adding steps to range comprehensions

lib/coffee_script/CoffeeScript.tmbundle/Syntaxes/CoffeeScript.tmLanguage

@@ -204,7 +204,7 @@
 		</dict>
 		<dict>
 			<key>match</key>
-			<string>\b(break|catch|continue|else|finally|for|if|return|switch|then|throw|try|unless|when|while)\b</string>
+			<string>\b(break|by|catch|continue|else|finally|for|if|return|switch|then|throw|try|unless|when|while)\b</string>
 			<key>name</key>
 			<string>keyword.control.coffee</string>
 		</dict>

lib/coffee_script/grammar.y

@@ -8,7 +8,7 @@ token IDENTIFIER PROPERTY_ACCESS
 token CODE PARAM NEW RETURN
 token TRY CATCH FINALLY THROW
 token BREAK CONTINUE
-token FOR IN WHILE
+token FOR IN BY WHILE
 token SWITCH WHEN
 token DELETE INSTANCEOF TYPEOF
 token SUPER EXTENDS
@@ -32,7 +32,7 @@ prechigh
   left     '.'
   right    INDENT
   left     OUTDENT
-  right    WHEN IN
+  right    WHEN IN BY
   right    THROW FOR WHILE NEW SUPER ELSE
   left     UNLESS EXTENDS IF
   left     ASSIGN '||=' '&&='
@@ -321,8 +321,8 @@ rule
   # Looks a little confusing, check nodes.rb for the arguments to ForNode.
   For:
     Expression FOR
-      ForVariables ForSource          { result = ForNode.new(val[0], val[3][0], val[2][0], val[3][1], val[2][1]) }
-  | FOR ForVariables ForSource Block  { result = ForNode.new(val[3], val[2][0], val[1][0], val[2][1], val[1][1]) }
+      ForVariables ForSource          { result = ForNode.new(val[0], val[3], val[2][0], val[2][1]) }
+  | FOR ForVariables ForSource Block  { result = ForNode.new(val[3], val[2], val[1][0], val[1][1]) }
   ;
 
   # An array comprehension has variables for the current element and index.
@@ -333,9 +333,11 @@ rule
 
   # The source of the array comprehension can optionally be filtered.
   ForSource:
-    IN Expression                     { result = [val[1]] }
-  | IN Expression
-    WHEN Expression                   { result = [val[1], val[3]] }
+    IN Expression                     { result = {:source => val[1]} }
+  | ForSource
+    WHEN Expression                   { result = val[0].merge(:filter => val[2]) }
+  | ForSource
+    BY Expression                     { result = val[0].merge(:step => val[2]) }
   ;
 
   # Switch/When blocks.

lib/coffee_script/lexer.rb

@@ -12,7 +12,7 @@ module CoffeeScript
                   "new", "return",
                   "try", "catch", "finally", "throw",
                   "break", "continue",
-                  "for", "in", "where", "while",
+                  "for", "in", "by", "where", "while",
                   "switch", "when",
                   "super", "extends",
                   "delete", "instanceof", "typeof"]

lib/coffee_script/nodes.rb

@@ -360,11 +360,12 @@ module CoffeeScript
       write("#{idt}#{@from_var} = #{from_val};\n#{idt}#{@to_var} = #{to_val};\n#{idt}")
     end
 
-    def compile(o, idx=nil)
+    def compile(o, idx=nil, step=nil)
       raise SyntaxError, "unexpected range literal" unless idx
       vars     = "#{idx}=#{@from_var}"
+      step     = step ? step.compile(o) : '1'
       compare  = "(#{@from_var} <= #{@to_var} ? #{idx} #{less_operator} #{@to_var} : #{idx} #{greater_operator} #{@to_var})"
-      incr     = "(#{@from_var} <= #{@to_var} ? #{idx} += 1 : #{idx} -= 1)"
+      incr     = "(#{@from_var} <= #{@to_var} ? #{idx} += #{step} : #{idx} -= #{step})"
       write("#{vars}; #{compare}; #{incr}")
     end
 
@@ -609,10 +610,13 @@ module CoffeeScript
     custom_return
     custom_assign
 
-    attr_reader :body, :source, :name, :filter, :index
+    attr_reader :body, :source, :name, :index, :filter, :step
 
-    def initialize(body, source, name, filter, index=nil)
-      @body, @source, @name, @filter, @index = body, source, name, filter, index
+    def initialize(body, source, name, index=nil)
+      @body, @name, @index = body, name, index
+      @source = source[:source]
+      @filter = source[:filter]
+      @step   = source[:step]
     end
 
     def line_ending
@@ -634,7 +638,7 @@ module CoffeeScript
         var_part, pre_cond, post_cond = '', '', ''
         index_var   = scope.free_variable
         source_part = @source.compile_variables(o)
-        for_part    = "#{index_var}=0, #{@source.compile(o, ivar)}, #{index_var}++"
+        for_part    = "#{index_var}=0, #{@source.compile(o, ivar, @step)}, #{index_var}++"
       else
         index_var   = nil
         body_dent   = o[:indent] + TAB + TAB

test/fixtures/execution/test_range_comprehension.coffee

@@ -12,4 +12,9 @@ j = 5
 result: for j in [j..(j+3)]
   j
 
-print(result.join(' ') is '5 6 7 8')
+print(result.join(' ') is '5 6 7 8')
+
+# With range comprehensions, you can loop in steps.
+results: x for x in [0..25] by 5
+
+print(results.join(' ') is '0 5 10 15 20 25')