Add a (debug) interactive demo

src/Bergamot/Parser.elm

@@ -26,7 +26,8 @@ variable = Parser.variable
 term : Parser (Term Metavariable)
 term = Parser.lazy (\() -> Parser.oneOf
     [ Parser.succeed IntLit |= intLit
-    , Parser.succeed Call
+    , Parser.backtrackable <|
+      Parser.succeed Call
         |= name
         |= Parser.sequence
             { start = "("
@@ -36,6 +37,8 @@ term = Parser.lazy (\() -> Parser.oneOf
             , item = term
             , trailing = Forbidden
             }
+    , Parser.succeed (\n -> Call n [])
+        |= name
     , Parser.succeed Var |= variable
     ])
 
@@ -70,3 +73,9 @@ program =
         , trailing = Mandatory
         }
     |. Parser.end
+
+run : Parser a -> String -> Maybe a
+run prs s =
+    case Parser.run prs s of
+        Ok a -> Just a
+        Err _ -> Nothing

src/Main.elm

@@ -2,6 +2,7 @@ module Main exposing (main)
 
 import Browser
 import Html exposing (Html)
+import Html.Events exposing (onInput)
 import Bergamot.Syntax exposing (..)
 import Bergamot.Search exposing (..)
 import Bergamot.Rules exposing (..)
@@ -10,20 +11,24 @@ import Maybe
 import Tuple
 import Debug
 
-type alias Model = {}
+type alias Model = { program : String }
 type alias Flags = ()
-type alias Msg = ()
+type Msg
+    = SetProgram String
 
 init : Flags -> (Model, Cmd Msg)
-init () = ({}, Cmd.none)
+init () = ({ program = "" }, Cmd.none)
 
 view : Model -> Html Msg
-view _ = Html.div [] []
+view m = Html.div []
+    [ Html.textarea [ onInput SetProgram ] []
+    , Html.p [] [ Html.text (Debug.toString (run program m.program)) ]
+    ]
 
 update : Msg -> Model -> (Model, Cmd Msg)
 update msg m =
     case msg of
-        () -> (m, Cmd.none)
+        SetProgram prog -> ({ m | program = prog }, Cmd.none)
 
 subscriptions : Model -> Sub Msg
 subscriptions _ = Sub.none