⇒ '(1 2 6 24)
          (-running-product '(1))
              ⇒ '(1)
          (-running-product '())
              ⇒ error

 -- Function: -inits (list)
     Return all prefixes of LIST.

          (-inits '(1 2 3 4))
              ⇒ '(nil (1) (1 2) (1 2 3) (1 2 3 4))
          (-inits nil)
              ⇒ '(nil)
          (-inits '(1))
              ⇒ '(nil (1))

 -- Function: -tails (list)
     Return all suffixes of LIST

          (-tails '(1 2 3 4))
              ⇒ '((1 2 3 4) (2 3 4) (3 4) (4) nil)
          (-tails nil)
              ⇒ '(nil)
          (-tails '(1))
              ⇒ '((1) nil)

 -- Function: -common-prefix (&rest lists)
     Return the longest common prefix of LISTS.

          (-common-prefix '(1))
              ⇒ '(1)
          (-common-prefix '(1 2) '(3 4) '(1 2))
              ⇒ nil
          (-common-prefix '(1 2) '(1 2 3) '(1 2 3 4))
              ⇒ '(1 2)

 -- Function: -common-suffix (&rest lists)
     Return the longest common suffix of LISTS.

          (-common-suffix '(1))
              ⇒ '(1)
          (-common-suffix '(1 2) '(3 4) '(1 2))
              ⇒ nil
          (-common-suffix '(1 2 3 4) '(2 3 4) '(3 4))
              ⇒ '(3 4)

 -- Function: -min (list)
     Return the smallest value from LIST of numbers or markers.

          (-min '(0))
              ⇒ 0
          (-min '(3 2 1))
              ⇒ 1
          (-min '(1 2 3))
              ⇒ 1

 -- Function: -min-by (comparator list)
     Take a comparison function COMPARATOR and a LIST and return the
     least element of the list by the comparison function.

     See also combinator ‘-on’ (*note -on::) which can transform the
     values before comparing them.

          (-min-by '> '(4 3 6 1))
              ⇒ 1
          (--min-by (> (car it) (car other)) '((1 2 3) (2) (3 2)))
              ⇒ '(1 2 3)
          (--min-by (> (length it) (length other)) '((1 2 3) (2) (3 2)))
              ⇒ '(2)

 -- Function: -max (list)
     Return the largest value from LIST of numbers or markers.

          (-max '(0))
              ⇒ 0
          (-max '(3 2 1))
              ⇒ 3
          (-max '(1 2 3))
              ⇒ 3

 -- Function: -max-by (comparator list)
     Take a comparison function COMPARATOR and a LIST and return the
     greatest element of the list by the comparison function.

     See also combinator ‘-on’ (*note -on::) which can transform the
     values before comparing them.

          (-max-by '> '(4 3 6 1))
              ⇒ 6
          (--max-by (> (car it) (car other)) '((1 2 3) (2) (3 2)))
              ⇒ '(3 2)
          (--max-by (> (length it) (length other)) '((1 2 3) (2) (3 2)))
              ⇒ '(1 2 3)


File: dash.info,  Node: Unfolding,  Next: Predicates,  Prev: Reductions,  Up: Functions

2.5 Unfolding
=============

Operations dual to reductions, building lists from seed value rather
than consuming a list to produce a single value.

 -- Function: -iterate (fun init n)
     Return a list of iterated applications of FUN to INIT.

     This means a list of form:

     (init (fun init) (fun (fun init)) ...)

     N is the length of the returned list.

          (-iterate '1+ 1 10)
              ⇒ '(1 2 3 4 5 6 7 8 9 10)
          (-iterate (lambda (x) (+ x x)) 2 5)
              ⇒ '(2 4 8 16 32)
          (--iterate (* it it) 2 5)
              ⇒ '(2 4 16 256 65536)

 -- Function: -unfold (fun seed)
     Build a list from SEED using FUN.

     This is "dual" operation to ‘-reduce-r’ (*note -reduce-r::): while
     -reduce-r consumes a list to produce a single value, ‘-unfold’
     (*note -unfold::) takes a seed value and builds a (potentially
     infinite!)  list.

     FUN should return ‘nil’ to stop the generating process, or a cons
     (A .  B), where A will be prepended to the result and B is the new
     seed.

          (-unfold (lambda (x) (unless (= x 0) (cons x (1- x)))) 10)
              ⇒ '(10 9 8 7 6 5 4 3 2 1)
          (--unfold (when it (cons it (cdr it))) '(1 2 3 4))
              ⇒ '((1 2 3 4) (2 3 4) (3 4) (4))
          (--unfold (when it (cons it (butlast it))) '(1 2 3 4))
              ⇒ '((1 2 3 4) (1 2 3) (1 2) (1))


File: dash.info,  Node: Predicates,  Next: Partitioning,  Prev: Unfolding,  Up: Functions

2.6 Predicates
==============

 -- Function: -any? (pred list)
     Return t if (PRED x) is non-nil for any x in LIST, else nil.

     Alias: ‘-any-p’, ‘-some?’, ‘-some-p’

          (-any? 'even? '(1 2 3))
              ⇒ t
          (-any? 'even? '(1 3 5))
              ⇒ nil
          (-any? 'null '(1 3 5))
              ⇒ nil

 -- Function: -all? (pred list)
     Return t if (PRED x) is non-nil for all x in LIST, else nil.

     Alias: ‘-all-p’, ‘-every?’, ‘-every-p’

          (-all? 'even? '(1 2 3))
              ⇒ nil
          (-all? 'even? '(2 4 6))
              ⇒ t
          (--all? (= 0 (% it 2)) '(2 4 6))
              ⇒ t

 -- Function: -none? (pred list)
     Return t if (PRED x) is nil for all x in LIST, else nil.

     Alias: ‘-none-p’

          (-none? 'even? '(1 2 3))
              ⇒ nil
          (-none? 'even? '(1 3 5))
              ⇒ t
          (--none? (= 0 (% it 2)) '(1 2 3))
              ⇒ nil

 -- Function: -only-some? (pred list)
     Return ‘t‘ if at least one item of LIST matches PRED and at least
     one item of LIST does not match PRED.  Return ‘nil‘ both if all
     items match the predicate or if none of the items match the
     predicate.

     Alias: ‘-only-some-p’

          (-only-some? 'even? '(1 2 3))
              ⇒ t
          (-only-some? 'even? '(1 3 5))
              ⇒ nil
          (-only-some? 'even? '(2 4 6))
              ⇒ nil

 -- Function: -contains? (list element)
     Return non-nil if LIST contains ELEMENT.

     The test for equality is done with ‘equal’, or with ‘-compare-fn’
     if that’s non-nil.

     Alias: ‘-contains-p’

          (-contains? '(1 2 3) 1)
              ⇒ t
          (-contains? '(1 2 3) 2)
              ⇒ t
          (-contains? '(1 2 3) 4)
              ⇒ nil

 -- Function: -same-items? (list list2)
     Return true if LIST and LIST2 has the same items.

     The order of the elements in the lists does not matter.

     Alias: ‘-same-items-p’

          (-same-items? '(1 2 3) '(1 2 3))
              ⇒ t
          (-same-items? '(1 2 3) '(3 2 1))
              ⇒ t
          (-same-items? '(1 2 3) '(1 2 3 4))
              ⇒ nil

 -- Function: -is-prefix? (prefix list)
     Return non-nil if PREFIX is prefix of LIST.

     Alias: ‘-is-prefix-p’

          (-is-prefix? '(1 2 3) '(1 2 3 4 5))
              ⇒ t
          (-is-prefix? '(1 2 3 4 5) '(1 2 3))
              ⇒ nil
          (-is-prefix? '(1 3) '(1 2 3 4 5))
              ⇒ nil

 -- Function: -is-suffix? (suffix list)
     Return non-nil if SUFFIX is suffix of LIST.

     Alias: ‘-is-suffix-p’

          (-is-suffix? '(3 4 5) '(1 2 3 4 5))
              ⇒ t
          (-is-suffix? '(1 2 3 4 5) '(3 4 5))
              ⇒ nil
          (-is-suffix? '(3 5) '(1 2 3 4 5))
              ⇒ nil

 -- Function: -is-infix? (infix list)
     Return non-nil if INFIX is infix of LIST.

     This operation runs in O(n^2) time

     Alias: ‘-is-infix-p’

          (-is-infix? '(1 2 3) '(1 2 3 4 5))
              ⇒ t
          (-is-infix? '(2 3 4) '(1 2 3 4 5))
              ⇒ t
          (-is-infix? '(3 4 5) '(1 2 3 4 5))
              ⇒ t


File: dash.info,  Node: Partitioning,  Next: Indexing,  Prev: Predicates,  Up: Functions

2.7 Partitioning
================

Functions partitioning the input list into a list of lists.

 -- Function: -split-at (n list)
     Return a list of ((-take N LIST) (-drop N LIST)), in no more than
     one pass through the list.

          (-split-at 3 '(1 2 3 4 5))
              ⇒ '((1 2 3) (4 5))
          (-split-at 17 '(1 2 3 4 5))
              ⇒ '((1 2 3 4 5) nil)

 -- Function: -split-with (pred list)
     Return a list of ((-take-while PRED LIST) (-drop-while PRED LIST)),
     in no more than one pass through the list.

          (-split-with 'even? '(1 2 3 4))
              ⇒ '(nil (1 2 3 4))
          (-split-with 'even? '(2 4 5 6))
              ⇒ '((2 4) (5 6))
          (--split-with (< it 4) '(1 2 3 4 3 2 1))
              ⇒ '((1 2 3) (4 3 2 1))

 -- Macro: -split-on (item list)
     Split the LIST each time ITEM is found.

     Unlike ‘-partition-by’ (*note -partition-by::), the ITEM is
     discarded from the results.  Empty lists are also removed from the
     result.

     Comparison is done by ‘equal’.

     See also ‘-split-when’ (*note -split-when::)

          (-split-on '| '(Nil | Leaf a | Node [Tree a]))
              ⇒ '((Nil) (Leaf a) (Node [Tree a]))
          (-split-on ':endgroup '("a" "b" :endgroup "c" :endgroup "d" "e"))
              ⇒ '(("a" "b") ("c") ("d" "e"))
          (-split-on ':endgroup '("a" "b" :endgroup :endgroup "d" "e"))
              ⇒ '(("a" "b") ("d" "e"))

 -- Function: -split-when (fn list)
     Split the LIST on each element where FN returns non-nil.

     Unlike ‘-partition-by’ (*note -partition-by::), the "matched"
     element is discarded from the results.  Empty lists are also
     removed from the result.

     This function can be thought of as a generalization of
     ‘split-string’.

          (-split-when 'even? '(1 2 3 4 5 6))
              ⇒ '((1) (3) (5))
          (-split-when 'even? '(1 2 3 4 6 8 9))
              ⇒ '((1) (3) (9))
          (--split-when (memq it '(&optional &rest)) '(a b &optional c d &rest args))
              ⇒ '((a b) (c d) (args))

 -- Function: -separate (pred list)
     Return a list of ((-filter PRED LIST) (-remove PRED LIST)), in one
     pass through the list.

          (-separate (lambda (num) (= 0 (% num 2))) '(1 2 3 4 5 6 7))
              ⇒ '((2 4 6) (1 3 5 7))
          (--separate (< it 5) '(3 7 5 9 3 2 1 4 6))
              ⇒ '((3 3 2 1 4) (7 5 9 6))
          (-separate 'cdr '((1 2) (1) (1 2 3) (4)))
              ⇒ '(((1 2) (1 2 3)) ((1) (4)))

 -- Function: -partition (n list)
     Return a new list with the items in LIST grouped into N-sized
     sublists.  If there are not enough items to make the last group
     N-sized, those items are discarded.

          (-partition 2 '(1 2 3 4 5 6))
              ⇒ '((1 2) (3 4) (5 6))
          (-partition 2 '(1 2 3 4 5 6 7))
              ⇒ '((1 2) (3 4) (5 6))
          (-partition 3 '(1 2 3 4 5 6 7))
              ⇒ '((1 2 3) (4 5 6))

 -- Function: -partition-all (n list)
     Return a new list with the items in LIST grouped into N-sized
     sublists.  The last group may contain less than N items.

          (-partition-all 2 '(1 2 3 4 5 6))
              ⇒ '((1 2) (3 4) (5 6))
          (-partition-all 2 '(1 2 3 4 5 6 7))
              ⇒ '((1 2) (3 4) (5 6) (7))
          (-partition-all 3 '(1 2 3 4 5 6 7))
              ⇒ '((1 2 3) (4 5 6) (7))

 -- Function: -partition-in-steps (n step list)
     Return a new list with the items in LIST grouped into N-sized
     sublists at offsets STEP apart.  If there are not enough items to
     make the last group N-sized, those items are discarded.

          (-partition-in-steps 2 1 '(1 2 3 4))
              ⇒ '((1 2) (2 3) (3 4))
          (-partition-in-steps 3 2 '(1 2 3 4))
              ⇒ '((1 2 3))
          (-partition-in-steps 3 2 '(1 2 3 4 5))
              ⇒ '((1 2 3) (3 4 5))

 -- Function: -partition-all-in-steps (n step list)
     Return a new list with the items in LIST grouped into N-sized
     sublists at offsets STEP apart.  The last groups may contain less
     than N items.

          (-partition-all-in-steps 2 1 '(1 2 3 4))
              ⇒ '((1 2) (2 3) (3 4) (4))
          (-partition-all-in-steps 3 2 '(1 2 3 4))
              ⇒ '((1 2 3) (3 4))
          (-partition-all-in-steps 3 2 '(1 2 3 4 5))
              ⇒ '((1 2 3) (3 4 5) (5))

 -- Function: -partition-by (fn list)
     Apply FN to each item in LIST, splitting it each time FN returns a
     new value.

          (-partition-by 'even? '())
              ⇒ '()
          (-partition-by 'even? '(1 1 2 2 2 3 4 6 8))
              ⇒ '((1 1) (2 2 2) (3) (4 6 8))
          (--partition-by (< it 3) '(1 2 3 4 3 2 1))
              ⇒ '((1 2) (3 4 3) (2 1))

 -- Function: -partition-by-header (fn list)
     Apply FN to the first item in LIST.  That is the header value.
     Apply FN to each item in LIST, splitting it each time FN returns
     the header value, but only after seeing at least one other value
     (the body).

          (--partition-by-header (= it 1) '(1 2 3 1 2 1 2 3 4))
              ⇒ '((1 2 3) (1 2) (1 2 3 4))
          (--partition-by-header (> it 0) '(1 2 0 1 0 1 2 3 0))
              ⇒ '((1 2 0) (1 0) (1 2 3 0))
          (-partition-by-header 'even? '(2 1 1 1 4 1 3 5 6 6 1))
              ⇒ '((2 1 1 1) (4 1 3 5) (6 6 1))

 -- Function: -partition-after-pred (pred list)
     Partition directly after each time PRED is true on an element of
     LIST.

          (-partition-after-pred (function oddp) '())
              ⇒ '()
          (-partition-after-pred (function oddp) '(1))
              ⇒ '((1))
          (-partition-after-pred (function oddp) '(0 1))
              ⇒ '((0 1))

 -- Function: -partition-before-pred (pred list)
     Partition directly before each time PRED is true on an element of
     LIST.

          (-partition-before-pred (function oddp) '())
              ⇒ '()
          (-partition-before-pred (function oddp) '(1))
              ⇒ '((1))
          (-partition-before-pred (function oddp) '(0 1))
              ⇒ '((0) (1))

 -- Function: -partition-before-item (item list)
     Partition directly before each time ITEM appears in LIST.

          (-partition-before-item 3 '())
              ⇒ '()
          (-partition-before-item 3 '(1))
              ⇒ '((1))
          (-partition-before-item 3 '(3))
              ⇒ '((3))

 -- Function: -partition-after-item (item list)
     Partition directly after each time ITEM appears in LIST.

          (-partition-after-item 3 '())
              ⇒ '()
          (-partition-after-item 3 '(1))
              ⇒ '((1))
          (-partition-after-item 3 '(3))
              ⇒ '((3))

 -- Function: -group-by (fn list)
     Separate LIST into an alist whose keys are FN applied to the
     elements of LIST.  Keys are compared by ‘equal’.

          (-group-by 'even? '())
              ⇒ '()
          (-group-by 'even? '(1 1 2 2 2 3 4 6 8))
              ⇒ '((nil 1 1 3) (t 2 2 2 4 6 8))
          (--group-by (car (split-string it "/")) '("a/b" "c/d" "a/e"))
              ⇒ '(("a" "a/b" "a/e") ("c" "c/d"))


File: dash.info,  Node: Indexing,  Next: Set operations,  Prev: Partitioning,  Up: Functions

2.8 Indexing
============

Return indices of elements based on predicates, sort elements by indices
etc.

 -- Function: -elem-index (elem list)
     Return the index of the first element in the given LIST which is
     equal to the query element ELEM, or nil if there is no such
     element.

          (-elem-index 2 '(6 7 8 2 3 4))
              ⇒ 3
          (-elem-index "bar" '("foo" "bar" "baz"))
              ⇒ 1
          (-elem-index '(1 2) '((3) (5 6) (1 2) nil))
              ⇒ 2

 -- Function: -elem-indices (elem list)
     Return the indices of all elements in LIST equal to the query
     element ELEM, in ascending order.

          (-elem-indices 2 '(6 7 8 2 3 4 2 1))
              ⇒ '(3 6)
          (-elem-indices "bar" '("foo" "bar" "baz"))
              ⇒ '(1)
          (-elem-indices '(1 2) '((3) (1 2) (5 6) (1 2) nil))
              ⇒ '(1 3)

 -- Function: -find-index (pred list)
     Take a predicate PRED and a LIST and return the index of the first
     element in the list satisfying the predicate, or nil if there is no
     such element.

     See also ‘-first’ (*note -first::).

          (-find-index 'even? '(2 4 1 6 3 3 5 8))
              ⇒ 0
          (--find-index (< 5 it) '(2 4 1 6 3 3 5 8))
              ⇒ 3
          (-find-index (-partial 'string-lessp "baz") '("bar" "foo" "baz"))
              ⇒ 1

 -- Function: -find-last-index (pred list)
     Take a predicate PRED and a LIST and return the index of the last
     element in the list satisfying the predicate, or nil if there is no
     such element.

     See also ‘-last’ (*note -last::).

          (-find-last-index 'even? '(2 4 1 6 3 3 5 8))
              ⇒ 7
          (--find-last-index (< 5 it) '(2 7 1 6 3 8 5 2))
              ⇒ 5
          (-find-last-index (-partial 'string-lessp "baz") '("q" "foo" "baz"))
              ⇒ 1

 -- Function: -find-indices (pred list)
     Return the indices of all elements in LIST satisfying the predicate
     PRED, in ascending order.

          (-find-indices 'even? '(2 4 1 6 3 3 5 8))
              ⇒ '(0 1 3 7)
          (--find-indices (< 5 it) '(2 4 1 6 3 3 5 8))
              ⇒ '(3 7)
          (-find-indices (-partial 'string-lessp "baz") '("bar" "foo" "baz"))
              ⇒ '(1)

 -- Function: -grade-up (comparator list)
     Grade elements of LIST using COMPARATOR relation, yielding a
     permutation vector such that applying this permutation to LIST
     sorts it in ascending order.

          (-grade-up '< '(3 1 4 2 1 3 3))
              ⇒ '(1 4 3 0 5 6 2)
          (let ((l '(3 1 4 2 1 3 3))) (-select-by-indices (-grade-up '< l) l))
              ⇒ '(1 1 2 3 3 3 4)

 -- Function: -grade-down (comparator list)
     Grade elements of LIST using COMPARATOR relation, yielding a
     permutation vector such that applying this permutation to LIST
     sorts it in descending order.

          (-grade-down '< '(3 1 4 2 1 3 3))
              ⇒ '(2 0 5 6 3 1 4)
          (let ((l '(3 1 4 2 1 3 3))) (-select-by-indices (-grade-down '< l) l))
              ⇒ '(4 3 3 3 2 1 1)


File: dash.info,  Node: Set operations,  Next: Other list operations,  Prev: Indexing,  Up: Functions

2.9 Set operations
==================

Operations pretending lists are sets.

 -- Function: -union (list list2)
     Return a new list containing the elements of LIST and elements of
     LIST2 that are not in LIST.  The test for equality is done with
     ‘equal’, or with ‘-compare-fn’ if that’s non-nil.

          (-union '(1 2 3) '(3 4 5))
              ⇒ '(1 2 3 4 5)
          (-union '(1 2 3 4) '())
              ⇒ '(1 2 3 4)
          (-union '(1 1 2 2) '(3 2 1))
              ⇒ '(1 1 2 2 3)

 -- Function: -difference (list list2)
     Return a new list with only the members of LIST that are not in
     LIST2.  The test for equality is done with ‘equal’, or with
     ‘-compare-fn’ if that’s non-nil.

          (-difference '() '())
              ⇒ '()
          (-difference '(1 2 3) '(4 5 6))
              ⇒ '(1 2 3)
          (-difference '(1 2 3 4) '(3 4 5 6))
              ⇒ '(1 2)

 -- Function: -intersection (list list2)
     Return a new list containing only the elements that are members of
     both LIST and LIST2.  The test for equality is done with ‘equal’,
     or with ‘-compare-fn’ if that’s non-nil.

          (-intersection '() '())
              ⇒ '()
          (-intersection '(1 2 3) '(4 5 6))
              ⇒ '()
          (-intersection '(1 2 3 4) '(3 4 5 6))
              ⇒ '(3 4)

 -- Function: -powerset (list)
     Return the power set of LIST.

          (-powerset '())
              ⇒ '(nil)
          (-powerset '(x y z))
              ⇒ '((x y z) (x y) (x z) (x) (y z) (y) (z) nil)

 -- Function: -permutations (list)
     Return the permutations of LIST.

          (-permutations '())
              ⇒ '(nil)
          (-permutations '(1 2))
              ⇒ '((1 2) (2 1))
          (-permutations '(a b c))
              ⇒ '((a b c) (a c b) (b a c) (b c a) (c a b) (c b a))

 -- Function: -distinct (list)
     Return a new list with all duplicates removed.  The test for
     equality is done with ‘equal’, or with ‘-compare-fn’ if that’s
     non-nil.

     Alias: ‘-uniq’

          (-distinct '())
              ⇒ '()
          (-distinct '(1 2 2 4))
              ⇒ '(1 2 4)


File: dash.info,  Node: Other list operations,  Next: Tree operations,  Prev: Set operations,  Up: Functions

2.10 Other list operations
==========================

Other list functions not fit to be classified elsewhere.

 -- Function: -rotate (n list)
     Rotate LIST N places to the right.  With N negative, rotate to the
     left.  The time complexity is O(n).

          (-rotate 3 '(1 2 3 4 5 6 7))
              ⇒ '(5 6 7 1 2 3 4)
          (-rotate -3 '(1 2 3 4 5 6 7))
              ⇒ '(4 5 6 7 1 2 3)
          (-rotate 16 '(1 2 3 4 5 6 7))
              ⇒ '(6 7 1 2 3 4 5)

 -- Function: -repeat (n x)
     Return a list with X repeated N times.  Return nil if N is less
     than 1.

          (-repeat 3 :a)
              ⇒ '(:a :a :a)
          (-repeat 1 :a)
              ⇒ '(:a)
          (-repeat 0 :a)
              ⇒ nil

 -- Function: -cons* (&rest args)
     Make a new list from the elements of ARGS.

     The last 2 members of ARGS are used as the final cons of the result
     so if the final member of ARGS is not a list the result is a dotted
     list.

          (-cons* 1 2)
              ⇒ '(1 . 2)
          (-cons* 1 2 3)
              ⇒ '(1 2 . 3)
          (-cons* 1)
              ⇒ 1

 -- Function: -snoc (list elem &rest elements)
     Append ELEM to the end of the list.

     This is like ‘cons’, but operates on the end of list.

     If ELEMENTS is non nil, append these to the list as well.

          (-snoc '(1 2 3) 4)
              ⇒ '(1 2 3 4)
          (-snoc '(1 2 3) 4 5 6)
              ⇒ '(1 2 3 4 5 6)
          (-snoc '(1 2 3) '(4 5 6))
              ⇒ '(1 2 3 (4 5 6))

 -- Function: -interpose (sep list)
     Return a new list of all elements in LIST separated by SEP.

          (-interpose "-" '())
              ⇒ '()
          (-interpose "-" '("a"))
              ⇒ '("a")
          (-interpose "-" '("a" "b" "c"))
              ⇒ '("a" "-" "b" "-" "c")

 -- Function: -interleave (&rest lists)
     Return a new list of the first item in each list, then the second
     etc.

          (-interleave '(1 2) '("a" "b"))
              ⇒ '(1 "a" 2 "b")
          (-interleave '(1 2) '("a" "b") '("A" "B"))
              ⇒ '(1 "a" "A" 2 "b" "B")
          (-interleave '(1 2 3) '("a" "b"))
              ⇒ '(1 "a" 2 "b")

 -- Function: -zip-with (fn list1 list2)
     Zip the two lists LIST1 and LIST2 using a function FN.  This
     function is applied pairwise taking as first argument element of
     LIST1 and as second argument element of LIST2 at corresponding
     position.

     The anaphoric form ‘--zip-with’ binds the elements from LIST1 as
     symbol ‘it’, and the elements from LIST2 as symbol ‘other’.

          (-zip-with '+ '(1 2 3) '(4 5 6))
              ⇒ '(5 7 9)
          (-zip-with 'cons '(1 2 3) '(4 5 6))
              ⇒ '((1 . 4) (2 . 5) (3 . 6))
          (--zip-with (concat it " and " other) '("Batman" "Jekyll") '("Robin" "Hyde"))
              ⇒ '("Batman and Robin" "Jekyll and Hyde")

 -- Function: -zip (&rest lists)
     Zip LISTS together.  Group the head of each list, followed by the
     second elements of each list, and so on.  The lengths of the
     returned groupings are equal to the length of the shortest input
     list.

     If two lists are provided as arguments, return the groupings as a
     list of cons cells.  Otherwise, return the groupings as a list of
     lists.

     Please note!  This distinction is being removed in an upcoming 3.0
     release of Dash.  If you rely on this behavior, use -zip-pair
     instead.

          (-zip '(1 2 3) '(4 5 6))
              ⇒ '((1 . 4) (2 . 5) (3 . 6))
          (-zip '(1 2 3) '(4 5 6 7))
              ⇒ '((1 . 4) (2 . 5) (3 . 6))
          (-zip '(1 2 3 4) '(4 5 6))
              ⇒ '((1 . 4) (2 . 5) (3 . 6))

 -- Function: -zip-fill (fill-value &rest lists)
     Zip LISTS, with FILL-VALUE padded onto the shorter lists.  The
     lengths of the returned groupings are equal to the length of the
     longest input list.

          (-zip-fill 0 '(1 2 3 4 5) '(6 7 8 9))
              ⇒ '((1 . 6) (2 . 7) (3 . 8) (4 . 9) (5 . 0))

 -- Function: -unzip (lists)
     Unzip LISTS.

     This works just like ‘-zip’ (*note -zip::) but takes a list of
     lists instead of a variable number of arguments, such that

     (-unzip (-zip L1 L2 L3 ...))

     is identity (given that the lists are the same length).

     See also: ‘-zip’ (*note -zip::)

          (-unzip (-zip '(1 2 3) '(a b c) '("e" "f" "g")))
              ⇒ '((1 2 3) (a b c) ("e" "f" "g"))
          (-unzip '((1 2) (3 4) (5 6) (7 8) (9 10)))
              ⇒ '((1 3 5 7 9) (2 4 6 8 10))

 -- Function: -cycle (list)
     Return an infinite copy of LIST that will cycle through the
     elements and repeat from the beginning.

          (-take 5 (-cycle '(1 2 3)))
              ⇒ '(1 2 3 1 2)
          (-take 7 (-cycle '(1 "and" 3)))
              ⇒ '(1 "and" 3 1 "and" 3 1)
          (-zip (-cycle '(1 2 3)) '(1 2))
              ⇒ '((1 . 1) (2 . 2))

 -- Function: -pad (fill-value &rest lists)
     Appends FILL-VALUE to the end of each list in LISTS such that they
     will all have the same length.

          (-pad 0 '())
              ⇒ '(nil)
          (-pad 0 '(1))
              ⇒ '((1))
          (-pad 0 '(1 2 3) '(4 5))
              ⇒ '((1 2 3) (4 5 0))

 -- Function: -table (fn &rest lists)
     Compute outer product of LISTS using function FN.

     The function FN should have the same arity as the number of
     supplied lists.

     The outer product is computed by applying fn to all possible
     combinations created by taking one element from each list in order.
     The dimension of the result is (length lists).

     See also: ‘-table-flat’ (*note -table-flat::)

          (-table '* '(1 2 3) '(1 2 3))
              ⇒ '((1 2 3) (2 4 6) (3 6 9))
          (-table (lambda (a b) (-sum (-zip-with '* a b))) '((1 2) (3 4)) '((1 3) (2 4)))
              ⇒ '((7 15) (10 22))
          (apply '-table 'list (-repeat 3 '(1 2)))
              ⇒ '((((1 1 1) (2 1 1)) ((1 2 1) (2 2 1))) (((1 1 2) (2 1 2)) ((1 2 2) (2 2 2))))

 -- Function: -table-flat (fn &rest lists)
     Compute flat outer product of LISTS using function FN.

     The function FN should have the same arity as the number of
     supplied lists.

     The outer product is computed by applying fn to all possible
     combinations created by taking one element from each list in order.
     The results are flattened, ignoring the tensor structure of the
     result.  This is equivalent to calling:

     (-flatten-n (1- (length lists)) (apply ’-table fn lists))

     but the implementation here is much more efficient.

     See also: ‘-flatten-n’ (*note -flatten-n::), ‘-table’ (*note
     -table::)

          (-table-flat 'list '(1 2 3) '(a b c))
              ⇒ '((1 a) (2 a) (3 a) (1 b) (2 b) (3 b) (1 c) (2 c) (3 c))
          (-table-flat '* '(1 2 3) '(1 2 3))
              ⇒ '(1 2 3 2 4 6 3 6 9)
          (apply '-table-flat 'list (-repeat 3 '(1 2)))
              ⇒ '((1 1 1) (2 1 1) (1 2 1) (2 2 1) (1 1 2) (2 1 2) (1 2 2) (2 2 2))

 -- Function: -first (pred list)
     Return the first x in LIST where (PRED x) is non-nil, else nil.

     To get the first item in the list no questions asked, use ‘car’.

     Alias: ‘-find’

          (-first 'even? '(1 2 3))
              ⇒ 2
          (-first 'even? '(1 3 5))
              ⇒ nil
          (-first 'null '(1 3 5))
              ⇒ nil

 -- Function: -some (pred list)
     Return (PRED x) for the first LIST item where (PRED x) is non-nil,
     else nil.

     Alias: ‘-any’

          (-some 'even? '(1 2 3))
              ⇒ t
          (-some 'null '(1 2 3))
              ⇒ nil
          (-some 'null '(1 2 nil))
              ⇒ t

 -- Function: -last (pred list)
     Return the last x in LIST where (PRED x) is non-nil, else nil.

          (-last 'even? '(1 2 3 4 5 6 3 3 3))
              ⇒ 6
          (-last 'even? '(1 3 7 5 9))
              ⇒ nil
          (--last (> (length it) 3) '("a" "looong" "word" "and" "short" "one"))
              ⇒ "short"

 -- Function: -first-item (list)
     Return the first item of LIST, or nil on an empty list.

     See also: ‘-second-item’ (*note -second-item::), ‘-last-item’
     (*note -last-item::).

     (fn LIST)

          (-first-item '(1 2 3))
              ⇒ 1
          (-first-item nil)
              ⇒ nil
          (let ((list (list 1 2 3))) (setf (-first-item list) 5) list)
              ⇒ '(5 2 3)

 -- Function: -second-item (arg1)
     Return the second item of LIST, or nil if LIST is too short.

     See also: ‘-third-item’ (*note -third-item::).

     (fn LIST)

          (-second-item '(1 2 3))
              ⇒ 2
          (-second-item nil)
              ⇒ nil

 -- Function: -third-item (arg1)
     Return the third item of LIST, or nil if LIST is too short.

     See also: ‘-fourth-item’ (*note -fourth-item::).

     (fn LIST)

          (-third-item '(1 2 3))
              ⇒ 3
          (-third-item nil)
              ⇒ nil

 -- Function: -fourth-item (list)
     Return the fourth item of LIST, or nil if LIST is too short.

     See also: ‘-fifth-item’ (*note -fifth-item::).

          (-fourth-item '(1 2 3 4))
              ⇒ 4
          (-fourth-item nil)
              ⇒ nil

 -- Function: -fifth-item (list)
     Return the fifth item of LIST, or nil if LIST is too short.

     See also: ‘-last-item’ (*note -last-item::).

          (-fifth-item '(1 2 3 4 5))
              ⇒ 5
          (-fifth-item nil)
              ⇒ nil

 -- Function: -last-item (list)
     Return the last item of LIST, or nil on an empty list.

          (-last-item '(1 2 3))
              ⇒ 3
          (-last-item nil)
              ⇒ nil
          (let ((list (list 1 2 3))) (setf (-last-item list) 5) list)
              ⇒ '(1 2 5)

 -- Function: -butlast (list)
     Return a list of all items in list except for the last.

          (-butlast '(1 2 3))
              ⇒ '(1 2)
          (-butlast '(1 2))
              ⇒ '(1)
          (-butlast '(1))
              ⇒ nil

 -- Function: -sort (comparator list)
     Sort LIST, stably, comparing elements using COMPARATOR.  Return the
     sorted list.  LIST is NOT modified by side effects.  COMPARATOR is
     called with two elements of LIST, and should return non-nil if the
     first element should sort before the second.

          (-sort '< '(3 1 2))
              ⇒ '(1 2 3)
          (-sort '> '(3 1 2))
              ⇒ '(3 2 1)
          (--sort (< it other) '(3 1 2))
              ⇒ '(1 2 3)

 -- Function: -list (&rest args)
     Return a list with ARGS.

     If first item of ARGS is already a list, simply return ARGS.  If
     not, return a list with ARGS as elements.

          (-list 1)
              ⇒ '(1)
          (-list 1 2 3)
              ⇒ '(1 2 3)
          (-list '(1 2 3))
              ⇒ '(1 2 3)

 -- Function: -fix (fn list)
     Compute the (least) fixpoint of FN with initial input LIST.

     FN is called at least once, results are compared with ‘equal’.

          (-fix (lambda (l) (-non-nil (--mapcat (-split-at (/ (length it) 2) it) l))) '((1 2 3 4 5 6)))
              ⇒ '((1) (2) (3) (4) (5) (6))
          (let ((data '(("starwars" "scifi") ("jedi" "starwars" "warrior")))) (--fix (-uniq (--mapcat (cons it (cdr (assoc it data))) it)) '("jedi" "book")))
              ⇒ '("jedi" "starwars" "warrior" "scifi" "book")


File: dash.info,  Node: Tree operations,  Next: Threading macros,  Prev: Other list operations,  Up: Functions

2.11 Tree operations
====================

Functions pretending lists are trees.

 -- Function: -tree-seq (branch children tree)
     Return a sequence of the nodes in TREE, in depth-first search
     order.

     BRANCH is a predicate of one argument that returns non-nil if the
     passed argument is a branch, that is, a node that can have
     children.

     CHILDREN is a function of one argument that returns the children of
     the passed branch node.

     Non-branch nodes are simply copied.

          (-tree-seq 'listp 'identity '(1 (2 3) 4 (5 (6 7))))
              ⇒ '((1 (2 3) 4 (5 (6 7))) 1 (2 3) 2 3 4 (5 (6 7)) 5 (6 7) 6 7)
          (-tree-seq 'listp 'reverse '(1 (2 3) 4 (5 (6 7))))
              ⇒ '((1 (2 3) 4 (5 (6 7))) (5 (6 7)) (6 7) 7 6 5 4 (2 3) 3 2 1)
          (--tree-seq (vectorp it) (append it nil) [1 [2 3] 4 [5 [6 7]]])
              ⇒ '([1 [2 3] 4 [5 [6 7]]] 1 [2 3] 2 3 4 [5 [6 7]] 5 [6 7] 6 7)

 -- Function: -tree-map (fn tree)
     Apply FN to each element of TREE while preserving the tree
     structure.

          (-tree-map '1+ '(1 (2 3) (4 (5 6) 7)))
              ⇒ '(2 (3 4) (5 (6 7) 8))
          (-tree-map '(lambda (x) (cons x (expt 2 x))) '(1 (2 3) 4))
              ⇒ '((1 . 2) ((2 . 4) (3 . 8)) (4 . 16))
          (--tree-map (length it) '("<body>" ("<p>" "text" "</p>") "</body>"))
              ⇒ '(6 (3 4 4) 7)

 -- Function: -tree-map-nodes (pred fun tree)
     Call FUN on each node of TREE that satisfies PRED.

     If PRED returns nil, continue descending down this node.  If PRED
     returns non-nil, apply FUN to this node and do not descend further.

          (-tree-map-nodes 'vectorp (lambda (x) (-sum (append x nil))) '(1 [2 3] 4 (5 [6 7] 8)))
              ⇒ '(1 5 4 (5 13 8))
          (-tree-map-nodes 'keywordp (lambda (x) (symbol-name x)) '(1 :foo 4 ((5 6 :bar) :baz 8)))
              ⇒ '(1 ":foo" 4 ((5 6 ":bar") ":baz" 8))
          (--tree-map-nodes (eq (car-safe it) 'add-mode) (-concat it (list :mode 'emacs-lisp-mode)) '(with-mode emacs-lisp-mode (foo bar) (add-mode a b) (baz (add-mode c d))))
              ⇒ '(with-mode emacs-lisp-mode (foo bar) (add-mode a b :mode emacs-lisp-mode) (baz (add-mode c d :mode emacs-lisp-mode)))

 -- Function: -tree-reduce (fn tree)
     Use FN to reduce elements of list TREE.  If elements of TREE are
     lists themselves, apply the reduction recursively.

     FN is first applied to first element of the list and second
     element, then on this result and third element from the list etc.

     See ‘-reduce-r’ (*note -reduce-r::) for how exactly are lists of
     zero or one element handled.

          (-tree-reduce '+ '(1 (2 3) (4 5)))
              ⇒ 15
          (-tree-reduce 'concat '("strings" (" on" " various") ((" levels"))))
              ⇒ "strings on various levels"
          (--tree-reduce (cond ((stringp it) (concat it " " acc)) (t (let ((sn (symbol-name it))) (concat "<" sn ">" acc "</" sn ">")))) '(body (p "some words") (div "more" (b "bold") "words")))
              ⇒ "<body><p>some words</p> <div>more <b>bold</b> words</div></body>"

 -- Function: -tree-reduce-from (fn init-value tree)
     Use FN to reduce elements of list TREE.  If elements of TREE are
     lists themselves, apply the reduction recursively.

     FN is first applied to INIT-VALUE and first element of the list,
     then on this result and second element from the list etc.

     The initial value is ignored on cons pairs as they always contain
     two elements.

          (-tree-reduce-from '+ 1 '(1 (1 1) ((1))))
              ⇒ 8
          (--tree-reduce-from (-concat acc (list it)) nil '(1 (2 3 (4 5)) (6 7)))
              ⇒ '((7 6) ((5 4) 3 2) 1)

 -- Function: -tree-mapreduce (fn folder tree)
     Apply FN to each element of TREE, and make a list of the results.
     If elements of TREE are lists themselves, apply FN recursively to
     elements of these nested lists.

     Then reduce the resulting lists using FOLDER and initial value
     INIT-VALUE.  See ‘-reduce-r-from’ (*note -reduce-r-from::).

     This is the same as calling ‘-tree-reduce’ (*note -tree-reduce::)
     after ‘-tree-map’ (*note -tree-map::) but is twice as fast as it
     only traverse the structure once.

          (-tree-mapreduce 'list 'append '(1 (2 (3 4) (5 6)) (7 (8 9))))
              ⇒ '(1 2 3 4 5 6 7 8 9)
          (--tree-mapreduce 1 (+ it acc) '(1 (2 (4 9) (2 1)) (7 (4 3))))
              ⇒ 9
          (--tree-mapreduce 0 (max acc (1+ it)) '(1 (2 (4 9) (2 1)) (7 (4 3))))
              ⇒ 3

 -- Function: -tree-mapreduce-from (fn folder init-value tree)
     Apply FN to each element of TREE, and make a list of the results.
     If elements of TREE are lists themselves, apply FN recursively to
     elements of these nested lists.

     Then reduce the resulting lists using FOLDER and initial value
     INIT-VALUE.  See ‘-reduce-r-from’ (*note -reduce-r-from::).

     This is the same as calling ‘-tree-reduce-from’ (*note
     -tree-reduce-from::) after ‘-tree-map’ (*note -tree-map::) but is
     twice as fast as it only traverse the structure once.

          (-tree-mapreduce-from 'identity '* 1 '(1 (2 (3 4) (5 6)) (7 (8 9))))
              ⇒ 362880
          (--tree-mapreduce-from (+ it it) (cons it acc) nil '(1 (2 (4 9) (2 1)) (7 (4 3))))
              ⇒ '(2 (4 (8 18) (4 2)) (14 (8 6)))
          (concat "{" (--tree-mapreduce-from (cond ((-cons-pair? it) (concat (symbol-name (car it)) " -> " (symbol-name (cdr it)))) (t (concat (symbol-name it) " : {"))) (concat it (unless (or (equal acc "}") (equal (substring it (1- (length it))) "{")) ", ") acc) "}" '((elips-mode (foo (bar . booze)) (baz . qux)) (c-mode (foo . bla) (bum . bam)))))
              ⇒ "{elips-mode : {foo : {bar -> booze{, baz -> qux{, c-mode : {foo -> bla, bum -> bam}}"

 -- Function: -clone (list)
     Create a deep copy of LIST.  The new list has the same elements and
     structure but all cons are replaced with new ones.  This is useful
     when you need to clone a structure such as plist or alist.

          (let* ((a '(1 2 3)) (b (-clone a))) (nreverse a) b)
              ⇒ '(1 2 3)


File: dash.info,  Node: Threading macros,  Next: Binding,  Prev: Tree operations,  Up: Functions

2.12 Threading macros
=====================

 -- Macro: -> (x &optional form &rest more)
     Thread the expr through the forms.  Insert X as the second item in
     the first form, making a list of it if it is not a list already.
     If there are more forms, insert the first form as the second item
     in second form, etc.

          (-> '(2 3 5))
              ⇒ '(2 3 5)
          (-> '(2 3 5) (append '(8 13)))
              ⇒ '(2 3 5 8 13)
          (-> '(2 3 5) (append '(8 13)) (-slice 1 -1))
              ⇒ '(3 5 8)

 -- Macro: ->> (x &optional form &rest more)
     Thread the expr through the forms.  Insert X as the last item in
     the first form, making a list of it if it is not a list already.
     If there are more forms, insert the first form as the last item in
     second form, etc.

          (->> '(1 2 3) (-map 'square))
              ⇒ '(1 4 9)
          (->> '(1 2 3) (-map 'square) (-remove 'even?))
              ⇒ '(1 9)
          (->> '(1 2 3) (-map 'square) (-reduce '+))
              ⇒ 14

 -- Macro: --> (x &rest forms)
     Starting with the value of X, thread each expression through FORMS.

     Insert X at the position signified by the symbol ‘it’ in the first
     form.  If there are more forms, insert the first form at the
     position signified by ‘it’ in in second form, etc.

          (--> "def" (concat "abc" it "ghi"))
              ⇒ "abcdefghi"
          (--> "def" (concat "abc" it "ghi") (upcase it))
              ⇒ "ABCDEFGHI"
          (--> "def" (concat "abc" it "ghi") upcase)
              ⇒ "ABCDEFGHI"

 -- Macro: -as-> (value variable &rest forms)
     Starting with VALUE, thread VARIABLE through FORMS.

     In the first form, bind VARIABLE to VALUE.  In the second form,
     bind VARIABLE to the result of the first form, and so forth.

          (-as-> 3 my-var (1+ my-var) (list my-var) (mapcar (lambda (ele) (* 2 ele)) my-var))
              ⇒ '(8)
          (-as-> 3 my-var 1+)
              ⇒ 4
          (-as-> 3 my-var)
              ⇒ 3

 -- Macro: -some-> (x &optional form &rest more)
     When expr is non-nil, thread it through the first form (via ‘->’
     (*note ->::)), and when that result is non-nil, through the next
     form, etc.

          (-some-> '(2 3 5))
              ⇒ '(2 3 5)
          (-some-> 5 square)
              ⇒ 25
          (-some-> 5 even? square)
              ⇒ nil

 -- Macro: -some->> (x &optional form &rest more)
     When expr is non-nil, thread it through the first form (via ‘->>’
     (*note ->>::)), and when that result is non-nil, through the next
     form, etc.

          (-some->> '(1 2 3) (-map 'square))
              ⇒ '(1 4 9)
          (-some->> '(1 3 5) (-last 'even?) (+ 100))
              ⇒ nil
          (-some->> '(2 4 6) (-last 'even?) (+ 100))
              ⇒ 106

 -- Macro: -some--> (x &optional form &rest more)
     When expr in non-nil, thread it through the first form (via ‘-->’
     (*note -->::)), and when that result is non-nil, through the next
     form, etc.

          (-some--> "def" (concat "abc" it "ghi"))
              ⇒ "abcdefghi"
          (-some--> nil (concat "abc" it "ghi"))
              ⇒ nil
          (-some--> '(1 3 5) (-filter 'even? it) (append it it) (-map 'square it))
              ⇒ nil


File: dash.info,  Node: Binding,  Next: Side-effects,  Prev: Threading macros,  Up: Functions

2.13 Binding
============

Convenient versions of ‘let‘ and ‘let*‘ constructs combined with flow
control.

 -- Macro: -when-let (var-val &rest body)
     If VAL evaluates to non-nil, bind it to VAR and execute body.

     Note: binding is done according to ‘-let’ (*note -let::).

     (fn (VAR VAL) &rest BODY)

          (-when-let (match-index (string-match "d" "abcd")) (+ match-index 2))
              ⇒ 5
          (-when-let ((&plist :foo foo) (list :foo "foo")) foo)
              ⇒ "foo"
          (-when-let ((&plist :foo foo) (list :bar "bar")) foo)
              ⇒ nil

 -- Macro: -when-let* (vars-vals &rest body)
     If all VALS evaluate to true, bind them to their corresponding VARS
     and execute body.  VARS-VALS should be a list of (VAR VAL) pairs.

     Note: binding is done according to ‘-let*’ (*note -let*::).  VALS
     are evaluated sequentially, and evaluation stops after the first
     nil VAL is encountered.

          (-when-let* ((x 5) (y 3) (z (+ y 4))) (+ x y z))
              ⇒ 15
          (-when-let* ((x 5) (y nil) (z 7)) (+ x y z))
              ⇒ nil

 -- Macro: -if-let (var-val then &rest else)
     If VAL evaluates to non-nil, bind it to VAR and do THEN, otherwise
     do ELSE.

     Note: binding is done according to ‘-let’ (*note -let::).

     (fn (VAR VAL) THEN &rest ELSE)

          (-if-let (match-index (string-match "d" "abc")) (+ match-index 3) 7)
              ⇒ 7
          (--if-let (even? 4) it nil)
              ⇒ t

 -- Macro: -if-let* (vars-vals then &rest else)
     If all VALS evaluate to true, bind them to their corresponding VARS
     and do THEN, otherwise do ELSE.  VARS-VALS should be a list of (VAR
     VAL) pairs.

     Note: binding is done according to ‘-let*’ (*note -let*::).  VALS
     are evaluated sequentially, and evaluation stops after the first
     nil VAL is encountered.

          (-if-let* ((x 5) (y 3) (z 7)) (+ x y z) "foo")
              ⇒ 15
          (-if-let* ((x 5) (y nil) (z 7)) (+ x y z) "foo")
              ⇒ "foo"
          (-if-let* (((_ _ x) '(nil nil 7))) x)
              ⇒ 7

 -- Macro: -let (varlist &rest body)
     Bind variables according to VARLIST then eval BODY.

     VARLIST is a list of lists of the form (PATTERN SOURCE).  Each
     PATTERN is matched against the SOURCE "structurally".  SOURCE is
     only evaluated once for each PATTERN.  Each PATTERN is matched
     recursively, and can therefore contain sub-patterns which are
     matched against corresponding sub-expressions of SOURCE.

     All the SOURCEs are evalled before any symbols are bound (i.e.  "in
     parallel").

     If VARLIST only contains one (PATTERN SOURCE) element, you can
     optionally specify it using a vector and discarding the outer-most
     parens.  Thus

     (-let ((PATTERN SOURCE)) ..)

     becomes

     (-let [PATTERN SOURCE] ..).

     ‘-let’ (*note -let::) uses a convention of not binding places
     (symbols) starting with _ whenever it’s possible.  You can use this
     to skip over entries you don’t care about.  However, this is not
     *always* possible (as a result of implementation) and these symbols
     might get bound to undefined values.

     Following is the overview of supported patterns.  Remember that
     patterns can be matched recursively, so every a, b, aK in the
     following can be a matching construct and not necessarily a
     symbol/variable.

     Symbol:

     a - bind the SOURCE to A.  This is just like regular ‘let’.

     Conses and lists:

     (a) - bind ‘car’ of cons/list to A

     (a .  b) - bind car of cons to A and ‘cdr’ to B

     (a b) - bind car of list to A and ‘cadr’ to B

     (a1 a2 a3 ...)  - bind 0th car of list to A1, 1st to A2, 2nd to A3
     ...

     (a1 a2 a3 ...  aN .  rest) - as above, but bind the Nth cdr to
     REST.

     Vectors:

     [a] - bind 0th element of a non-list sequence to A (works with
     vectors, strings, bit arrays...)

     [a1 a2 a3 ...]  - bind 0th element of non-list sequence to A0, 1st
     to A1, 2nd to A2, ...  If the PATTERN is shorter than SOURCE, the
     values at places not in PATTERN are ignored.  If the PATTERN is
     longer than SOURCE, an ‘error’ is thrown.

     [a1 a2 a3 ...  &rest rest] - as above, but bind the rest of the
     sequence to REST.  This is conceptually the same as improper list
     matching (a1 a2 ...  aN .  rest)

     Key/value stores:

     (&plist key0 a0 ...  keyN aN) - bind value mapped by keyK in the
     SOURCE plist to aK. If the value is not found, aK is nil.  Uses
     ‘plist-get’ to fetch values.

     (&alist key0 a0 ...  keyN aN) - bind value mapped by keyK in the
     SOURCE alist to aK. If the value is not found, aK is nil.  Uses
     ‘assoc’ to fetch values.

     (&hash key0 a0 ...  keyN aN) - bind value mapped by keyK in the
     SOURCE hash table to aK. If the value is not found, aK is nil.
     Uses ‘gethash’ to fetch values.

     Further, special keyword &keys supports "inline" matching of
     plist-like key-value pairs, similarly to &keys keyword of
     ‘cl-defun’.

     (a1 a2 ...  aN &keys key1 b1 ...  keyN bK)

     This binds N values from the list to a1 ...  aN, then interprets
     the cdr as a plist (see key/value matching above).

     A shorthand notation for kv-destructuring exists which allows the
     patterns be optionally left out and derived from the key name in
     the following fashion:

     - a key :foo is converted into ‘foo’ pattern, - a key ’bar is
     converted into ‘bar’ pattern, - a key "baz" is converted into ‘baz’
     pattern.

     That is, the entire value under the key is bound to the derived
     variable without any further destructuring.

     This is possible only when the form following the key is not a
     valid pattern (i.e.  not a symbol, a cons cell or a vector).
     Otherwise the matching proceeds as usual and in case of an invalid
     spec fails with an error.

     Thus the patterns are normalized as follows:

     ;; derive all the missing patterns (&plist :foo ’bar "baz") =>
     (&plist :foo foo ’bar bar "baz" baz)

     ;; we can specify some but not others (&plist :foo ’bar
     explicit-bar) => (&plist :foo foo ’bar explicit-bar)

     ;; nothing happens, we store :foo in x (&plist :foo x) => (&plist
     :foo x)

     ;; nothing happens, we match recursively (&plist :foo (a b c)) =>
     (&plist :foo (a b c))

     You can name the source using the syntax SYMBOL &as PATTERN.  This
     syntax works with lists (proper or improper), vectors and all types
     of maps.

     (list &as a b c) (list 1 2 3)

     binds A to 1, B to 2, C to 3 and LIST to (1 2 3).

     Similarly:

     (bounds &as beg .  end) (cons 1 2)

     binds BEG to 1, END to 2 and BOUNDS to (1 .  2).

     (items &as first .  rest) (list 1 2 3)

     binds FIRST to 1, REST to (2 3) and ITEMS to (1 2 3)

     [vect &as _ b c] [1 2 3]

     binds B to 2, C to 3 and VECT to [1 2 3] (_ avoids binding as
     usual).

     (plist &as &plist :b b) (list :a 1 :b 2 :c 3)

     binds B to 2 and PLIST to (:a 1 :b 2 :c 3).  Same for &alist and
     &hash.

     This is especially useful when we want to capture the result of a
     computation and destructure at the same time.  Consider the form
     (function-returning-complex-structure) returning a list of two
     vectors with two items each.  We want to capture this entire result
     and pass it to another computation, but at the same time we want to
     get the second item from each vector.  We can achieve it with
     pattern

     (result &as [_ a] [_ b]) (function-returning-complex-structure)

     Note: Clojure programmers may know this feature as the ":as
     binding".  The difference is that we put the &as at the front
     because we need to support improper list binding.

          (-let (([a (b c) d] [1 (2 3) 4])) (list a b c d))
              ⇒ '(1 2 3 4)
          (-let [(a b c . d) (list 1 2 3 4 5 6)] (list a b c d))
              ⇒ '(1 2 3 (4 5 6))
          (-let [(&plist :foo foo :bar bar) (list :baz 3 :foo 1 :qux 4 :bar 2)] (list foo bar))
              ⇒ '(1 2)

 -- Macro: -let* (varlist &rest body)
     Bind variables according to VARLIST then eval BODY.

     VARLIST is a list of lists of the form (PATTERN SOURCE).  Each
     PATTERN is matched against the SOURCE structurally.  SOURCE is only
     evaluated once for each PATTERN.

     Each SOURCE can refer to the symbols already bound by this VARLIST.
     This is useful if you want to destructure SOURCE recursively but
     also want to name the intermediate structures.

     See ‘-let’ (*note -let::) for the list of all possible patterns.

          (-let* (((a . b) (cons 1 2)) ((c . d) (cons 3 4))) (list a b c d))
              ⇒ '(1 2 3 4)
          (-let* (((a . b) (cons 1 (cons 2 3))) ((c . d) b)) (list a b c d))
              ⇒ '(1 (2 . 3) 2 3)
          (-let* (((&alist "foo" foo "bar" bar) (list (cons "foo" 1) (cons "bar" (list 'a 'b 'c)))) ((a b c) bar)) (list foo a b c bar))
              ⇒ '(1 a b c (a b c))

 -- Macro: -lambda (match-form &rest body)
     Return a lambda which destructures its input as MATCH-FORM and
     executes BODY.

     Note that you have to enclose the MATCH-FORM in a pair of parens,
     such that:

     (-lambda (x) body) (-lambda (x y ...)  body)

     has the usual semantics of ‘lambda’.  Furthermore, these get
     translated into normal lambda, so there is no performance penalty.

     See ‘-let’ (*note -let::) for the description of destructuring
     mechanism.

          (-map (-lambda ((x y)) (+ x y)) '((1 2) (3 4) (5 6)))
              ⇒ '(3 7 11)
          (-map (-lambda ([x y]) (+ x y)) '([1 2] [3 4] [5 6]))
              ⇒ '(3 7 11)
          (funcall (-lambda ((_ . a) (_ . b)) (-concat a b)) '(1 2 3) '(4 5 6))
              ⇒ '(2 3 5 6)

 -- Macro: -setq (&rest forms)
     Bind each MATCH-FORM to the value of its VAL.

     MATCH-FORM destructuring is done according to the rules of ‘-let’
     (*note -let::).

     This macro allows you to bind multiple variables by destructuring
     the value, so for example:

     (-setq (a b) x (&plist :c c) plist)

     expands roughly speaking to the following code

     (setq a (car x) b (cadr x) c (plist-get plist :c))

     Care is taken to only evaluate each VAL once so that in case of
     multiple assignments it does not cause unexpected side effects.

     (fn [MATCH-FORM VAL]...)

          (progn (-setq a 1) a)
              ⇒ 1
          (progn (-setq (a b) (list 1 2)) (list a b))
              ⇒ '(1 2)
          (progn (-setq (&plist :c c) (list :c "c")) c)
              ⇒ "c"


File: dash.info,  Node: Side-effects,  Next: Destructive operations,  Prev: Binding,  Up: Functions

2.14 Side-effects
=================

Functions iterating over lists for side-effect only.

 -- Function: -each (list fn)
     Call FN with every item in LIST.  Return nil, used for side-effects
     only.

          (let (s) (-each '(1 2 3) (lambda (item) (setq s (cons item s)))))
              ⇒ nil
          (let (s) (-each '(1 2 3) (lambda (item) (setq s (cons item s)))) s)
              ⇒ '(3 2 1)
          (let (s) (--each '(1 2 3) (setq s (cons it s))) s)
              ⇒ '(3 2 1)

 -- Function: -each-while (list pred fn)
     Call FN with every item in LIST while (PRED item) is non-nil.
     Return nil, used for side-effects only.

          (let (s) (-each-while '(2 4 5 6) 'even? (lambda (item) (!cons item s))) s)
              ⇒ '(4 2)
          (let (s) (--each-while '(1 2 3 4) (< it 3) (!cons it s)) s)
              ⇒ '(2 1)

 -- Function: -each-indexed (list fn)
     Call (FN index item) for each item in LIST.

     In the anaphoric form ‘--each-indexed’, the index is exposed as
     symbol ‘it-index’.

     See also: ‘-map-indexed’ (*note -map-indexed::).

          (let (s) (-each-indexed '(a b c) (lambda (index item) (setq s (cons (list item index) s)))) s)
              ⇒ '((c 2) (b 1) (a 0))
          (let (s) (--each-indexed '(a b c) (setq s (cons (list it it-index) s))) s)
              ⇒ '((c 2) (b 1) (a 0))

 -- Function: -each-r (list fn)
     Call FN with every item in LIST in reversed order.  Return nil,
     used for side-effects only.

          (let (s) (-each-r '(1 2 3) (lambda (item) (setq s (cons item s)))))
              ⇒ nil
          (let (s) (-each-r '(1 2 3) (lambda (item) (setq s (cons item s)))) s)
              ⇒ '(1 2 3)
          (let (s) (--each-r '(1 2 3) (setq s (cons it s))) s)
              ⇒ '(1 2 3)

 -- Function: -each-r-while (list pred fn)
     Call FN with every item in reversed LIST while (PRED item) is
     non-nil.  Return nil, used for side-effects only.

          (let (s) (-each-r-while '(2 4 5 6) 'even? (lambda (item) (!cons item s))) s)
              ⇒ '(6)
          (let (s) (--each-r-while '(1 2 3 4) (>= it 3) (!cons it s)) s)
              ⇒ '(3 4)

 -- Function: -dotimes (num fn)
     Repeatedly calls FN (presumably for side-effects) passing in
     integers from 0 through NUM-1.

          (let (s) (-dotimes 3 (lambda (n) (!cons n s))) s)
              ⇒ '(2 1 0)
          (let (s) (--dotimes 5 (!cons it s)) s)
              ⇒ '(4 3 2 1 0)

 -- Macro: -doto (eval-initial-value &rest forms)
     Eval a form, then insert that form as the 2nd argument to other
     forms.  The EVAL-INITIAL-VALUE form is evaluated once.  Its result
     is passed to FORMS, which are then evaluated sequentially.  Returns
     the target form.

          (-doto '(1 2 3) (!cdr) (!cdr))
              ⇒ '(3)
          (-doto '(1 . 2) (setcar 3) (setcdr 4))
              ⇒ '(3 . 4)

 -- Macro: --doto (eval-initial-value &rest forms)
     Anaphoric form of ‘-doto’ (*note -doto::).  Note: ‘it’ is not
     required in each form.

          (gethash "key" (--doto (make-hash-table :test 'equal) (puthash "key" "value" it)))
              ⇒ "value"


File: dash.info,  Node: Destructive operations,  Next: Function combinators,  Prev: Side-effects,  Up: Functions

2.15 Destructive operations
===========================

 -- Macro: !cons (car cdr)
     Destructive: Set CDR to the cons of CAR and CDR.

          (let (l) (!cons 5 l) l)
              ⇒ '(5)
          (let ((l '(3))) (!cons 5 l) l)
              ⇒ '(5 3)

 -- Macro: !cdr (list)
     Destructive: Set LIST to the cdr of LIST.

          (let ((l '(3))) (!cdr l) l)
              ⇒ '()
          (let ((l '(3 5))) (!cdr l) l)
              ⇒ '(5)


File: dash.info,  Node: Function combinators,  Prev: Destructive operations,  Up: Functions

2.16 Function combinators
=========================

These combinators require Emacs 24 for its lexical scope.  So they are
offered in a separate package: ‘dash-functional‘.

 -- Function: -partial (fn &rest args)
     Takes a function FN and fewer than the normal arguments to FN, and
     returns a fn that takes a variable number of additional ARGS.  When
     called, the returned function calls FN with ARGS first and then
     additional args.

          (funcall (-partial '- 5) 3)
              ⇒ 2
          (funcall (-partial '+ 5 2) 3)
              ⇒ 10

 -- Function: -rpartial (fn &rest args)
     Takes a function FN and fewer than the normal arguments to FN, and
     returns a fn that takes a variable number of additional ARGS.  When
     called, the returned function calls FN with the additional args
     first and then ARGS.

          (funcall (-rpartial '- 5) 8)
              ⇒ 3
          (funcall (-rpartial '- 5 2) 10)
              ⇒ 3

 -- Function: -juxt (&rest fns)
     Takes a list of functions and returns a fn that is the
     juxtaposition of those fns.  The returned fn takes a variable
     number of args, and returns a list containing the result of
     applying each fn to the args (left-to-right).

          (funcall (-juxt '+ '-) 3 5)
              ⇒ '(8 -2)
          (-map (-juxt 'identity 'square) '(1 2 3))
              ⇒ '((1 1) (2 4) (3 9))

 -- Function: -compose (&rest fns)
     Takes a list of functions and returns a fn that is the composition
     of those fns.  The returned fn takes a variable number of
     arguments, and returns the result of applying each fn to the result
     of applying the previous fn to the arguments (right-to-left).

          (funcall (-compose 'square '+) 2 3)
              ⇒ (square (+ 2 3))
          (funcall (-compose 'identity 'square) 3)
              ⇒ (square 3)
          (funcall (-compose 'square 'identity) 3)
              ⇒ (square 3)

 -- Function: -applify (fn)
     Changes an n-arity function FN to a 1-arity function that expects a
     list with n items as arguments

          (-map (-applify '+) '((1 1 1) (1 2 3) (5 5 5)))
              ⇒ '(3 6 15)
          (-map (-applify (lambda (a b c) (\` ((\, a) ((\, b) ((\, c))))))) '((1 1 1) (1 2 3) (5 5 5)))
              ⇒ '((1 (1 (1))) (1 (2 (3))) (5 (5 (5))))
          (funcall (-applify '<) '(3 6))
              ⇒ t

 -- Function: -on (operator transformer)
     Return a function of two arguments that first applies TRANSFORMER
     to each of them and then applies OPERATOR on the results (in the
     same order).

     In types: (b -> b -> c) -> (a -> b) -> a -> a -> c

          (-sort (-on '< 'length) '((1 2 3) (1) (1 2)))
              ⇒ '((1) (1 2) (1 2 3))
          (-min-by (-on '> 'length) '((1 2 3) (4) (1 2)))
              ⇒ '(4)
          (-min-by (-on 'string-lessp 'number-to-string) '(2 100 22))
              ⇒ 22

 -- Function: -flip (func)
     Swap the order of arguments for binary function FUNC.

     In types: (a -> b -> c) -> b -> a -> c

          (funcall (-flip '<) 2 1)
              ⇒ t
          (funcall (-flip '-) 3 8)
              ⇒ 5
          (-sort (-flip '<) '(4 3 6 1))
              ⇒ '(6 4 3 1)

 -- Function: -const (c)
     Return a function that returns C ignoring any additional arguments.

     In types: a -> b -> a

          (funcall (-const 2) 1 3 "foo")
              ⇒ 2
          (-map (-const 1) '("a" "b" "c" "d"))
              ⇒ '(1 1 1 1)
          (-sum (-map (-const 1) '("a" "b" "c" "d")))
              ⇒ 4

 -- Macro: -cut (&rest params)
     Take n-ary function and n arguments and specialize some of them.
     Arguments denoted by <> will be left unspecialized.

     See SRFI-26 for detailed description.

          (funcall (-cut list 1 <> 3 <> 5) 2 4)
              ⇒ '(1 2 3 4 5)
          (-map (-cut funcall <> 5) '(1+ 1- (lambda (x) (/ 1.0 x))))
              ⇒ '(6 4 0.2)
          (-map (-cut <> 1 2 3) (list 'list 'vector 'string))
              ⇒ '((1 2 3) [1 2 3] "
")

 -- Function: -not (pred)
     Take a unary predicate PRED and return a unary predicate that
     returns t if PRED returns nil and nil if PRED returns non-nil.

          (funcall (-not 'even?) 5)
              ⇒ t
          (-filter (-not (-partial '< 4)) '(1 2 3 4 5 6 7 8))
              ⇒ '(1 2 3 4)

 -- Function: -orfn (&rest preds)
     Take list of unary predicates PREDS and return a unary predicate
     with argument x that returns non-nil if at least one of the PREDS
     returns non-nil on x.

     In types: [a -> Bool] -> a -> Bool

          (-filter (-orfn 'even? (-partial (-flip '<) 5)) '(1 2 3 4 5 6 7 8 9 10))
              ⇒ '(1 2 3 4 6 8 10)
          (funcall (-orfn 'stringp 'even?) "foo")
              ⇒ t

 -- Function: -andfn (&rest preds)
     Take list of unary predicates PREDS and return a unary predicate
     with argument x that returns non-nil if all of the PREDS returns
     non-nil on x.

     In types: [a -> Bool] -> a -> Bool

          (funcall (-andfn (-cut < <> 10) 'even?) 6)
              ⇒ t
          (funcall (-andfn (-cut < <> 10) 'even?) 12)
              ⇒ nil
          (-filter (-andfn (-not 'even?) (-cut >= 5 <>)) '(1 2 3 4 5 6 7 8 9 10))
              ⇒ '(1 3 5)

 -- Function: -iteratefn (fn n)
     Return a function FN composed N times with itself.

     FN is a unary function.  If you need to use a function of higher
     arity, use ‘-applify’ (*note -applify::) first to turn it into a
     unary function.

     With n = 0, this acts as identity function.

     In types: (a -> a) -> Int -> a -> a.

     This function satisfies the following law:

     (funcall (-iteratefn fn n) init) = (-last-item (-iterate fn init
     (1+ n))).

          (funcall (-iteratefn (lambda (x) (* x x)) 3) 2)
              ⇒ 256
          (funcall (-iteratefn '1+ 3) 1)
              ⇒ 4
          (funcall (-iteratefn 'cdr 3) '(1 2 3 4 5))
              ⇒ '(4 5)

 -- Function: -fixfn (fn &optional equal-test halt-test)
     Return a function that computes the (least) fixpoint of FN.

     FN must be a unary function.  The returned lambda takes a single
     argument, X, the initial value for the fixpoint iteration.  The
     iteration halts when either of the following conditions is
     satisified:

     1.  Iteration converges to the fixpoint, with equality being tested
     using EQUAL-TEST.  If EQUAL-TEST is not specified, ‘equal’ is used.
     For functions over the floating point numbers, it may be necessary
     to provide an appropriate appoximate comparsion test.

     2.  HALT-TEST returns a non-nil value.  HALT-TEST defaults to a
     simple counter that returns t after ‘-fixfn-max-iterations’, to
     guard against infinite iteration.  Otherwise, HALT-TEST must be a
     function that accepts a single argument, the current value of X,
     and returns non-nil as long as iteration should continue.  In this
     way, a more sophisticated convergence test may be supplied by the
     caller.

     The return value of the lambda is either the fixpoint or, if
     iteration halted before converging, a cons with car ‘halted’ and
     cdr the final output from HALT-TEST.

     In types: (a -> a) -> a -> a.

          (funcall (-fixfn 'cos 'approx-equal) 0.7)
              ⇒ 0.7390851332151607
          (funcall (-fixfn (lambda (x) (expt (+ x 10) 0.25))) 2.0)
              ⇒ 1.8555845286409378
          (funcall (-fixfn 'sin 'approx-equal) 0.1)
              ⇒ '(halted . t)

 -- Function: -prodfn (&rest fns)
     Take a list of n functions and return a function that takes a list
     of length n, applying i-th function to i-th element of the input
     list.  Returns a list of length n.

     In types (for n=2): ((a -> b), (c -> d)) -> (a, c) -> (b, d)

     This function satisfies the following laws:

     (-compose (-prodfn f g ...)  (-prodfn f’ g’ ...))  = (-prodfn
     (-compose f f’) (-compose g g’) ...)  (-prodfn f g ...)  = (-juxt
     (-compose f (-partial ’nth 0)) (-compose g (-partial ’nth 1)) ...)
     (-compose (-prodfn f g ...)  (-juxt f’ g’ ...))  = (-juxt (-compose
     f f’) (-compose g g’) ...)  (-compose (-partial ’nth n) (-prod f1
     f2 ...))  = (-compose fn (-partial ’nth n))

          (funcall (-prodfn '1+ '1- 'number-to-string) '(1 2 3))
              ⇒ '(2 1 "3")
          (-map (-prodfn '1+ '1-) '((1 2) (3 4) (5 6) (7 8)))
              ⇒ '((2 1) (4 3) (6 5) (8 7))
          (apply '+ (funcall (-prodfn 'length 'string-to-number) '((1 2 3) "15")))
              ⇒ 18


File: dash.info,  Node: Development,  Next: Index,  Prev: Functions,  Up: Top

3 Development
*************

The dash repository is hosted on GitHub:
<https://github.com/magnars/dash.el>

* Menu:

* Contribute::          How to contribute
* Changes::             List of significant changes by version
* Contributors::        List of contributors


File: dash.info,  Node: Contribute,  Next: Changes,  Up: Development

3.1 Contribute
==============

Yes, please do.  Pure functions in the list manipulation realm only,
please.  There’s a suite of tests in dev/examples.el, so remember to add
tests for your function, or it might get broken later.

   Run the tests with ‘./run-tests.sh’.  Create the docs with
‘./create-docs.sh’.  I highly recommend that you install these as a
pre-commit hook, so that the tests are always running and the docs are
always in sync:

cp pre-commit.sh .git/hooks/pre-commit

   Oh, and don’t edit ‘README.md’ directly, it is auto-generated.
Change ‘readme-template.md’ or ‘examples-to-docs.el’ instead.  The same
goes for the info manual.


File: dash.info,  Node: Changes,  Next: Contributors,  Prev: Contribute,  Up: Development

3.2 Changes
===========

Changes in 2.10:

   • Add ‘-let’ destructuring to ‘-if-let’ and ‘-when-let’ (Fredrik
     Bergroth)

Changes in 2.9:

   • Add ‘-let’, ‘-let*’ and ‘-lambda’ with destructuring
   • Add ‘-tree-seq’ and ‘-tree-map-nodes’
   • Add ‘-non-nil’
   • Add ‘-fix’
   • Add ‘-fixfn’ (dash-functional 1.2)
   • Add ‘-copy’ (Wilfred Hughes)

Changes in 2.8:

   • Add ‘-butlast’

Changes in 2.7:

   • ‘-zip’ now supports more than two lists (Steve Lamb)
   • Add ‘-cycle’, ‘-pad’, ‘-annotate’, ‘-zip-fill’ (Steve Lamb)
   • Add ‘-table’, ‘-table-flat’ (finite cartesian product)
   • Add ‘-flatten-n’
   • ‘-slice’ now supports "step" argument
   • Add functional combinators ‘-iteratefn’, ‘-prodfn’
   • Add ‘-replace’, ‘-splice’, ‘-splice-list’ which generalize
     ‘-replace-at’ and ‘-insert-at’
   • Add ‘-compose’, ‘-iteratefn’ and ‘-prodfn’ (dash-functional 1.1)

Changes in 2.6:

   • Add ‘-is-prefix-p’, ‘-is-suffix-p’, ‘-is-infix-p’ (Matus Goljer)
   • Add ‘-iterate’, ‘-unfold’ (Matus Goljer)
   • Add ‘-split-on’, ‘-split-when’ (Matus Goljer)
   • Add ‘-find-last-index’ (Matus Goljer)
   • Add ‘-list’ (Johan Andersson)

Changes in 2.5:

   • Add ‘-same-items?’ (Johan Andersson)
   • A few bugfixes

Changes in 2.4:

   • Add ‘-snoc’ (Matus Goljer)
   • Add ‘-replace-at’, ‘-update-at’, ‘-remove-at’, and
     ‘-remove-at-indices’ (Matus Goljer)

Changes in 2.3:

   • Add tree operations (Matus Goljer)
   • Make font-lock optional

Changes in 2.2:

   • Add ‘-compose’ (Christina Whyte)

Changes in 2.1:

   • Add indexing operations (Matus Goljer)

Changes in 2.0:

   • Split out ‘dash-functional.el’ (Matus Goljer)
   • Add ‘-andfn’, ‘-orfn’, ‘-not’, ‘-cut’, ‘-const’, ‘-flip’ and ‘-on’.
     (Matus Goljer)
   • Fix ‘-min’, ‘-max’, ‘-min-by’ and ‘-max-by’ (Matus Goljer)

Changes in 1.8:

   • Add ‘-first-item’ and ‘-last-item’ (Wilfred Hughes)

Changes in 1.7:

   • Add ‘-rotate’ (Matus Goljer)

Changes in 1.6:

   • Add ‘-min’, ‘-max’, ‘-min-by’ and ‘-max-by’ (Johan Andersson)

Changes in 1.5:

   • Add ‘-sum’ and ‘-product’ (Johan Andersson)

Changes in 1.4:

   • Add ‘-sort’
   • Add ‘-reduce-r’ (Matus Goljer)
   • Add ‘-reduce-r-from’ (Matus Goljer)

Changes in 1.3:

   • Add ‘-partition-in-steps’
   • Add ‘-partition-all-in-steps’

Changes in 1.2:

   • Add ‘-last’ (Matus Goljer)
   • Add ‘-insert-at’ (Emanuel Evans)
   • Add ‘-when-let’ and ‘-if-let’ (Emanuel Evans)
   • Add ‘-when-let*’ and ‘-if-let*’ (Emanuel Evans)
   • Some bugfixes


File: dash.info,  Node: Contributors,  Prev: Changes,  Up: Development

3.3 Contributors
================

   • Matus Goljer (https://github.com/Fuco1) contributed lots of
     features and functions.
   • Takafumi Arakaki (https://github.com/tkf) contributed ‘-group-by’.
   • tali713 (https://github.com/tali713) is the author of ‘-applify’.
   • Víctor M. Valenzuela (https://github.com/vemv) contributed
     ‘-repeat’.
   • Nic Ferrier (https://github.com/nicferrier) contributed ‘-cons*’.
   • Wilfred Hughes (https://github.com/Wilfred) contributed ‘-slice’,
     ‘-first-item’ and ‘-last-item’.
   • Emanuel Evans (https://github.com/shosti) contributed ‘-if-let’,
     ‘-when-let’ and ‘-insert-at’.
   • Johan Andersson (https://github.com/rejeep) contributed ‘-sum’,
     ‘-product’ and ‘-same-items?’
   • Christina Whyte (https://github.com/kurisuwhyte) contributed
     ‘-compose’
   • Steve Lamb (https://github.com/steventlamb) contributed ‘-cycle’,
     ‘-pad’, ‘-annotate’, ‘-zip-fill’ and an n-ary version of ‘-zip’.
   • Fredrik Bergroth (https://github.com/fbergroth) made the ‘-if-let’
     family use ‘-let’ destructuring and improved script for generating
     documentation.
   • Mark Oteiza (https://github.com/holomorph) contributed the script
     to create an info manual.
   • Vasilij Schneidermann (https://github.com/wasamasa) contributed
     ‘-some’.
   • William West (https://github.com/occidens) made ‘-fixfn’ more
     robust at handling floats.

   Thanks!


File: dash.info,  Node: Index,  Prev: Development,  Up: Top

Index
*****

[index]
* Menu:

* !cdr:                                  Destructive operations.
                                                              (line  14)
* !cons:                                 Destructive operations.
                                                              (line   6)
* -->:                                   Threading macros.    (line  32)
* --doto:                                Side-effects.        (line  81)
* ->:                                    Threading macros.    (line   6)
* ->>:                                   Threading macros.    (line  19)
* -all?:                                 Predicates.          (line  18)
* -andfn:                                Function combinators.
                                                              (line 138)
* -annotate:                             Maps.                (line  79)
* -any?:                                 Predicates.          (line   6)
* -applify:                              Function combinators.
                                                              (line  55)
* -as->:                                 Threading macros.    (line  46)
* -butlast:                              Other list operations.
                                                              (line 313)
* -clone:                                Tree operations.     (line 122)
* -common-prefix:                        Reductions.          (line 223)
* -common-suffix:                        Reductions.          (line 233)
* -compose:                              Function combinators.
                                                              (line  42)
* -concat:                               List to list.        (line  22)
* -cons*:                                Other list operations.
                                                              (line  30)
* -const:                                Function combinators.
                                                              (line  92)
* -contains?:                            Predicates.          (line  57)
* -copy:                                 Maps.                (line 134)
* -count:                                Reductions.          (line 151)
* -cut:                                  Function combinators.
                                                              (line 104)
* -cycle:                                Other list operations.
                                                              (line 141)
* -difference:                           Set operations.      (line  20)
* -distinct:                             Set operations.      (line  62)
* -dotimes:                              Side-effects.        (line  61)
* -doto:                                 Side-effects.        (line  70)
* -drop:                                 Sublist selection.   (line 124)
* -drop-last:                            Sublist selection.   (line 136)
* -drop-while:                           Sublist selection.   (line 157)
* -each:                                 Side-effects.        (line   8)
* -each-indexed:                         Side-effects.        (line  28)
* -each-r:                               Side-effects.        (line  41)
* -each-r-while:                         Side-effects.        (line  52)
* -each-while:                           Side-effects.        (line  19)
* -elem-index:                           Indexing.            (line   9)
* -elem-indices:                         Indexing.            (line  21)
* -fifth-item:                           Other list operations.
                                                              (line 293)
* -filter:                               Sublist selection.   (line   8)
* -find-index:                           Indexing.            (line  32)
* -find-indices:                         Indexing.            (line  60)
* -find-last-index:                      Indexing.            (line  46)
* -first:                                Other list operations.
                                                              (line 207)
* -first-item:                           Other list operations.
                                                              (line 244)
* -fix:                                  Other list operations.
                                                              (line 349)
* -fixfn:                                Function combinators.
                                                              (line 175)
* -flatten:                              List to list.        (line  33)
* -flatten-n:                            List to list.        (line  55)
* -flip:                                 Function combinators.
                                                              (line  80)
* -fourth-item:                          Other list operations.
                                                              (line 283)
* -grade-down:                           Indexing.            (line  81)
* -grade-up:                             Indexing.            (line  71)
* -group-by:                             Partitioning.        (line 187)
* -if-let:                               Binding.             (line  36)
* -if-let*:                              Binding.             (line  49)
* -inits:                                Reductions.          (line 203)
* -insert-at:                            List to list.        (line 109)
* -interleave:                           Other list operations.
                                                              (line  68)
* -interpose:                            Other list operations.
                                                              (line  58)
* -intersection:                         Set operations.      (line  32)
* -is-infix?:                            Predicates.          (line 110)
* -is-prefix?:                           Predicates.          (line  86)
* -is-suffix?:                           Predicates.          (line  98)
* -iterate:                              Unfolding.           (line   9)
* -iteratefn:                            Function combinators.
                                                              (line 152)
* -juxt:                                 Function combinators.
                                                              (line  31)
* -keep:                                 List to list.        (line   8)
* -lambda:                               Binding.             (line 252)
* -last:                                 Other list operations.
                                                              (line 234)
* -last-item:                            Other list operations.
                                                              (line 303)
* -let:                                  Binding.             (line  65)
* -let*:                                 Binding.             (line 232)
* -list:                                 Other list operations.
                                                              (line 336)
* -map:                                  Maps.                (line  10)
* -map-first:                            Maps.                (line  37)
* -map-indexed:                          Maps.                (line  65)
* -map-last:                             Maps.                (line  51)
* -map-when:                             Maps.                (line  21)
* -mapcat:                               Maps.                (line 123)
* -max:                                  Reductions.          (line 267)
* -max-by:                               Reductions.          (line 277)
* -min:                                  Reductions.          (line 243)
* -min-by:                               Reductions.          (line 253)
* -non-nil:                              Sublist selection.   (line  79)
* -none?:                                Predicates.          (line  30)
* -not:                                  Function combinators.
                                                              (line 117)
* -on:                                   Function combinators.
                                                              (line  66)
* -only-some?:                           Predicates.          (line  42)
* -orfn:                                 Function combinators.
                                                              (line 126)
* -pad:                                  Other list operations.
                                                              (line 152)
* -partial:                              Function combinators.
                                                              (line   9)
* -partition:                            Partitioning.        (line  74)
* -partition-after-item:                 Partitioning.        (line 177)
* -partition-after-pred:                 Partitioning.        (line 145)
* -partition-all:                        Partitioning.        (line  86)
* -partition-all-in-steps:               Partitioning.        (line 109)
* -partition-before-item:                Partitioning.        (line 167)
* -partition-before-pred:                Partitioning.        (line 156)
* -partition-by:                         Partitioning.        (line 121)
* -partition-by-header:                  Partitioning.        (line 132)
* -partition-in-steps:                   Partitioning.        (line  97)
* -permutations:                         Set operations.      (line  52)
* -powerset:                             Set operations.      (line  44)
* -prodfn:                               Function combinators.
                                                              (line 209)
* -product:                              Reductions.          (line 181)
* -reduce:                               Reductions.          (line  46)
* -reduce-from:                          Reductions.          (line   8)
* -reduce-r:                             Reductions.          (line  65)
* -reduce-r-from:                        Reductions.          (line  27)
* -reductions:                           Reductions.          (line 119)
* -reductions-from:                      Reductions.          (line  87)
* -reductions-r:                         Reductions.          (line 135)
* -reductions-r-from:                    Reductions.          (line 103)
* -remove:                               Sublist selection.   (line  23)
* -remove-at:                            List to list.        (line 145)
* -remove-at-indices:                    List to list.        (line 158)
* -remove-first:                         Sublist selection.   (line  37)
* -remove-item:                          Sublist selection.   (line  67)
* -remove-last:                          Sublist selection.   (line  52)
* -repeat:                               Other list operations.
                                                              (line  19)
* -replace:                              List to list.        (line  67)
* -replace-at:                           List to list.        (line 120)
* -replace-first:                        List to list.        (line  81)
* -replace-last:                         List to list.        (line  95)
* -rotate:                               Other list operations.
                                                              (line   8)
* -rpartial:                             Function combinators.
                                                              (line  20)
* -running-product:                      Reductions.          (line 191)
* -running-sum:                          Reductions.          (line 169)
* -same-items?:                          Predicates.          (line  72)
* -second-item:                          Other list operations.
                                                              (line 259)
* -select-by-indices:                    Sublist selection.   (line 168)
* -select-column:                        Sublist selection.   (line 198)
* -select-columns:                       Sublist selection.   (line 179)
* -separate:                             Partitioning.        (line  63)
* -setq:                                 Binding.             (line 274)
* -slice:                                Sublist selection.   (line  85)
* -snoc:                                 Other list operations.
                                                              (line  44)
* -some:                                 Other list operations.
                                                              (line 221)
* -some-->:                              Threading macros.    (line  83)
* -some->:                               Threading macros.    (line  59)
* -some->>:                              Threading macros.    (line  71)
* -sort:                                 Other list operations.
                                                              (line 323)
* -splice:                               Maps.                (line  90)
* -splice-list:                          Maps.                (line 110)
* -split-at:                             Partitioning.        (line   8)
* -split-on:                             Partitioning.        (line  28)
* -split-when:                           Partitioning.        (line  46)
* -split-with:                           Partitioning.        (line  17)
* -sum:                                  Reductions.          (line 159)
* -table:                                Other list operations.
                                                              (line 163)
* -table-flat:                           Other list operations.
                                                              (line 182)
* -tails:                                Reductions.          (line 213)
* -take:                                 Sublist selection.   (line 101)
* -take-last:                            Sublist selection.   (line 112)
* -take-while:                           Sublist selection.   (line 146)
* -third-item:                           Other list operations.
                                                              (line 271)
* -tree-map:                             Tree operations.     (line  28)
* -tree-map-nodes:                       Tree operations.     (line  39)
* -tree-mapreduce:                       Tree operations.     (line  84)
* -tree-mapreduce-from:                  Tree operations.     (line 103)
* -tree-reduce:                          Tree operations.     (line  52)
* -tree-reduce-from:                     Tree operations.     (line  69)
* -tree-seq:                             Tree operations.     (line   8)
* -unfold:                               Unfolding.           (line  25)
* -union:                                Set operations.      (line   8)
* -unzip:                                Other list operations.
                                                              (line 124)
* -update-at:                            List to list.        (line 132)
* -when-let:                             Binding.             (line   9)
* -when-let*:                            Binding.             (line  23)
* -zip:                                  Other list operations.
                                                              (line  95)
* -zip-fill:                             Other list operations.
                                                              (line 116)
* -zip-with:                             Other list operations.
                                                              (line  79)



Tag Table:
Node: Top946
Node: Installation2425
Node: Using in a package3001
Node: Syntax highlighting of dash functions3365
Node: Functions3748
Node: Maps4959
Ref: -map5254
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Ref: -map-first6173
Ref: -map-last6651
Ref: -map-indexed7124
Ref: -annotate7604
Ref: -splice8094
Ref: -splice-list8875
Ref: -mapcat9337
Ref: -copy9713
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Ref: -filter10110
Ref: -remove10562
Ref: -remove-first10968
Ref: -remove-last11495
Ref: -remove-item12016
Ref: -non-nil12410
Ref: -slice12569
Ref: -take13101
Ref: -take-last13409
Ref: -drop13732
Ref: -drop-last14005
Ref: -take-while14265
Ref: -drop-while14615
Ref: -select-by-indices14971
Ref: -select-columns15485
Ref: -select-column16191
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Ref: -keep16847
Ref: -concat17350
Ref: -flatten17647
Ref: -flatten-n18406
Ref: -replace18793
Ref: -replace-first19256
Ref: -replace-last19752
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Ref: -replace-at20568
Ref: -update-at20958
Ref: -remove-at21449
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Ref: -reduce-from22688
Ref: -reduce-r-from23454
Ref: -reduce24221
Ref: -reduce-r24950
Ref: -reductions-from25821
Ref: -reductions-r-from26536
Ref: -reductions27261
Ref: -reductions-r27886
Ref: -count28521
Ref: -sum28745
Ref: -running-sum28934
Ref: -product29227
Ref: -running-product29436
Ref: -inits29749
Ref: -tails29997
Ref: -common-prefix30244
Ref: -common-suffix30541
Ref: -min30838
Ref: -min-by31064
Ref: -max31587
Ref: -max-by31812
Node: Unfolding32340
Ref: -iterate32579
Ref: -unfold33024
Node: Predicates33832
Ref: -any?33956
Ref: -all?34276
Ref: -none?34606
Ref: -only-some?34908
Ref: -contains?35393
Ref: -same-items?35782
Ref: -is-prefix?36167
Ref: -is-suffix?36490
Ref: -is-infix?36813
Node: Partitioning37167
Ref: -split-at37355
Ref: -split-with37640
Ref: -split-on38043
Ref: -split-when38719
Ref: -separate39359
Ref: -partition39801
Ref: -partition-all40253
Ref: -partition-in-steps40681
Ref: -partition-all-in-steps41178
Ref: -partition-by41663
Ref: -partition-by-header42045
Ref: -partition-after-pred42649
Ref: -partition-before-pred43020
Ref: -partition-before-item43398
Ref: -partition-after-item43709
Ref: -group-by44015
Node: Indexing44452
Ref: -elem-index44654
Ref: -elem-indices45049
Ref: -find-index45432
Ref: -find-last-index45921
Ref: -find-indices46425
Ref: -grade-up46833
Ref: -grade-down47236
Node: Set operations47646
Ref: -union47829
Ref: -difference48271
Ref: -intersection48688
Ref: -powerset49125
Ref: -permutations49338
Ref: -distinct49638
Node: Other list operations49962
Ref: -rotate50187
Ref: -repeat50557
Ref: -cons*50820
Ref: -snoc51207
Ref: -interpose51620
Ref: -interleave51918
Ref: -zip-with52287
Ref: -zip53004
Ref: -zip-fill53810
Ref: -unzip54133
Ref: -cycle54667
Ref: -pad55040
Ref: -table55363
Ref: -table-flat56152
Ref: -first57160
Ref: -some57532
Ref: -last57841
Ref: -first-item58175
Ref: -second-item58591
Ref: -third-item58871
Ref: -fourth-item59149
Ref: -fifth-item59415
Ref: -last-item59677
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Ref: -sort60216
Ref: -list60705
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Node: Tree operations61576
Ref: -tree-seq61772
Ref: -tree-map62630
Ref: -tree-map-nodes63073
Ref: -tree-reduce63923
Ref: -tree-reduce-from64805
Ref: -tree-mapreduce65406
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Node: Threading macros67880
Ref: ->68025
Ref: ->>68516
Ref: -->69021
Ref: -as->69577
Ref: -some->70032
Ref: -some->>70406
Ref: -some-->70842
Node: Binding71313
Ref: -when-let71525
Ref: -when-let*72010
Ref: -if-let72533
Ref: -if-let*72928
Ref: -let73545
Ref: -let*79635
Ref: -lambda80575
Ref: -setq81372
Node: Side-effects82188
Ref: -each82382
Ref: -each-while82789
Ref: -each-indexed83149
Ref: -each-r83667
Ref: -each-r-while84100
Ref: -dotimes84475
Ref: -doto84778
Ref: --doto85206
Node: Destructive operations85481
Ref: !cons85654
Ref: !cdr85860
Node: Function combinators86055
Ref: -partial86329
Ref: -rpartial86725
Ref: -juxt87128
Ref: -compose87560
Ref: -applify88113
Ref: -on88560
Ref: -flip89086
Ref: -const89398
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Ref: -fixfn92165
Ref: -prodfn93728
Node: Development94796
Node: Contribute95145
Node: Changes95893
Node: Contributors98891
Node: Index100510

End Tag Table


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