fix monad syntax bug puffnfresh#160

src/compile.js

@@ -205,10 +205,11 @@ var compileNodeWithEnv = function(n, env, opts) {
         visitBind: function() {
             var init = n.rest.slice(0, n.rest.length - 1);
             var last = n.rest[n.rest.length - 1];
+						var compiledLast = last ? compileNode(last) : "";
             return "__monad__.bind(" + compileNode(n.value) +
                 ", function(" + n.name + ") {\n" + pushIndent() +
                 _.map(init, compileNode).join(";\n" + getIndent()) + "\n" +
-                getIndent() + "return " + compileNode(last) + "\n" +
+                getIndent() + "return " + compiledLast + "\n" +
                 popIndent() + "});";
         },
         visitDo: function() {

src/grammar.js

@@ -42,7 +42,9 @@ var grammar = {
             ["doBody TERMINATOR", "$$ = $1;"]
         ],
         "doLine": [
-            ["line", "$$ = $1;"],
+            ["statement", "$$ = $1;"],
+            ["expression", n("$$ = new yy.Bind('_', $1);")],
+            ["COMMENT", n("$$ = new yy.Comment($1);")],
             ["IDENTIFIER LEFTARROW expression", n("$$ = new yy.Bind($1, $3);")],
             ["RETURN expression", n("$$ = new yy.Return($2);")]
         ],

test/CompileSpec.js

@@ -75,6 +75,9 @@ describe('compiler', function(){
         it('trace_monad.roy with expected output', function() {
             expectExecutionToHaveExpectedOutput('good/trace_monad');
         });
+        it('callbackmonad.roy with expected output', function() {
+            expectExecutionToHaveExpectedOutput('good/callbackmonad');
+        });
         it('unicode.roy with expected output', function() {
             expectExecutionToHaveExpectedOutput('good/unicode');
         });

test/fixtures/good/callbackmonad.out

@@ -0,0 +1,3 @@
+starting
+hello
+world

test/fixtures/good/callbackmonad.roy

@@ -0,0 +1,24 @@
+let callbacks = {
+  return: \x ->
+    \callback -> callback x
+  bind: \action1 f ->
+    \callback ->
+      let callback1 = \x ->
+        let action2 = f x
+        action2 callback
+      action1 callback1
+}
+
+let wait seconds = (\callback -> setTimeout callback (seconds * 1000))
+let print x = \callback -> 
+  console.log x
+  callback ()
+let nop _ = _
+
+console.log "starting"
+let program = do callbacks
+  _ <- print "hello"
+  print "world"
+
+program nop
+

test/fixtures/good/trace_monad.out

@@ -1,5 +1,6 @@
 Binding: 1
 Binding: 3
 Binding: 4
+Binding: 5
 Return: 10
 10

test/fixtures/good/trace_monad.roy

@@ -12,5 +12,6 @@ console.log (do traceMonad
   let x = 2
   y ← 3
   z ← 4
+  5
   return w + x + y + z
 )