Create Elm classes and JSON decoders from Haskell DataTypes.
Elm Export is available on Hackage.
To use this library, you must first make the types you want to export
implement ElmType. This is easy. Just derive Generic, and then
we can automatically generate the ElmType instance for you. Here's
an example with a Person type:
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DeriveAnyClass #-}
module Db where
import Elm
import GHC.Generics
data Person = Person
{ id :: Int
, name :: Maybe String
} deriving (Show, Eq, Generic, ElmType)That's it for the type. Now you'll want to write a main that generates the Elm source code:
module Main where
import Data.Proxy
import Db
import Elm
spec :: Spec
spec =
Spec
["Db", "Types"]
[ "import Json.Decode exposing (..)"
, "import Json.Decode.Pipeline exposing (..)"
, toElmTypeSource (Proxy :: Proxy Person)
, toElmDecoderSource (Proxy :: Proxy Person)
]
main :: IO ()
main = specsToDir [spec] "some/where/output"Run this and the directory some/where/output will be created, and
under that the Elm source file Db/Types.elm will be found.
All the hard work here is done by toElmTypeSource and
toElmDecoderSource. The Spec code is just wrapping to make it easy
to create a complete Elm file from the meat that ElmType gives
you.
The decoders we produce require these extra Elm packages installed:
elm package install NoRedInk/elm-decode-pipeline
elm package install krisajenkins/elm-extsYou will need Stack.
stack buildstack test --file-watch- Renamed
ToElmTypetoElmType, for brevity.
- Added Encoders (thanks to Matthew Bray)
- Initial release.
Alpha. The author is using it in production, but it is not yet expected to work for every reasonable case.
There are some Haskell datatypes that cannot be represented in Elm. Obviously we will not support those. But there are some which are legal Haskell and legal Elm, but we do not yet generate. Please send examples, PRs and code-suggestions!
Copyright © 2015-2017 Kris Jenkins
Distributed under the Eclipse Public License.
Elm Bridge is a different implementation of the same goal. That project uses Template Haskell, this one uses GHC Generics.