adding a 'loop' keyword to CoffeeScript. Takes an expression or a block. Runs it until you break or return out.

examples/beautiful_code/regular_expression_matcher.coffee

@@ -21,7 +21,7 @@ match_here: (regexp, text) ->
 
 # Search for a kleene star match at the beginning of the text.
 match_star: (c, regexp, text) ->
-  while true
+  loop
     return true if match_here(regexp, text)
     return false unless text and (text[0] is c or c is '.')
     text: text.slice(1)

examples/code.coffee

@@ -94,7 +94,7 @@ while demand > supply
 
 while supply > demand then buy()
 
-while true
+loop
   break if broken
   continue if continuing
 

examples/potion.coffee

@@ -14,8 +14,7 @@ print(add(2, 4))
 
 # loop: 'quaff' print.
 
-while true
-  print('quaff')
+loop print 'quaff'
 
 
 # ('cheese', 'bread', 'mayo') at (1) print

examples/underscore.coffee

@@ -346,7 +346,7 @@
     return [] if len <= 0
     range:    new Array len
     idx:      0
-    while true
+    loop
       return range if (if step > 0 then i - stop else stop - i) >= 0
       range[idx]: i
       idx++

lib/grammar.js

@@ -484,6 +484,15 @@
         return $2.add_body(Expressions.wrap([$1]));
       }), o("Expression WhileSource", function() {
         return $2.add_body(Expressions.wrap([$1]));
+      }), o("Loop", function() {
+        return $1;
+      })
+    ],
+    Loop: [
+      o("LOOP Block", function() {
+        return new WhileNode(new LiteralNode('true')).add_body($2);
+      }), o("LOOP Expression", function() {
+        return new WhileNode(new LiteralNode('true')).add_body(Expressions.wrap([$2]));
       })
     ],
     // Array, object, and range comprehensions, at the most generic level.
@@ -747,7 +756,7 @@
   //     2 + (3 * 4)
   // And not:
   //     (2 + 3) * 4
-  operators = [["left", '?'], ["nonassoc", 'UMINUS', 'UPLUS', '!', '!!', '~', '++', '--'], ["left", '*', '/', '%'], ["left", '+', '-'], ["left", '<<', '>>', '>>>'], ["left", '&', '|', '^'], ["left", '<=', '<', '>', '>='], ["right", 'DELETE', 'INSTANCEOF', 'TYPEOF'], ["left", '==', '!='], ["left", '&&', '||'], ["right", '-=', '+=', '/=', '*=', '%=', '||=', '&&=', '?='], ["left", '.'], ["right", 'INDENT'], ["left", 'OUTDENT'], ["right", 'WHEN', 'LEADING_WHEN', 'IN', 'OF', 'BY', 'THROW'], ["right", 'FOR', 'WHILE', 'UNTIL', 'NEW', 'SUPER', 'CLASS'], ["left", 'EXTENDS'], ["right", 'ASSIGN', 'RETURN'], ["right", '->', '=>', 'UNLESS', 'IF', 'ELSE']];
+  operators = [["left", '?'], ["nonassoc", 'UMINUS', 'UPLUS', '!', '!!', '~', '++', '--'], ["left", '*', '/', '%'], ["left", '+', '-'], ["left", '<<', '>>', '>>>'], ["left", '&', '|', '^'], ["left", '<=', '<', '>', '>='], ["right", 'DELETE', 'INSTANCEOF', 'TYPEOF'], ["left", '==', '!='], ["left", '&&', '||'], ["right", '-=', '+=', '/=', '*=', '%=', '||=', '&&=', '?='], ["left", '.'], ["right", 'INDENT'], ["left", 'OUTDENT'], ["right", 'WHEN', 'LEADING_WHEN', 'IN', 'OF', 'BY', 'THROW'], ["right", 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'NEW', 'SUPER', 'CLASS'], ["left", 'EXTENDS'], ["right", 'ASSIGN', 'RETURN'], ["right", '->', '=>', 'UNLESS', 'IF', 'ELSE']];
   // Wrapping Up
   // -----------
   // Finally, now what we have our **grammar** and our **operators**, we can create

lib/lexer.js

@@ -658,7 +658,7 @@
   // CoffeeScript-only keywords, which we're more relaxed about allowing. They can't
   // be used standalone, but you can reference them as an attached property.
   COFFEE_ALIASES = ["and", "or", "is", "isnt", "not"];
-  COFFEE_KEYWORDS = COFFEE_ALIASES.concat(["then", "unless", "until", "yes", "no", "on", "off", "of", "by", "where", "when"]);
+  COFFEE_KEYWORDS = COFFEE_ALIASES.concat(["then", "unless", "until", "loop", "yes", "no", "on", "off", "of", "by", "where", "when"]);
   // The list of keywords that are reserved by JavaScript, but not used, or are
   // used by CoffeeScript internally. We throw an error when these are encountered,
   // to avoid having a JavaScript error at runtime.

lib/rewriter.js

@@ -423,7 +423,7 @@
   // Tokens indicating that the implicit call must enclose a block of expressions.
   IMPLICIT_BLOCK = ['->', '=>', '{', '[', ','];
   // Tokens that always mark the end of an implicit call for single-liners.
-  IMPLICIT_END = ['IF', 'UNLESS', 'FOR', 'WHILE', 'UNTIL', 'TERMINATOR', 'INDENT'].concat(EXPRESSION_END);
+  IMPLICIT_END = ['IF', 'UNLESS', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'TERMINATOR', 'INDENT'].concat(EXPRESSION_END);
   // Single-line flavors of block expressions that have unclosed endings.
   // The grammar can't disambiguate them, so we insert the implicit indentation.
   SINGLE_LINERS = ['ELSE', "->", "=>", 'TRY', 'FINALLY', 'THEN'];

src/grammar.coffee

@@ -416,6 +416,12 @@ grammar: {
     o "WhileSource Block",                      -> $1.add_body $2
     o "Statement WhileSource",                  -> $2.add_body Expressions.wrap [$1]
     o "Expression WhileSource",                 -> $2.add_body Expressions.wrap [$1]
+    o "Loop",                                   -> $1
+  ]
+
+  Loop: [
+    o "LOOP Block",                             -> new WhileNode(new LiteralNode 'true').add_body $2
+    o "LOOP Expression",                        -> new WhileNode(new LiteralNode 'true').add_body Expressions.wrap [$2]
   ]
 
   # Array, object, and range comprehensions, at the most generic level.
@@ -596,7 +602,7 @@ operators: [
   ["right",     'INDENT']
   ["left",      'OUTDENT']
   ["right",     'WHEN', 'LEADING_WHEN', 'IN', 'OF', 'BY', 'THROW']
-  ["right",     'FOR', 'WHILE', 'UNTIL', 'NEW', 'SUPER', 'CLASS']
+  ["right",     'FOR', 'WHILE', 'UNTIL', 'LOOP', 'NEW', 'SUPER', 'CLASS']
   ["left",      'EXTENDS']
   ["right",     'ASSIGN', 'RETURN']
   ["right",     '->', '=>', 'UNLESS', 'IF', 'ELSE']

src/lexer.coffee

@@ -323,7 +323,7 @@ exports.Lexer: class Lexer
   tag_parameters: ->
     return if @tag() isnt ')'
     i: 0
-    while true
+    loop
       i: + 1
       tok: @prev i
       return if not tok
@@ -466,7 +466,7 @@ JS_KEYWORDS: [
 # be used standalone, but you can reference them as an attached property.
 COFFEE_ALIASES:  ["and", "or", "is", "isnt", "not"]
 COFFEE_KEYWORDS: COFFEE_ALIASES.concat [
-  "then", "unless", "until",
+  "then", "unless", "until", "loop",
   "yes", "no", "on", "off",
   "of", "by", "where", "when"
 ]

src/rewriter.coffee

@@ -43,7 +43,7 @@ exports.Rewriter: class Rewriter
   # our feet.
   scan_tokens: (block) ->
     i: 0
-    while true
+    loop
       break unless @tokens[i]
       move: block @tokens[i - 1], @tokens[i], @tokens[i + 1], i
       i: + move
@@ -162,7 +162,7 @@ exports.Rewriter: class Rewriter
       @tokens.splice i + 1, 0, indent
       idx: i + 1
       parens: 0
-      while true
+      loop
         idx: + 1
         tok: @tokens[idx]
         pre: @tokens[idx - 1]
@@ -286,7 +286,7 @@ IMPLICIT_CALL:  ['IDENTIFIER', 'NUMBER', 'STRING', 'JS', 'REGEX', 'NEW', 'PARAM_
 IMPLICIT_BLOCK: ['->', '=>', '{', '[', ',']
 
 # Tokens that always mark the end of an implicit call for single-liners.
-IMPLICIT_END:   ['IF', 'UNLESS', 'FOR', 'WHILE', 'UNTIL', 'TERMINATOR', 'INDENT'].concat EXPRESSION_END
+IMPLICIT_END:   ['IF', 'UNLESS', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'TERMINATOR', 'INDENT'].concat EXPRESSION_END
 
 # Single-line flavors of block expressions that have unclosed endings.
 # The grammar can't disambiguate them, so we insert the implicit indentation.

test/test_while.coffee

@@ -36,3 +36,14 @@ results: until value
   i += 1
 
 ok i is 6
+
+
+# And, the loop form of while.
+i: 5
+list: []
+loop
+  i: - 1
+  break if i is 0
+  list.push i * 2
+
+ok list.join(' ') is '8 6 4 2'