* Load imports recursively This is the big change that enables us to implement 'semi-semantic' caching. * Use `throwM` instead of `liftIO . throwIO` * Fix build with __GHCJS__ * Fix exceptions in Dhall.Import * Fix dhall-lsp-server * Revert exception behaviour on typecheck errors This is one for a separate pull request! * Make sure loadImportFresh returns alpha-normal expression As caught by @Gabriel439, `loadImportFresh` violated the invariant that `ImportSemantics` should be alpha-beta-normal. This fix also means that we don't have to alpha-normalise again in `loadImportWithSemanticCache`. * Remove old comment * Fix regression test for issue 216 Turns out the test was testing the wrong thing, because it was pretty-printing an import. This worked previously because when importing uncached expressions we would not alpha-normalise them. * Restore `dhall freeze` bevhaviour Newly frozen imports should also be present in the cache. |
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.. | ||
benchmark | ||
dhall | ||
dhall-lang@f4ee1fb8f8 | ||
doctest | ||
examples | ||
src | ||
tests | ||
CHANGELOG.md | ||
default.nix | ||
dhall.cabal | ||
LICENSE | ||
README.md | ||
Setup.hs | ||
shell.nix |
dhall
For installation or development instructions, see:
Full documentation here:
Introduction
Dhall is a programmable configuration language that is not Turing-complete
You can think of Dhall as: JSON + functions + types + imports
Motivation
"Why not configure my program using JSON or YAML?"
JSON or YAML are suitable for small configuration files, but larger configuration files with complex schemas require programming language features to reduce repetition. Otherwise, the repetitive configuration files become error-prone and difficult to maintain/migrate.
This post explains in more detail the motivation behind programmable configuration files:
"Why not configure my program using Haskell code?"
You probably don't want to rebuild your program every time you make a configuration change. Recompilation is slow and requires the GHC toolchain to be installed anywhere you want to make configuration changes.
Example
Given this Haskell program saved to example.hs
:
-- example.hs
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE OverloadedStrings #-}
import Dhall
data Example = Example { foo :: Integer, bar :: Vector Double }
deriving (Generic, Show)
instance Interpret Example
main :: IO ()
main = do
x <- input auto "./config"
print (x :: Example)
... which reads in this configuration file:
$ cat ./config
{ foo = 1
, bar = ./bar
}
... which in turn references this other file:
$ cat ./bar
[3.0, 4.0, 5.0]
... you can interpret the Haskell program like this:
$ nix-shell ../nix/test-dhall.nix
[nix-shell]$ runghc example.hs
Example {foo = 1, bar = [3.0,4.0,5.0]}
You can also interpret Dhall programs directly using the installed command-line compiler:
$ dhall
List/head Double ./bar
<Ctrl-D>
Optional Double
Some 3.0
... and you can reference remote expressions or functions by their URL, too:
$ dhall
let null = https://raw.githubusercontent.com/dhall-lang/Prelude/35deff0d41f2bf86c42089c6ca16665537f54d75/List/null
in null Double ./bar
<Ctrl-D>
Bool
False
Now go read the Dhall tutorial to learn more.
Standard-compatibility table
Haskell package version | Supported standard version |
---|---|
1.20.* |
5.0.0 |
1.19.* |
4.0.0 |
1.18.* |
3.0.0 |
1.17.* |
2.0.0 |
1.16.* |
1.0.0 |