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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
**************
Its available on 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. Heres 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 occurrences 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
arent 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 occurrence 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 occurrence 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 thats 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 #'odd? '())
⇒ '()
(-partition-after-pred #'odd? '(1))
⇒ '((1))
(-partition-after-pred #'odd? '(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 #'odd? '())
⇒ '()
(-partition-before-pred #'odd? '(1))
⇒ '((1))
(-partition-before-pred #'odd? '(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 thats 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 thats 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 thats 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 thats
non-nil.
Alias: -uniq
(-distinct '())
⇒ '()
(-distinct '(1 2 2 4))
⇒ '(1 2 4)
(-distinct '(t t t))
⇒ '(t)

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.
Use -zip-lists (*note -zip-lists::) if you need the return value
to always be a list of lists.
Alias: -zip-pair
See also: -zip-lists (*note -zip-lists::)
(-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 5) '(6))
⇒ '((1 3 6))
-- Function: -zip-lists (&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.
The return value is always list of lists, which is a difference
from -zip-pair which returns a cons-cell in case two input lists
are provided.
See also: -zip (*note -zip::)
(-zip-lists '(1 2 3) '(4 5 6))
⇒ '((1 4) (2 5) (3 6))
(-zip-lists '(1 2 3) '(4 5 6 7))
⇒ '((1 4) (2 5) (3 6))
(-zip-lists '(1 2) '(3 4 5) '(6))
⇒ '((1 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).
Note in particular that calling this on a list of two lists will
return a list of cons-cells such that the aboce identity works.
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))
(-unzip '((1 2) (3 4)))
⇒ '((1 . 3) (2 . 4))
-- 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 its possible. You can use this
to skip over entries you dont 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
satisfied:
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 comparison 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. Theres 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 dont 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.