Make 'language term' just a custom mode

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

src/Bergamot/ObjectLanguage.elm

@@ -1,9 +1,10 @@
-module Bergamot.ObjectLanguage exposing (..)
+port module Bergamot.ObjectLanguage exposing (..)
 
-import Bergamot.Syntax as Syntax exposing (Metavariable)
+import Bergamot.Syntax as Syntax exposing (toString)
 import Bergamot.Parser exposing (strLit)
 
-import Parser exposing (Parser, Trailing(..), (|.), (|=))
+import Platform exposing (worker)
+import Parser exposing (Parser, Trailing(..), (|.), (|=), run)
 import Set
 
 type Type
@@ -135,7 +136,7 @@ exprBasic = Parser.lazy <| \() -> Parser.oneOf
     , parenthed expr
     ]
 
-typeToTerm : Type -> Syntax.Term Metavariable
+typeToTerm : Type -> Syntax.Term ()
 typeToTerm t =
     case t of
         TInt -> Syntax.Call "number" []
@@ -143,7 +144,7 @@ typeToTerm t =
         TPair t1 t2 -> Syntax.Call "tpair" [ typeToTerm t1, typeToTerm t2 ]
         TArr t1 t2 -> Syntax.Call "tarr" [ typeToTerm t1, typeToTerm t2 ]
 
-exprToTerm : Expr -> Syntax.Term Metavariable
+exprToTerm : Expr -> Syntax.Term ()
 exprToTerm e =
     case e of
         IntLit i -> Syntax.Call "lit" [Syntax.IntLit i]
@@ -156,3 +157,36 @@ exprToTerm e =
         Abs s t ep -> Syntax.Call "abs" [Syntax.Call s [], typeToTerm t, exprToTerm ep]
         App e1 e2 -> Syntax.Call "app" [exprToTerm e1, exprToTerm e2]
         Ref x -> Syntax.Call "var" [Syntax.Call x []]
+
+-- Receives requests from JS code to apply the parser
+port parseString : (String -> msg) -> Sub msg
+
+-- Used to send the result of parsing back to JS
+port parsedString : { string : String, term : Maybe String } -> Cmd msg
+
+type Msg = ParseString String
+type alias Model = ()
+type alias Flags = ()
+
+init : Flags -> (Model, Cmd Msg)
+init _ = ((), Cmd.none)
+
+update : Msg -> Model -> (Model, Cmd Msg)
+update (ParseString s) _ =
+    case run topLevelExpr s of
+        Ok e ->
+            ( ()
+            , parsedString
+                { string = s
+                , term =
+                    exprToTerm e
+                    |> toString (\_ -> "")
+                    |> Just
+                }
+            )
+        Err _ -> ((), parsedString { string = s, term = Nothing })
+
+subscriptions : Model -> Sub Msg
+subscriptions _ = parseString ParseString
+
+main = worker { init = init, update = update, subscriptions = subscriptions }