From 6b4e437c93715a08b9f05b8423a953dda3a10a93 Mon Sep 17 00:00:00 2001
From: Jeremy Ashkenas <jashkenas@gmail.com>
Date: Wed, 27 Oct 2010 22:50:20 -0400
Subject: [PATCH] CoffeeScript now compiled 'undefined' as 'void 0'

---
 lib/browser.js     |  2 +-
 lib/cake.js        |  2 +-
 lib/command.js     |  8 ++++----
 lib/grammar.js     |  2 +-
 lib/lexer.js       | 12 ++++++------
 lib/nodes.js       | 39 +++++++++++++++++++++------------------
 lib/parser.js      |  2 +-
 lib/repl.js        |  2 +-
 lib/rewriter.js    | 18 +++++++++---------
 lib/scope.js       |  4 ++--
 src/grammar.coffee | 23 ++++++++++-------------
 src/lexer.coffee   | 12 ++++++------
 src/nodes.coffee   |  7 ++++---
 13 files changed, 67 insertions(+), 66 deletions(-)

diff --git a/lib/browser.js b/lib/browser.js
index 075f6b43..b2eae701 100644
--- a/lib/browser.js
+++ b/lib/browser.js
@@ -22,7 +22,7 @@
       xhr.overrideMimeType('text/plain');
     }
     xhr.onreadystatechange = function() {
-      return xhr.readyState === 4 ? CoffeeScript.run(xhr.responseText, options) : undefined;
+      return xhr.readyState === 4 ? CoffeeScript.run(xhr.responseText, options) : void 0;
     };
     return xhr.send(null);
   };
diff --git a/lib/cake.js b/lib/cake.js
index 4ff2f4cb..7070d121 100755
--- a/lib/cake.js
+++ b/lib/cake.js
@@ -65,7 +65,7 @@
       desc = task.description ? "# " + task.description : '';
       console.log("cake " + name + spaces + " " + desc);
     }
-    return switches.length ? console.log(oparse.help()) : undefined;
+    return switches.length ? console.log(oparse.help()) : void 0;
   };
   missingTask = function(task) {
     console.log("No such task: \"" + task + "\"");
diff --git a/lib/command.js b/lib/command.js
index 61970393..2eb7c03b 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -74,7 +74,7 @@
               fs.readFile(source, function(err, code) {
                 return compileScript(source, code.toString(), base);
               });
-              return opts.watch ? watch(source, base) : undefined;
+              return opts.watch ? watch(source, base) : void 0;
             }
           });
         });
@@ -110,7 +110,7 @@
       } else {
         t.output = CoffeeScript.compile(t.input, t.options);
         CoffeeScript.emit('success', task);
-        return o.print ? console.log(t.output.trim()) : o.compile ? writeJs(t.file, t.output, base) : o.lint ? lint(t.file, t.output) : undefined;
+        return o.print ? console.log(t.output.trim()) : o.compile ? writeJs(t.file, t.output, base) : o.lint ? lint(t.file, t.output) : void 0;
       }
     } catch (err) {
       CoffeeScript.emit('failure', err, task);
@@ -129,7 +129,7 @@
     code = '';
     stdin = process.openStdin();
     stdin.on('data', function(buffer) {
-      return buffer ? code += buffer.toString() : undefined;
+      return buffer ? code += buffer.toString() : void 0;
     });
     return stdin.on('end', function() {
       return compileScript('stdio', code);
@@ -163,7 +163,7 @@
         js = ' ';
       }
       return fs.writeFile(jsPath, js, function(err) {
-        return err ? console.log(err.message) : opts.compile && opts.watch ? console.log("Compiled " + source) : undefined;
+        return err ? console.log(err.message) : opts.compile && opts.watch ? console.log("Compiled " + source) : void 0;
       });
     };
     return path.exists(dir, function(exists) {
diff --git a/lib/grammar.js b/lib/grammar.js
index 6763eb0a..9d6e4394 100644
--- a/lib/grammar.js
+++ b/lib/grammar.js
@@ -66,7 +66,7 @@
       }), o('REGEX', function() {
         return new Literal($1);
       }), o('BOOL', function() {
-        return new Literal($1);
+        return new Literal($1 === 'undefined' ? 'void 0' : $1);
       })
     ],
     Assign: [
diff --git a/lib/lexer.js b/lib/lexer.js
index 0d2b6b20..59b76736 100644
--- a/lib/lexer.js
+++ b/lib/lexer.js
@@ -94,7 +94,7 @@
         if (COFFEE_ALIASES.hasOwnProperty(id)) {
           id = COFFEE_ALIASES[id];
         }
-        tag = id === '!' ? 'UNARY' : id === '==' || id === '!=' ? 'COMPARE' : id === '&&' || id === '||' ? 'LOGIC' : id === 'true' || id === 'false' || id === 'null' ? 'BOOL' : tag;
+        tag = id === '!' ? 'UNARY' : id === '==' || id === '!=' ? 'COMPARE' : id === '&&' || id === '||' ? 'LOGIC' : id === 'true' || id === 'false' || id === 'null' || id === 'undefined' ? 'BOOL' : tag;
       }
       this.token(tag, id);
       if (colon) {
@@ -228,7 +228,7 @@
         tokens.push(['+', '+']);
       }
       tokens.pop();
-      if (((_ref3 = tokens[0]) != null ? _ref3[0] : undefined) !== 'STRING') {
+      if (((_ref3 = tokens[0]) != null ? _ref3[0] : void 0) !== 'STRING') {
         this.tokens.push(['STRING', '""'], ['+', '+']);
       }
       (_this = this.tokens).push.apply(_this, tokens);
@@ -277,7 +277,7 @@
       var dent, len;
       while (moveOut > 0) {
         len = this.indents.length - 1;
-        if (this.indents[len] === undefined) {
+        if (this.indents[len] === void 0) {
           moveOut = 0;
         } else if (this.indents[len] === this.outdebt) {
           moveOut -= this.outdebt;
@@ -357,7 +357,7 @@
         tag = 'UNARY';
       } else if (__indexOf.call(SHIFT, value) >= 0) {
         tag = 'SHIFT';
-      } else if (__indexOf.call(LOGIC, value) >= 0 || value === '?' && (prev != null ? prev.spaced : undefined)) {
+      } else if (__indexOf.call(LOGIC, value) >= 0 || value === '?' && (prev != null ? prev.spaced : void 0)) {
         tag = 'LOGIC';
       } else if (prev && !prev.spaced) {
         if (value === '(' && (_ref4 = prev[0], __indexOf.call(CALLABLE, _ref4) >= 0)) {
@@ -565,7 +565,7 @@
     return Lexer;
   })();
   JS_KEYWORDS = ['true', 'false', 'null', 'this', 'new', 'delete', 'typeof', 'in', 'instanceof', 'return', 'throw', 'break', 'continue', 'debugger', 'if', 'else', 'switch', 'for', 'while', 'try', 'catch', 'finally', 'class', 'extends', 'super'];
-  COFFEE_KEYWORDS = ['then', 'unless', 'until', 'loop', 'of', 'by', 'when'];
+  COFFEE_KEYWORDS = ['undefined', 'then', 'unless', 'until', 'loop', 'of', 'by', 'when'];
   for (op in COFFEE_ALIASES = {
     and: '&&',
     or: '||',
@@ -608,7 +608,7 @@
   COMPARE = ['==', '!=', '<', '>', '<=', '>='];
   MATH = ['*', '/', '%'];
   RELATION = ['IN', 'OF', 'INSTANCEOF'];
-  BOOL = ['TRUE', 'FALSE', 'NULL'];
+  BOOL = ['TRUE', 'FALSE', 'NULL', 'UNDEFINED'];
   NOT_REGEX = ['NUMBER', 'REGEX', 'BOOL', '++', '--', ']'];
   CALLABLE = ['IDENTIFIER', 'STRING', 'REGEX', ')', ']', '}', '?', '::', '@', 'THIS', 'SUPER'];
   INDEXABLE = CALLABLE.concat('NUMBER', 'BOOL');
diff --git a/lib/nodes.js b/lib/nodes.js
index 16119bdf..a4919e63 100644
--- a/lib/nodes.js
+++ b/lib/nodes.js
@@ -76,7 +76,7 @@
       contains = false;
       this.traverseChildren(false, function(node, arg) {
         var rearg;
-        return (rearg = block(node, arg)) === true ? !(contains = true) : arg != null ? rearg : undefined;
+        return (rearg = block(node, arg)) === true ? !(contains = true) : arg != null ? rearg : void 0;
       }, arg);
       return contains;
     };
@@ -311,7 +311,7 @@
     Return.prototype.makeReturn = THIS;
     Return.prototype.compile = function(o, level) {
       var _ref2, expr;
-      expr = (_ref2 = this.expression) != null ? _ref2.makeReturn() : undefined;
+      expr = (_ref2 = this.expression) != null ? _ref2.makeReturn() : void 0;
       return expr && !(expr instanceof Return) ? expr.compile(o, level) : Return.__super__.compile.call(this, o, level);
     };
     Return.prototype.compileNode = function(o) {
@@ -384,7 +384,7 @@
     Value.prototype.cacheReference = function(o) {
       var base, bref, name, nref;
       name = last(this.properties);
-      if (this.properties.length < 2 && !this.base.isComplex() && !(name != null ? name.isComplex() : undefined)) {
+      if (this.properties.length < 2 && !this.base.isComplex() && !(name != null ? name.isComplex() : void 0)) {
         return [this, this];
       }
       base = new Value(this.base, this.properties.slice(0, -1));
@@ -1029,7 +1029,7 @@
       empty = this.body.expressions.length === 0;
       delete o.bare;
       delete o.globals;
-      splat = undefined;
+      splat = void 0;
       params = [];
       _ref2 = this.params;
       for (i = 0, _len = _ref2.length; i < _len; i++) {
@@ -1091,7 +1091,7 @@
       return this.tags.front ? "(" + func + ")" : func;
     };
     Code.prototype.traverseChildren = function(crossScope, func) {
-      return crossScope ? Code.__super__.traverseChildren.call(this, crossScope, func) : undefined;
+      return crossScope ? Code.__super__.traverseChildren.call(this, crossScope, func) : void 0;
     };
     return Code;
   })();
@@ -1152,7 +1152,7 @@
         o.scope.assign(len, 'arguments.length');
         variadic = o.scope.freeVariable('result');
         o.scope.assign(variadic, len + ' >= ' + this.arglength);
-        end = this.trailings.length ? ", " + len + " - " + this.trailings.length : undefined;
+        end = this.trailings.length ? ", " + len + " - " + this.trailings.length : void 0;
         _ref2 = this.trailings;
         for (idx = 0, _len = _ref2.length; idx < _len; idx++) {
           trailing = _ref2[idx];
@@ -1201,8 +1201,8 @@
     While = (function() {
       function While(condition, opts) {
         While.__super__.constructor.call(this);
-        this.condition = (opts != null ? opts.invert : undefined) ? condition.invert() : condition;
-        this.guard = opts != null ? opts.guard : undefined;
+        this.condition = (opts != null ? opts.invert : void 0) ? condition.invert() : condition;
+        this.guard = opts != null ? opts.guard : void 0;
         return this;
       }
       return While;
@@ -1428,7 +1428,7 @@
       var catchPart, errorPart;
       o.indent = this.idt(1);
       errorPart = this.error ? " (" + (this.error.compile(o)) + ") " : ' ';
-      catchPart = this.recovery ? " catch" + errorPart + "{\n" + (this.recovery.compile(o, LEVEL_TOP)) + "\n" + this.tab + "}" : !(this.ensure || this.recovery) ? ' catch (_e) {}' : undefined;
+      catchPart = this.recovery ? " catch" + errorPart + "{\n" + (this.recovery.compile(o, LEVEL_TOP)) + "\n" + this.tab + "}" : !(this.ensure || this.recovery) ? ' catch (_e) {}' : void 0;
       return ("" + this.tab + "try {\n" + (this.attempt.compile(o, LEVEL_TOP)) + "\n" + this.tab + "}" + (catchPart || '')) + (this.ensure ? " finally {\n" + (this.ensure.compile(o, LEVEL_TOP)) + "\n" + this.tab + "}" : '');
     };
     return Try;
@@ -1540,8 +1540,8 @@
     For.prototype.compileNode = function(o) {
       var _ref2, _ref3, _ref4, _ref5, _ref6, body, code, cond, defPart, forPart, guardPart, idt, index, ivar, lvar, name, namePart, pvar, retPart, rvar, scope, sourcePart, step, svar, tail, tvar, varPart, vars;
       scope = o.scope;
-      name = !this.pattern && ((_ref2 = this.name) != null ? _ref2.compile(o) : undefined);
-      index = (_ref3 = this.index) != null ? _ref3.compile(o) : undefined;
+      name = !this.pattern && ((_ref2 = this.name) != null ? _ref2.compile(o) : void 0);
+      index = (_ref3 = this.index) != null ? _ref3.compile(o) : void 0;
       ivar = !index ? scope.freeVariable('i') : index;
       varPart = guardPart = defPart = retPart = '';
       body = Expressions.wrap([this.body]);
@@ -1572,7 +1572,7 @@
         } else {
           sourcePart = svar = this.source.compile(o, LEVEL_PAREN);
         }
-        namePart = this.pattern ? new Assign(this.name, new Literal("" + svar + "[" + ivar + "]")).compile(o, LEVEL_TOP) : name ? "" + name + " = " + svar + "[" + ivar + "]" : undefined;
+        namePart = this.pattern ? new Assign(this.name, new Literal("" + svar + "[" + ivar + "]")).compile(o, LEVEL_TOP) : name ? "" + name + " = " + svar + "[" + ivar + "]" : void 0;
         if (!this.object) {
           if (0 > pvar && (pvar | 0) === +pvar) {
             vars = "" + ivar + " = " + svar + ".length - 1";
@@ -1659,7 +1659,7 @@
       var _i, _j, _len, _len2, _ref2, _ref3, _ref4, _ref5, block, body, code, cond, conditions, expr, i, idt1, idt2;
       idt1 = this.idt(1);
       idt2 = o.indent = this.idt(2);
-      code = this.tab + ("switch (" + (((_ref2 = this.subject) != null ? _ref2.compile(o, LEVEL_PAREN) : undefined) || false) + ") {\n");
+      code = this.tab + ("switch (" + (((_ref2 = this.subject) != null ? _ref2.compile(o, LEVEL_PAREN) : void 0) || false) + ") {\n");
       for (i = 0, _len = this.cases.length; i < _len; i++) {
         _ref3 = this.cases[i], conditions = _ref3[0], block = _ref3[1];
         _ref4 = flatten([conditions]);
@@ -1711,11 +1711,11 @@
     If.prototype.children = ['condition', 'body', 'elseBody'];
     If.prototype.bodyNode = function() {
       var _ref2;
-      return (_ref2 = this.body) != null ? _ref2.unwrap() : undefined;
+      return (_ref2 = this.body) != null ? _ref2.unwrap() : void 0;
     };
     If.prototype.elseBodyNode = function() {
       var _ref2;
-      return (_ref2 = this.elseBody) != null ? _ref2.unwrap() : undefined;
+      return (_ref2 = this.elseBody) != null ? _ref2.unwrap() : void 0;
     };
     If.prototype.addElse = function(elseBody) {
       if (this.isChain) {
@@ -1728,7 +1728,7 @@
     };
     If.prototype.isStatement = function(o) {
       var _ref2;
-      return (o != null ? o.level : undefined) === LEVEL_TOP || this.bodyNode().isStatement(o) || ((_ref2 = this.elseBodyNode()) != null ? _ref2.isStatement(o) : undefined);
+      return (o != null ? o.level : void 0) === LEVEL_TOP || this.bodyNode().isStatement(o) || ((_ref2 = this.elseBodyNode()) != null ? _ref2.isStatement(o) : void 0);
     };
     If.prototype.compileNode = function(o) {
       return this.isStatement(o) ? this.compileStatement(o) : this.compileExpression(o);
@@ -1767,8 +1767,11 @@
       })) : "{\n" + (this.elseBody.compile(o, LEVEL_TOP)) + "\n" + this.tab + "}");
     };
     If.prototype.compileExpression = function(o) {
-      var _ref2, code;
-      code = this.condition.compile(o, LEVEL_COND) + ' ? ' + this.bodyNode().compile(o, LEVEL_LIST) + ' : ' + ((_ref2 = this.elseBodyNode()) != null ? _ref2.compile(o, LEVEL_LIST) : undefined);
+      var alt, body, code, cond;
+      cond = this.condition.compile(o, LEVEL_COND);
+      body = this.bodyNode().compile(o, LEVEL_LIST);
+      alt = this.elseBodyNode() ? this.elseBodyNode().compile(o, LEVEL_LIST) : 'void 0';
+      code = "" + cond + " ? " + body + " : " + alt;
       return o.level >= LEVEL_COND ? "(" + code + ")" : code;
     };
     If.prototype.unfoldSoak = function() {
diff --git a/lib/parser.js b/lib/parser.js
index 47bbc0dc..a2e53bc8 100755
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -81,7 +81,7 @@ case 35:this.$ = new yy.Literal($$[$0-1+1-1]);
 break;
 case 36:this.$ = new yy.Literal($$[$0-1+1-1]);
 break;
-case 37:this.$ = new yy.Literal($$[$0-1+1-1]);
+case 37:this.$ = new yy.Literal($$[$0-1+1-1] === 'undefined' ? 'void 0' : $$[$0-1+1-1]);
 break;
 case 38:this.$ = new yy.Assign($$[$0-3+1-1], $$[$0-3+3-1]);
 break;
diff --git a/lib/repl.js b/lib/repl.js
index 0f650143..1e57bb53 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -17,7 +17,7 @@
         globals: true,
         fileName: 'repl'
       });
-      if (val !== undefined) {
+      if (val !== void 0) {
         console.log(val);
       }
     } catch (err) {
diff --git a/lib/rewriter.js b/lib/rewriter.js
index b40065ff..e19ebcdc 100644
--- a/lib/rewriter.js
+++ b/lib/rewriter.js
@@ -63,15 +63,15 @@
         return 1;
       }
       before = tokens[i - 2], prev = tokens[i - 1], post = tokens[i + 1], after = tokens[i + 2];
-      if ((after != null ? after[0] : undefined) === 'INDENT') {
+      if ((after != null ? after[0] : void 0) === 'INDENT') {
         tokens.splice(i + 2, 1);
-        if ((before != null ? before[0] : undefined) === 'OUTDENT' && (post != null ? post[0] : undefined) === 'TERMINATOR') {
+        if ((before != null ? before[0] : void 0) === 'OUTDENT' && (post != null ? post[0] : void 0) === 'TERMINATOR') {
           tokens.splice(i - 2, 1);
         } else {
           tokens.splice(i, 0, after);
         }
       } else if (prev && ((_ref = prev[0]) !== 'TERMINATOR' && _ref !== 'INDENT' && _ref !== 'OUTDENT')) {
-        if ((post != null ? post[0] : undefined) === 'TERMINATOR' && (after != null ? after[0] : undefined) === 'OUTDENT') {
+        if ((post != null ? post[0] : void 0) === 'TERMINATOR' && (after != null ? after[0] : void 0) === 'OUTDENT') {
           tokens.splice.apply(tokens, [i + 2, 0].concat(tokens.splice(i, 2)));
           if (tokens[i + 2][0] !== 'TERMINATOR') {
             tokens.splice(i + 2, 0, ['TERMINATOR', '\n', prev[2]]);
@@ -92,7 +92,7 @@
         break;
       }
     }
-    return i ? this.tokens.splice(0, i) : undefined;
+    return i ? this.tokens.splice(0, i) : void 0;
   };
   exports.Rewriter.prototype.removeMidExpressionNewlines = function() {
     return this.scanTokens(function(token, i, tokens) {
@@ -147,7 +147,7 @@
       }
       _ref = this.tokens, one = _ref[i + 1], two = _ref[i + 2], three = _ref[i + 3];
       tag = token[0];
-      return (tag === 'TERMINATOR' || tag === 'OUTDENT') && !((two != null ? two[0] : undefined) === ':' || (one != null ? one[0] : undefined) === '@' && (three != null ? three[0] : undefined) === ':' || (one != null ? one[0] : undefined) === '(') || tag === ',' && one && ((_ref2 = one[0]) !== 'IDENTIFIER' && _ref2 !== 'NUMBER' && _ref2 !== 'STRING' && _ref2 !== '@' && _ref2 !== 'TERMINATOR' && _ref2 !== 'OUTDENT' && _ref2 !== '(');
+      return (tag === 'TERMINATOR' || tag === 'OUTDENT') && !((two != null ? two[0] : void 0) === ':' || (one != null ? one[0] : void 0) === '@' && (three != null ? three[0] : void 0) === ':' || (one != null ? one[0] : void 0) === '(') || tag === ',' && one && ((_ref2 = one[0]) !== 'IDENTIFIER' && _ref2 !== 'NUMBER' && _ref2 !== 'STRING' && _ref2 !== '@' && _ref2 !== 'TERMINATOR' && _ref2 !== 'OUTDENT' && _ref2 !== '(');
     };
     action = function(token, i) {
       return this.tokens.splice(i, 0, ['}', '}', token[2]]);
@@ -162,7 +162,7 @@
         start = stack.pop();
         return 1;
       }
-      if (!(tag === ':' && ((ago2 = this.tag(i - 2)) === ':' || (ago1 = this.tag(i - 1)) === ')' && this.tag(start[1] - 1) === ':' || ((_ref2 = stack[stack.length - 1]) != null ? _ref2[0] : undefined) !== '{'))) {
+      if (!(tag === ':' && ((ago2 = this.tag(i - 2)) === ':' || (ago1 = this.tag(i - 1)) === ')' && this.tag(start[1] - 1) === ':' || ((_ref2 = stack[stack.length - 1]) != null ? _ref2[0] : void 0) !== '{'))) {
         return 1;
       }
       stack.push(['{']);
@@ -200,7 +200,7 @@
       if (prev && !prev.spaced && tag === '?') {
         token.call = true;
       }
-      if (!(callObject || (prev != null ? prev.spaced : undefined) && (prev.call || (_ref2 = prev[0], __indexOf.call(IMPLICIT_FUNC, _ref2) >= 0)) && (__indexOf.call(IMPLICIT_CALL, tag) >= 0 || !(token.spaced || token.newLine) && __indexOf.call(IMPLICIT_UNSPACED_CALL, tag) >= 0))) {
+      if (!(callObject || (prev != null ? prev.spaced : void 0) && (prev.call || (_ref2 = prev[0], __indexOf.call(IMPLICIT_FUNC, _ref2) >= 0)) && (__indexOf.call(IMPLICIT_CALL, tag) >= 0 || !(token.spaced || token.newLine) && __indexOf.call(IMPLICIT_UNSPACED_CALL, tag) >= 0))) {
         return 1;
       }
       tokens.splice(i, 0, ['CALL_START', '(', token[2]]);
@@ -277,7 +277,7 @@
       }
       original = token;
       this.detectEnd(i + 1, condition, function(token, i) {
-        return token[0] !== 'INDENT' ? original[0] = 'POST_' + original[0] : undefined;
+        return token[0] !== 'INDENT' ? original[0] = 'POST_' + original[0] : void 0;
       });
       return 1;
     });
@@ -363,7 +363,7 @@
   };
   exports.Rewriter.prototype.tag = function(i) {
     var _ref;
-    return (_ref = this.tokens[i]) != null ? _ref[0] : undefined;
+    return (_ref = this.tokens[i]) != null ? _ref[0] : void 0;
   };
   BALANCED_PAIRS = [['(', ')'], ['[', ']'], ['{', '}'], ['INDENT', 'OUTDENT'], ['CALL_START', 'CALL_END'], ['PARAM_START', 'PARAM_END'], ['INDEX_START', 'INDEX_END']];
   INVERSES = {};
diff --git a/lib/scope.js b/lib/scope.js
index 6be6a0e1..f2bb27a8 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -71,10 +71,10 @@
     Scope.prototype.check = function(name, options) {
       var _ref2, immediate;
       immediate = !!this.type(name);
-      if (immediate || (options != null ? options.immediate : undefined)) {
+      if (immediate || (options != null ? options.immediate : void 0)) {
         return immediate;
       }
-      return !!((_ref2 = this.parent) != null ? _ref2.check(name) : undefined);
+      return !!((_ref2 = this.parent) != null ? _ref2.check(name) : void 0);
     };
     Scope.prototype.temporary = function(name, index) {
       return name.length > 1 ? '_' + name + (index > 1 ? index : '') : '_' + (index + parseInt(name, 36)).toString(36).replace(/\d/g, 'a');
diff --git a/src/grammar.coffee b/src/grammar.coffee
index 2ca9d16a..574d94bb 100644
--- a/src/grammar.coffee
+++ b/src/grammar.coffee
@@ -131,7 +131,8 @@ grammar =
     o 'AlphaNumeric'
     o 'JS',                                     -> new Literal $1
     o 'REGEX',                                  -> new Literal $1
-    o 'BOOL',                                   -> new Literal $1
+    o 'BOOL',                                   ->
+      new Literal if $1 is 'undefined' then 'void 0' else $1
   ]
 
   # Assignment of a variable, property, or index to a value.
@@ -486,24 +487,20 @@ grammar =
   # if-related rules are broken up along these lines in order to avoid
   # ambiguity.
   IfBlock: [
-    o 'IF Expression Block',                    -> new If $2, $3
-    o 'UNLESS Expression Block',                -> new If $2, $3, invert: true
-    o 'IfBlock ELSE IF Expression Block',       -> $1.addElse new If $4, $5
-    o 'IfBlock ELSE Block',                     -> $1.addElse $3
+    o 'IF Expression Block',              -> new If $2, $3
+    o 'UNLESS Expression Block',          -> new If $2, $3, invert: true
+    o 'IfBlock ELSE IF Expression Block', -> $1.addElse new If $4, $5
+    o 'IfBlock ELSE Block',               -> $1.addElse $3
   ]
 
   # The full complement of *if* expressions, including postfix one-liner
   # *if* and *unless*.
   If: [
     o 'IfBlock'
-    o 'Statement  POST_IF Expression',     ->
-      new If $3, Expressions.wrap([$1]), statement: true
-    o 'Expression POST_IF Expression',     ->
-      new If $3, Expressions.wrap([$1]), statement: true
-    o 'Statement  POST_UNLESS Expression', ->
-      new If $3, Expressions.wrap([$1]), statement: true, invert: true
-    o 'Expression POST_UNLESS Expression', ->
-      new If $3, Expressions.wrap([$1]), statement: true, invert: true
+    o 'Statement  POST_IF Expression',     -> new If $3, Expressions.wrap([$1]), statement: true
+    o 'Expression POST_IF Expression',     -> new If $3, Expressions.wrap([$1]), statement: true
+    o 'Statement  POST_UNLESS Expression', -> new If $3, Expressions.wrap([$1]), statement: true, invert: true
+    o 'Expression POST_UNLESS Expression', -> new If $3, Expressions.wrap([$1]), statement: true, invert: true
   ]
 
   # Arithmetic and logical operators, working on one or more operands.
diff --git a/src/lexer.coffee b/src/lexer.coffee
index 2c75e04a..ab7a6e05 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -116,10 +116,10 @@ exports.Lexer = class Lexer
         @identifierError id
     unless forcedIdentifier
       id  = COFFEE_ALIASES[id] if COFFEE_ALIASES.hasOwnProperty id
-      tag = if id is '!'                       then 'UNARY'
-      else  if id in ['==', '!=']              then 'COMPARE'
-      else  if id in ['&&', '||']              then 'LOGIC'
-      else  if id in ['true', 'false', 'null'] then 'BOOL'
+      tag = if id is '!'                                    then 'UNARY'
+      else  if id in ['==', '!=']                           then 'COMPARE'
+      else  if id in ['&&', '||']                           then 'LOGIC'
+      else  if id in ['true', 'false', 'null', 'undefined'] then 'BOOL'
       else  tag
     @token tag, id
     @token ':', ':' if colon
@@ -497,7 +497,7 @@ JS_KEYWORDS = [
 ]
 
 # CoffeeScript-only keywords.
-COFFEE_KEYWORDS = ['then', 'unless', 'until', 'loop', 'of', 'by', 'when']
+COFFEE_KEYWORDS = ['undefined', 'then', 'unless', 'until', 'loop', 'of', 'by', 'when']
 COFFEE_KEYWORDS.push op for all op of COFFEE_ALIASES =
   and  : '&&'
   or   : '||'
@@ -599,7 +599,7 @@ MATH    = ['*', '/', '%']
 RELATION = ['IN', 'OF', 'INSTANCEOF']
 
 # Boolean tokens.
-BOOL = ['TRUE', 'FALSE', 'NULL']
+BOOL = ['TRUE', 'FALSE', 'NULL', 'UNDEFINED']
 
 # Tokens which a regular expression will never immediately follow, but which
 # a division operator might.
diff --git a/src/nodes.coffee b/src/nodes.coffee
index 3a625bb6..0ded8aa0 100644
--- a/src/nodes.coffee
+++ b/src/nodes.coffee
@@ -1453,9 +1453,10 @@ exports.If = class If extends Base
 
   # Compile the If as a conditional operator.
   compileExpression: (o) ->
-    code = @condition .compile(o, LEVEL_COND) + ' ? ' +
-           @bodyNode().compile(o, LEVEL_LIST) + ' : ' +
-           @elseBodyNode()?.compile o, LEVEL_LIST
+    cond = @condition.compile o, LEVEL_COND
+    body = @bodyNode().compile o, LEVEL_LIST
+    alt  = if @elseBodyNode() then @elseBodyNode().compile(o, LEVEL_LIST) else 'void 0'
+    code = "#{cond} ? #{body} : #{alt}"
     if o.level >= LEVEL_COND then "(#{code})" else code
 
   unfoldSoak: -> @soak and this