Elm for Node.js

Main.elm

port module Main exposing (..)


type alias Input =
    { argv : List String, stdin : String }


type alias Output =
    { code : Int, stdout : String, stderr : String }


main : Program Input () ()
main =
    Platform.worker
        { init = \flags -> ( (), exit (run flags) )
        , update = \_ _ -> ( (), Cmd.none )
        , subscriptions = \_ -> Sub.none
        }


run : Input -> Output
run { stdin, argv } =
    let
        result =
            Ok "Hello word"
    in
    case result of
        Ok value ->
            Output 0 value ""

        Err error ->
            Output 1 "" ("I stopped because,\n" ++ error ++ "\n")


port exit : Output -> Cmd msg

run.js

#!/usr/bin/env node

const main = () =>
  Promise.resolve()
    .then(readStdin)
    .then(stdin => run(process.argv, stdin))
    .then(v => exit(v.code, v.stdout, v.stderr))
    .catch(e => exit(1, "", String(e)))

const run = (argv, stdin) =>
  new Promise(resolve => {
    require("./main.js")
      .Elm.Main.init({ flags: { argv, stdin } })
      .ports.exit.subscribe(resolve)
  })

const exit = (code, stdout, stderr) => {
  process.stdout.write(stdout)
  process.stderr.write(stderr)
  process.exit(code)
}

const readStdin = () =>
  new Promise(resolve => {
    let buffer = ""
    if (process.stdin.isTTY) {
      resolve(buffer)
      return
    }
    process.stdin.setEncoding("utf8")
    process.stdin.on("readable", () => {
      let chunk
      while ((chunk = process.stdin.read())) {
        buffer += chunk
      }
    })
    process.stdin.on("end", () => {
      resolve(buffer)
    })
  })

main()

run.sh

set -e
cd "${0%/*}"

elm make src/Main.elm --output main.js --optimize
clear
node run.js