Elm Export

Create Elm classes and JSON decoders from Haskell DataTypes.

Installation

Usage

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 =
  moduleSpec ["Db", "Types"] $ do
    require "Date exposing (Date)"
    renderType (Proxy :: Proxy Person)
    renderDecoder (Proxy :: Proxy Person)
    renderEncoder (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.

Required Elm Packages

The decoders we produce require these extra Elm packages installed:

elm package install NoRedInk/elm-decode-pipeline
elm package install krisajenkins/elm-exts

Development

You will need Stack.

Building

stack build

Testing

stack test --file-watch

Contribution Guide

Development happens on the devel branch. Pull requests target this branch.

Generated Elm code adheres to the elm-format style.

JSON encoders and decoders match the default behavior of Aeson.

Change Log

V0.6.x

Updated to Elm 0.18.

V0.5.x

???

V0.4.x

???

V0.3.0.0

Renamed ToElmType to ElmType, for brevity.

V0.2.0.0

Added Encoders (thanks to Matthew Bray)

V0.1.0.0

Initial release.

Status

Beta. Several people are using it in production, reliably, but it is not yet expected to work for every reasonable datatype.

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!

Contributors

License

Distributed under the Eclipse Public License.

jcberentsen/elm-export