repl.js

import 'colors'
import { Elm } from './Main.elm'
import * as REPL from 'repl'

// I don't know if this actually does anything. I set this when I was fucking around
// trying to support `shift+Enter` but that didn't work so here we are....
process.stdin.setRawMode(true)
process.stdin.setEncoding('utf8')

const res = s => console.log('    : ' + s.grey)
const err = s => console.log('    : ' + s.red)

const app = Elm.Main.init()

const send = input => {
  app.ports.stdOut.subscribe(
    function writeStdOut (output) {
      app.ports.stdOut.unsubscribe(writeStdOut)
      res(output.split('\n').filter(line => line !== '').join('\n'))

      repl.setPrompt('λ ')
      repl.displayPrompt(false)
    }
  )

  app.ports.stdErr.subscribe(
    function writeStdErr (output) {
      app.ports.stdErr.unsubscribe(writeStdErr)
      err(output.split('\n').filter(line => line !== '').join('\n'))

      repl.setPrompt('λ ')
      repl.displayPrompt(false)
    }
  )

  app.ports.stdIn.send(input)
}

// The buffer stores the current lines if we're in multi-line input mode. This
// happens automatically when the input ends with `\`.
const buffer = []
const evaluate = (input, callback, repl) => {
  if (input.endsWith('\\\n')) {
    buffer.push(input.substring(0, input.length - 2))
    repl.setPrompt('|   ') // Update the prompt to indicate mutli-line mode
    repl.displayPrompt(false) // Reset the cursor position

    return
  }

  if (input === '') return

  buffer.push(input)
  send(buffer.join('\n'))
  buffer.length = 0
}

const repl = REPL.start({
  prompt: 'λ ',
  eval (input, context, file, callback) {
    evaluate(input, callback, repl)
  },
  useColors: true,
  preview: true
})