closes #75; implemented after-loop else clause

lib/ast.js

@@ -1591,7 +1591,7 @@ exports.Assign = Assign = (function(_super){
     lvar = left instanceof Var;
     sign = op.replace(':', '');
     name = (left.front = true, left).compile(o, LEVEL_LIST);
-    code = !o.level && right instanceof While && (lvar || left.isSimpleAccess())
+    code = !o.level && right instanceof While && !right['else'] && (lvar || left.isSimpleAccess())
       ? (res = o.scope.temporary('res')) + " = [];\n" + this.tab + right.makeReturn(res).compile(o) + "\n" + this.tab + name + " " + sign + " " + o.scope.free(res)
       : (name + " " + sign + " ") + (right.assigned = true, right).compile(o, LEVEL_LIST);
     if (lvar) {
@@ -2392,7 +2392,7 @@ exports.While = While = (function(_super){
       this.test = test;
     }
   }
-  prototype.children = ['test', 'body', 'update'];
+  prototype.children = ['test', 'body', 'update', 'else'];
   prototype.aSource = 'test';
   prototype.aTargets = ['body', 'update'];
   prototype.show = function(){
@@ -2419,6 +2419,10 @@ exports.While = While = (function(_super){
     }
     return this;
   };
+  prototype.addElse = function($else){
+    this['else'] = $else;
+    return this;
+  };
   prototype.makeReturn = function(it){
     if (it) {
       this.body.makeReturn(it);
@@ -2443,7 +2447,7 @@ exports.While = While = (function(_super){
     return head + ') {' + this.compileBody((o.indent += TAB, o));
   };
   prototype.compileBody = function(o, potest){
-    var lines, ret, code, last, res, that;
+    var lines, ret, code, last, res, run, that;
     lines = this.body.lines;
     code = ret = '';
     if (this.returns) {
@@ -2452,13 +2456,22 @@ exports.While = While = (function(_super){
       }
       ret = "\n" + this.tab + "return " + (res || '[]') + ";";
     }
+    if (this['else']) {
+      lines.unshift(JS((run = o.scope.temporary('run')) + " = true;"));
+    }
     if (that = this.body.compile(o, LEVEL_TOP)) {
       code += "\n" + that + "\n" + this.tab;
     }
     code += '}';
     if (potest) {
       code += " while (" + potest.compile((o.tab = this.tab, o), LEVEL_PAREN) + ");";
     }
+    if (run) {
+      if (this.returns) {
+        this['else'].makeReturn();
+      }
+      code += " if (!" + run + ") " + this.compileBlock(o, this['else']);
+    }
     return code + ret;
   };
   prototype.pluckDirectCalls = function(o){

lib/grammar.js

@@ -129,8 +129,10 @@ bnf = {
       return $1.addElse($3);
     }), o('Expression POST_IF Expression', function(){
       return If($3, $1, $2 === 'unless');
-    }), o('LoopHead   Block', function(){
+    }), o('LoopHead Block', function(){
       return $1.addBody($2);
+    }), o('LoopHead Block ELSE Block', function(){
+      return $1.addBody($2).addElse($4);
     }), o('Expression LoopHead', function(){
       return $2.addBody(Block($1));
     }), o('DO Block WHILE Expression', function(){

src/ast.co

@@ -934,7 +934,7 @@ class exports.Assign extends Node
     lvar = left instanceof Var
     sign = op.replace \: ''
     name = (left <<< {+front})compile o, LEVEL_LIST
-    code = if not o.level and right instanceof While and
+    code = if not o.level and right instanceof While and not right.else and
               (lvar or left.isSimpleAccess())
       # Optimize `a = while ...`.
       """#{ res = o.scope.temporary \res } = [];
@@ -1447,7 +1447,7 @@ class exports.While extends Node
     # `while true` `until false` => `for (;;)`
     import {test} if @post or test.value is not ''+!un
 
-  children: <[ test body update ]>
+  children: <[ test body update else ]>
 
   aSource: \test, aTargets: <[ body update ]>
 
@@ -1462,6 +1462,8 @@ class exports.While extends Node
     body.lines.length = 0 if top?verb is \continue and not top.label
     this
 
+  addElse: (@else) -> this
+
   makeReturn: ->
     if it
     then @body.makeReturn it
@@ -1484,9 +1486,13 @@ class exports.While extends Node
       if (last = lines[*-1]) and last not instanceof Throw
         lines[*-1] = last.makeReturn res = o.scope.assign \_results '[]'
       ret = "\n#{@tab}return #{ res or '[]' };"
+    lines.unshift JS "#{ run = o.scope.temporary \run } = true;" if @else
     code += "\n#that\n#{@tab}" if @body.compile o, LEVEL_TOP
     code += \}
     code += " while (#{ potest.compile o<<<{@tab} LEVEL_PAREN });" if potest
+    if run
+      @else.makeReturn() if @returns
+      code += " if (!#run) #{ @compileBlock o, @else }"
     code + ret
 
   pluckDirectCalls: (o) ->

src/grammar.co

@@ -172,7 +172,8 @@ bnf =
 
     # Loops can either be normal, with a block of expressions
     # to execute, or postfix, with a single expression.
-    o 'LoopHead   Block'    -> $1.addBody $2
+    o 'LoopHead Block'            -> $1.addBody $2
+    o 'LoopHead Block ELSE Block' -> $1.addBody $2 .addElse $4
     o 'Expression LoopHead' -> $2.addBody Block $1
     o 'DO Block WHILE Expression'
     , -> new While($4, $3 is \until, true)addBody $2

test/loop.co

@@ -266,3 +266,17 @@ a = [1 2 3]
 b = []
 continue while a.pop(), b.push that
 eq '3,2,1' ''+b
+
+
+### `else` clause
+for cond of [true false]
+  while cond
+    break
+  else
+    ok not cond
+
+r = for i til 1 then i else [9]
+eq 0 r.0
+
+r = for i til 0 then i else [9]
+eq 9 r.0