elm/IO.elm

   1 port module IO
   2     exposing
   3         ( IO(..)
   4         , writeLine
   5         , readLine
   6         , readFile
   7         , input
   8         , decodeIO
   9         )
  10
  11 import Json.Decode exposing (..)
  12 import Time exposing (Time)
  13
  14
  15 {-| Output a string to stdout
  16 -}
  17 port writeLine : String -> Cmd msg
  18
  19
  20 {-| Read a line from the stdin
  21 -}
  22 port readLine : String -> Cmd msg
  23
  24
  25 {-| Read the contents of a file
  26 -}
  27 port readFile : String -> Cmd msg
  28
  29
  30 {-| Received a response for a command.
  31 -}
  32 port input : (Value -> msg) -> Sub msg
  33
  34
  35 type IO
  36     = LineRead (Maybe String)
  37     | LineWritten
  38     | FileRead String
  39     | Exception String
  40     | GotTime Time
  41
  42
  43 decodeIO : Decoder IO
  44 decodeIO =
  45     field "tag" string
  46         |> andThen decodeTag
  47
  48
  49 decodeTag : String -> Decoder IO
  50 decodeTag tag =
  51     case tag of
  52         "lineRead" ->
  53             field "line" (nullable string)
  54                 |> map LineRead
  55
  56         "lineWritten" ->
  57             succeed LineWritten
  58
  59         "fileRead" ->
  60             field "contents" string
  61                 |> map FileRead
  62
  63         "exception" ->
  64             field "message" string
  65                 |> map Exception
  66
  67         _ ->
  68             fail <|
  69                 "Trying to decode IO, but tag "
  70                     ++ tag
  71                     ++ " is not supported."