stepping_slice.diff

diff --git a/src/grammar.coffee b/src/grammar.coffee
index 0c98198..d77293f 100644
--- a/src/grammar.coffee
+++ b/src/grammar.coffee
@@ -306,6 +306,7 @@ grammar: {
   Slice: [
     o "INDEX_START Expression . . Expression INDEX_END", -> new RangeNode $2, $5
     o "INDEX_START Expression . . . Expression INDEX_END", -> new RangeNode $2, $6, true
+    o "[ Expression : Expression : Expression ]", -> new SteppingRangeNode $2, $4, $6
   ]
 
   # The array literal.
diff --git a/src/nodes.coffee b/src/nodes.coffee
index a277c41..2b7cad2 100644
--- a/src/nodes.coffee
+++ b/src/nodes.coffee
@@ -513,6 +513,45 @@ exports.RangeNode: class RangeNode extends BaseNode
     arr:  Expressions.wrap([new ForNode(body, {source: (new ValueNode(this))}, literal(name))])
     (new ParentheticalNode(new CallNode(new CodeNode([], arr)))).compile(o)
 
+#### SteppingRangeNode
+
+# A Python-like slice literal.
+exports.SteppingRangeNode: class SteppingRangeNode extends BaseNode
+  type: 'SteppingRange'
+
+  constructor: (start, end, step) ->
+    @children:  [@start: start, @end: end, @step: step]
+
+  # Compiles the range's source variables -- where it starts and where it ends.
+  # TODO: compile_variables: (o) ->
+  # TODO:   @tab: o.indent
+  # TODO:   [@from_var, @to_var]: [o.scope.free_variable(), o.scope.free_variable()]
+  # TODO:   [from, to]:           [@from.compile(o), @to.compile(o)]
+  # TODO:   "$@from_var = $from; $@to_var = $to;\n$@tab"
+
+  # When compiled normally, the range returns the contents of the *for loop*
+  # needed to iterate over the values in the range. Used by comprehensions.
+  # TODO: compile_node: (o) ->
+  # TODO:   return    @compile_array(o) unless o.index
+  # TODO:   idx:      del o, 'index'
+  # TODO:   step:     del o, 'step'
+  # TODO:   vars:     "$idx = $@from_var"
+  # TODO:   step:     if step then step.compile(o) else '1'
+  # TODO:   equals:   if @exclusive then '' else '='
+  # TODO:   intro:    "($@from_var <= $@to_var ? $idx"
+  # TODO:   compare:  "$intro <$equals $@to_var : $idx >$equals $@to_var)"
+  # TODO:   incr:     "$intro += $step : $idx -= $step)"
+  # TODO:   "$vars; $compare; $incr"
+
+  # When used as a value, expand the range into the equivalent array. In the
+  # future, the code this generates should probably be cleaned up by handwriting
+  # it instead of wrapping nodes.
+  # TODO: compile_array: (o) ->
+  # TODO:   name: o.scope.free_variable()
+  # TODO:   body: Expressions.wrap([literal(name)])
+  # TODO:   arr:  Expressions.wrap([new ForNode(body, {source: (new ValueNode(this))}, literal(name))])
+  # TODO:   (new ParentheticalNode(new CallNode(new CodeNode([], arr)))).compile(o)
+
 #### SliceNode
 
 # An array slice literal. Unlike JavaScript's `Array#slice`, the second parameter
@@ -525,12 +564,21 @@ exports.SliceNode: class SliceNode extends BaseNode
     @children: [@range: range]
     this
 
-  compile_node: (o) ->
+  compile_range: (o) ->
     from:       @range.from.compile(o)
     to:         @range.to.compile(o)
     plus_part:  if @range.exclusive then '' else ' + 1'
     ".slice($from, $to$plus_part)"
 
+  compile_stepping_range: (o) ->
+    "// Look ma !"
+
+  compile_node: (o) ->
+    if @range instanceof RangeNode
+      @compile_range o
+    else if @range instanceof SteppingRange
+      @compile_stepping_range o
+
 #### ObjectNode
 
 # An object literal, nothing fancy.