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108 lines
2.0 KiB
Elm
108 lines
2.0 KiB
Elm
port module Main exposing (..)
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import IO exposing (..)
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import Json.Decode exposing (decodeValue)
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import Platform exposing (programWithFlags)
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import Types exposing (MalExpr(..))
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import Reader exposing (readString)
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import Printer exposing (printString)
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import Utils exposing (maybeToList)
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main : Program Flags Model Msg
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main =
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programWithFlags
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{ init = init
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, update = update
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, subscriptions =
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\model -> input (decodeValue decodeIO >> Input)
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}
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type alias Flags =
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{ args : List String
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}
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type alias Model =
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{ args : List String
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}
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type Msg
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= Input (Result String IO)
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init : Flags -> ( Model, Cmd Msg )
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init flags =
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( flags, readLine prompt )
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update : Msg -> Model -> ( Model, Cmd Msg )
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update msg model =
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case msg of
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Input (Ok (LineRead (Just line))) ->
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case rep line of
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Just out ->
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( model, writeLine out )
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Nothing ->
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( model, readLine prompt )
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Input (Ok LineWritten) ->
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( model, readLine prompt )
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Input (Ok (LineRead Nothing)) ->
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( model, Cmd.none )
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Input (Ok io) ->
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Debug.crash "unexpected IO received: " io
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Input (Err msg) ->
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Debug.crash msg ( model, Cmd.none )
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prompt : String
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prompt =
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"user> "
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{-| read can return three things:
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Ok (Just expr) -> parsed okay
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Ok Nothing -> empty string (only whitespace and/or comments)
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Err msg -> parse error
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-}
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read : String -> Result String (Maybe MalExpr)
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read =
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readString
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eval : MalExpr -> MalExpr
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eval ast =
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ast
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print : MalExpr -> String
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print =
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printString True
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{-| Read-Eval-Print
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-}
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rep : String -> Maybe String
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rep =
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let
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formatResult result =
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case result of
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Ok optStr ->
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optStr
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Err msg ->
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Just msg
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in
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readString
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>> Result.map (Maybe.map (eval >> print))
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>> formatResult
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