elm/step0_repl.elm

   1 port module Main exposing (..)
   2
   3 import IO exposing (..)
   4 import Json.Decode exposing (decodeValue)
   5 import Platform exposing (programWithFlags)
   6
   7
   8 main : Program Flags Model Msg
   9 main =
  10     programWithFlags
  11         { init = init
  12         , update = update
  13         , subscriptions =
  14             \model -> input (decodeValue decodeIO >> Input)
  15         }
  16
  17
  18 type alias Flags =
  19     { args : List String
  20     }
  21
  22
  23 type alias Model =
  24     { args : List String
  25     }
  26
  27
  28 type Msg
  29     = Input (Result String IO)
  30
  31
  32 init : Flags -> ( Model, Cmd Msg )
  33 init flags =
  34     ( flags, readLine prompt )
  35
  36
  37 update : Msg -> Model -> ( Model, Cmd Msg )
  38 update msg model =
  39     case msg of
  40         Input (Ok (LineRead (Just line))) ->
  41             ( model, writeLine (rep line) )
  42
  43         Input (Ok LineWritten) ->
  44             ( model, readLine prompt )
  45
  46         Input (Ok (LineRead Nothing)) ->
  47             ( model, Cmd.none )
  48
  49         Input (Ok _) ->
  50             ( model, Cmd.none )
  51
  52         Input (Err msg) ->
  53             Debug.crash msg ( model, Cmd.none )
  54
  55
  56 prompt : String
  57 prompt =
  58     "user> "
  59
  60
  61 read : String -> String
  62 read ast =
  63     ast
  64
  65
  66 eval : String -> String
  67 eval ast =
  68     ast
  69
  70
  71 print : String -> String
  72 print ast =
  73     ast
  74
  75
  76 rep : String -> String
  77 rep =
  78     read >> eval >> print