adding conditional while loops with while ... when

lib/grammar.js

@@ -414,13 +414,20 @@
         return new ParentheticalNode($2);
       })
     ],
+    // The condition for a while loop.
+    WhileSource: [o("WHILE Expression", function() {
+        return new WhileNode($2);
+      }), o("WHILE Expression WHEN Expression", function() {
+        return new WhileNode($2, {
+          filter: $4
+        });
+      })
+    ],
     // The while loop. (there is no do..while).
-    While: [o("WHILE Expression Block", function() {
-        return new WhileNode($2, $3);
-      }), o("WHILE Expression", function() {
-        return new WhileNode($2, null);
-      }), o("Expression WHILE Expression", function() {
-        return new WhileNode($3, Expressions.wrap([$1]));
+    While: [o("WhileSource Block", function() {
+        return $1.add_body($2);
+      }), o("Expression WhileSource", function() {
+        return $2.add_body($1);
       })
     ],
     // Array comprehensions, including guard and current index.

lib/nodes.js

@@ -891,8 +891,13 @@
   // it, all other loops can be manufactured.
   WhileNode = (exports.WhileNode = inherit(Node, {
     type: 'While',
-    constructor: function constructor(condition, body) {
-      this.children = [(this.condition = condition), (this.body = body)];
+    constructor: function constructor(condition, opts) {
+      this.children = [(this.condition = condition)];
+      this.filter = opts && opts.filter;
+      return this;
+    },
+    add_body: function add_body(body) {
+      this.children.push((this.body = body));
       return this;
     },
     top_sensitive: function top_sensitive() {
@@ -909,13 +914,18 @@
       if (!top) {
         rvar = o.scope.free_variable();
         set = this.idt() + rvar + ' = [];\n';
-        this.body = PushNode.wrap(rvar, this.body);
+        if (this.body) {
+          this.body = PushNode.wrap(rvar, this.body);
+        }
       }
       post = returns ? '\n' + this.idt() + 'return ' + rvar + ';' : '';
       pre = set + this.idt() + 'while (' + cond + ')';
       if (!this.body) {
         return pre + ' null;' + post;
       }
+      if (this.filter) {
+        this.body = Expressions.wrap([new IfNode(this.filter, this.body)]);
+      }
       return pre + ' {\n' + this.body.compile(o) + '\n' + this.idt() + '}' + post;
     }
   }));

src/grammar.coffee

@@ -360,11 +360,16 @@ grammar: {
     o "( Expression )",                         -> new ParentheticalNode($2)
   ]
 
+  # The condition for a while loop.
+  WhileSource: [
+    o "WHILE Expression",                       -> new WhileNode($2)
+    o "WHILE Expression WHEN Expression",       -> new WhileNode($2, {filter : $4})
+  ]
+
   # The while loop. (there is no do..while).
   While: [
-    o "WHILE Expression Block",                 -> new WhileNode($2, $3)
-    o "WHILE Expression",                       -> new WhileNode($2, null)
-    o "Expression WHILE Expression",            -> new WhileNode($3, Expressions.wrap([$1]))
+    o "WhileSource Block",                      -> $1.add_body $2
+    o "Expression WhileSource",                 -> $2.add_body $1
   ]
 
   # Array comprehensions, including guard and current index.
@@ -384,10 +389,8 @@ grammar: {
   ForSource: [
     o "IN Expression",                          -> {source:   $2}
     o "OF Expression",                          -> {source:   $2, object: true}
-    o "ForSource WHEN Expression",              ->
-      $1.filter: $3; $1
-    o "ForSource BY Expression",                ->
-      $1.step:   $3; $1
+    o "ForSource WHEN Expression",              -> $1.filter: $3; $1
+    o "ForSource BY Expression",                -> $1.step:   $3; $1
   ]
 
   # Switch/When blocks.
@@ -406,8 +409,7 @@ grammar: {
   When: [
     o "LEADING_WHEN SimpleArgs Block",          -> new IfNode($2, $3, null, {statement: true})
     o "LEADING_WHEN SimpleArgs Block TERMINATOR", -> new IfNode($2, $3, null, {statement: true})
-    o "Comment TERMINATOR When",                ->
-      $3.comment: $1; $3
+    o "Comment TERMINATOR When",                -> $3.comment: $1; $3
   ]
 
   # The most basic form of "if".

src/nodes.coffee

@@ -701,8 +701,13 @@ SplatNode: exports.SplatNode: inherit Node, {
 WhileNode: exports.WhileNode: inherit Node, {
   type: 'While'
 
-  constructor: (condition, body) ->
-    @children:[@condition: condition, @body: body]
+  constructor: (condition, opts) ->
+    @children:[@condition: condition]
+    @filter: opts and opts.filter
+    this
+
+  add_body: (body) ->
+    @children.push @body: body
     this
 
   top_sensitive: ->
@@ -718,10 +723,11 @@ WhileNode: exports.WhileNode: inherit Node, {
     if not top
       rvar:     o.scope.free_variable()
       set:      @idt() + rvar + ' = [];\n'
-      @body:    PushNode.wrap(rvar, @body)
+      @body:    PushNode.wrap(rvar, @body) if @body
     post:       if returns then '\n' + @idt() + 'return ' + rvar + ';' else ''
     pre:        set + @idt() + 'while (' + cond + ')'
     return pre + ' null;' + post if not @body
+    @body:      Expressions.wrap([new IfNode(@filter, @body)]) if @filter
     pre + ' {\n' + @body.compile(o) + '\n' + @idt() + '}' + post
 
 }

test/test_literals.coffee

@@ -26,12 +26,6 @@ reg: /\\/
 ok reg(str) and str is '\\'
 
 
-i: 10
-while i -= 1
-
-ok i is 0
-
-
 money$: 'dollars'
 
 ok money$ is 'dollars'

test/test_while.coffee

@@ -1,9 +1,3 @@
-i: 100
-while i -= 1
-
-ok i is 0
-
-
 i: 5
 list: while i -= 1
   i * 2
@@ -25,4 +19,12 @@ results: while func 1
   assert()
   i
 
-ok results.join(' ') is '4 3 2 1'
+ok results.join(' ') is '4 3 2 1'
+
+
+i: 10
+results: while i -= 1 when i % 2 is 0
+  i * 2
+
+ok results.join(' ') is '16 12 8 4'
+