support async generators with ->>*

Also support the more verbose `async function* named-fn` option.

scripts/test

@@ -170,6 +170,11 @@
   } else {
     files.splice(files.indexOf("async.ls"), 1);
   }
+  if (testSyntax("(async function* () {})")) {
+    console.log("Testing with async generators.");
+  } else {
+    files.splice(files.indexOf("async-generators.ls"), 1);
+  }
 
   files.forEach(function(file){
     var stk, msg, m, ref, num, row, col, that, lines, line;

src/ast.ls

@@ -2003,10 +2003,11 @@ class exports.Fun extends Node
         code = [\function]
         if @async
             @ctor and @carp "a constructor can't be async"
-            @generator and @carp "a generator can't be async"
             o.in-async = true
             code.unshift 'async '
-        else if @generator
+        else if not @wrapper
+            o.in-async = false
+        if @generator
             @ctor and @carp "a constructor can't be a generator"
             o.in-generator = true
             code.push \*

src/grammar.ls

@@ -288,6 +288,8 @@ bnf =
         , -> (Fun $3, $6, false, false, false, true, false).named $1
         o 'ASYNC FUNCTION CALL( ArgList OptComma )CALL Block'
         , -> (Fun $4, $7, false, false, false, false, true).named $2
+        o 'ASYNC GENERATOR CALL( ArgList OptComma )CALL Block'
+        , -> (Fun $4, $7, false, false, false, true, true).named $2
 
         # The full complement of `if` and `unless` expressions
         o 'IF Expression Block Else'      -> L 1 2 If $2, $3, $1 is 'unless' .add-else $4

src/lexer.ls

@@ -1043,9 +1043,7 @@ character = if not JSON? then uxxxx else ->
         case 'ID'
             break unless val is 'async'
             next = tokens[i + 1]
-            switch next.0
-            | 'FUNCTION' => token.0 = 'ASYNC'
-            | 'GENERATOR' => carp 'named generator cannot be async' line
+            if next.0 in <[ FUNCTION GENERATOR ]> then token.0 = 'ASYNC'
         prev = token
         continue
 

test/async-generators.ls

@@ -0,0 +1,56 @@
+do ->
+  ag = ->>*
+    yield await Promise.resolve 1
+    yield await Promise.resolve 2
+  ai = ag!
+  ai.next!then -> eq 1 it.value
+  ai.next!then -> eq 2 it.value
+  ai.next!then -> ok it.done
+
+do ->
+  ag = ->>*
+    let x = 1
+      yield await Promise.resolve x
+      yield await Promise.resolve 2*x
+  ai = ag!
+  ai.next!then -> eq 1 it.value
+  ai.next!then -> eq 2 it.value
+  ai.next!then -> ok it.done
+
+do ->
+  async function* ag
+    yield await Promise.resolve 1
+    yield await Promise.resolve 2
+  ai = ag!
+  ai.next!then -> eq 1 it.value
+  ai.next!then -> eq 2 it.value
+  ai.next!then -> ok it.done
+
+# yield from
+do ->
+  first = !->>*
+    i = await Promise.resolve 0
+    loop => yield i++
+  second = !->>* yield from first!
+  list = second!
+  for let i to 3 then list.next!then -> eq it.value, i
+
+# This tests that yield and await still work inside the generated closure.
+do ->
+  ag = ->>* [i = 0] ++ while i < 3 then yield await Promise.resolve i++
+  ai = ag!
+  ai.next!   .then -> eq 0 it.value
+  ai.next 10 .then -> eq 1 it.value
+  ai.next 20 .then -> eq 2 it.value
+  ai.next 30 .then ->
+    ok it.done
+    eq '0,10,20,30' ''+it.value
+
+# This tests that the inner function clears both the async and generator flags
+# for the closure that is generated within it.
+do ->
+  ag = ->>* -> [i = 0] ++ while i < 3 then i++
+  ai = ag!
+  ai.next!then ->
+    ok it.done
+    eq '0,0,1,2' ''+it.value!

test/async.ls

@@ -185,9 +185,6 @@ do ->
   y <- obj2.bound!then
   eq y, 3
 
-# check that ->>* results in an error at compile time
-compile-throws "a generator can't be async" 1 '->>* 3'
-
 # [LiveScript#1019](https://github.com/gkz/LiveScript/issues/1019)
 # in `let` blocks
 do ->