Elm Bridge

Intro

Hackage: elm-bridge

Building the bridge from Haskell to Elm and back. Define types once, use on both sides and enjoy easy (de)serialisation. Cheers!

This version of the package only supports Elm 0.19. The generated code works with Elm 0.19.1 and Elm 0.19.2, and the end-to-end tests run on Elm 0.19.2. Version 0.5.2 supports Elm 0.18, and Version 0.3.0.2 supports Elm 0.16 and Elm 0.17.

Note that the bartavelle/json-helpers package, with version >= 1.2.0, is expected by the generated Elm modules.

Usage

{-# LANGUAGE TemplateHaskell #-}
import Elm.Derive
import Elm.Module

import Data.Proxy

data Foo
   = Foo
   { f_name :: String
   , f_blablub :: Int
   } deriving (Show, Eq)

deriveBoth defaultOptions ''Foo

main :: IO ()
main =
    putStrLn $ makeElmModule "Foo"
    [ DefineElm (Proxy :: Proxy Foo)
    ]

Output will be:

module Foo where

import Json.Decode
import Json.Decode exposing ((:=))
import Json.Encode
import Json.Helpers exposing (..)


type alias Foo  =
   { f_name: String
   , f_blablub: Int
   }

jsonDecFoo : Json.Decode.Decoder ( Foo )
jsonDecFoo =
   ("f_name" := Json.Decode.string) `Json.Decode.andThen` \pf_name ->
   ("f_blablub" := Json.Decode.int) `Json.Decode.andThen` \pf_blablub ->
   Json.Decode.succeed {f_name = pf_name, f_blablub = pf_blablub}

jsonEncFoo : Foo -> Value
jsonEncFoo  val =
   Json.Encode.object
   [ ("f_name", Json.Encode.string val.f_name)
   , ("f_blablub", Json.Encode.int val.f_blablub)
   ]

The default type conversion rules (see Elm.Module.defaultAlterations) convert Haskell types that do not exist in Elm. E.g. Text becomes String, Map String v becomes Dict String v and Either a b becomes Result a b.

Also, there are functions Elm.Json.stringSerForSimpleAdt and Elm.Json.stringParserForSimpleAdt to generate functions for your non-JSON ADT types.

For more usage examples check the tests or the examples dir.

Install

Haskell

• Using cabal: cabal install elm-bridge
• From Source: git clone https://github.com/agrafix/elm-bridge.git && cd elm-bridge && cabal install

Elm

• elm package install bartavelle/json-helpers

or, for Elm 0.19:

• elm install bartavelle/json-helpers

Contribute

To run the tests, you need stack, node, Elm 0.19.2 and elm-test 0.19.2:

stack test
$(stack path --dist-dir)/build/end-to-end-tests/end-to-end-tests test/current-end-to-end/tests/MyTests.elm
cd test/current-end-to-end && npx [email protected]

The second command generates an Elm module with tests that decode and encode values that aeson produced. The third command compiles and runs these tests.

Pull requests are welcome! Please consider creating an issue beforehand, so we can discuss what you would like to do. Code should be written in a consistent style throughout the project. Avoid whitespace that is sensible to conflicts. (E.g. alignment of = signs in functions definitions) Note that by sending a pull request you agree that your contribution can be released under the BSD3 License as part of the elm-bridge package or related packages.