Servant Elm
Generate Elm functions to query your Servant API!
Elm type generation coutesy of elm-bridge.
Installation
Servant Elm is available on Hackage.
Example
First, some language pragmas and imports.
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeOperators #-}
import Elm.Derive (defaultOptions, deriveBoth)
import Servant.API ((:>), Capture, Get, JSON)
import Servant.Elm (DefineElm (DefineElm), Proxy (Proxy), defElmImports, defElmOptions,
generateElmModuleWith)We have some Haskell-defined types and our Servant API.
data Book = Book
{ name :: String
}
deriveBoth defaultOptions ''Book
type BooksApi = "books" :> Capture "bookId" Int :> Get '[JSON] BookNow we can generate Elm functions to query the API:
main :: IO ()
main =
generateElmModuleWith
defElmOptions
[ "Generated"
, "MyApi"
]
defElmImports
"my-elm-dir"
[ DefineElm (Proxy :: Proxy Book)
]
(Proxy :: Proxy BooksApi)Let's save this as example.hs and run it:
$ stack runghc example.hs
Writing: my-elm-dir/Generated/MyApi.elm
Here's what was generated:
module Generated.MyApi exposing(..)
import Json.Decode
import Json.Encode exposing (Value)
-- The following module comes from bartavelle/json-helpers
import Json.Helpers exposing (..)
import Dict exposing (Dict)
import Set
import Http
import String
import Url.Builder
type alias Book =
{ name: String
}
jsonDecBook : Json.Decode.Decoder ( Book )
jsonDecBook =
Json.Decode.succeed (\pname -> {name = pname})
|> required "name" (Json.Decode.string)
jsonEncBook : Book -> Value
jsonEncBook val =
Json.Encode.object
[ ("name", Json.Encode.string val.name)
]
getBooksByBookId : Int -> Http.Request Book
getBooksByBookId capture_bookId =
let
params =
List.filterMap identity
(List.concat
[])
in
Http.request
{ method =
"GET"
, headers =
[]
, url =
Url.Builder.absolute
[ "books"
, capture_bookId |> String.fromInt
]
params
, body =
Http.emptyBody
, expect =
Http.expectJson <| jsonDecBook
, timeout =
Nothing
, withCredentials =
False
}See examples for a complete usage example, or take a look at
mattjbray/servant-elm-example-app (elm 0.18) or haskell-servant/example-servant-elm (elm 0.19) for an example project using this library.
Development
$ git clone https://github.com/mattjbray/servant-elm.git
$ cd servant-elm
$ stack test
$ stack test --flag servant-elm:integration
To build all examples:
$ make examples
To run an example:
$ cd examples/e2e-tests
$ elm-reactor
# Open http://localhost:8000/elm/Main.elm