fixes #286: support stepped loops

src/compiler.coffee

@@ -445,19 +445,25 @@ class exports.Compiler
  block = forceBlock body
  block.body.push stmt helpers.undef() unless block.body.length
 
+ increment =
+ if @step? and not ((@step.instanceof CS.Int) and @step.data is 1)
+ (x) -> new JS.AssignmentExpression '+=', x, step
+ else
+ (x) -> new JS.UpdateExpression '++', yes, x
+
  # optimise loops over static, integral ranges
  if (@target.instanceof CS.Range) and
  # TODO: extract this test to some "static, integral range" helper
  ((@target.left.instanceof CS.Int) or ((@target.left.instanceof CS.UnaryNegateOp) and @target.left.expression.instanceof CS.Int)) and
  ((@target.right.instanceof CS.Int) or ((@target.right.instanceof CS.UnaryNegateOp) and @target.right.expression.instanceof CS.Int))
- varDeclaration = new JS.AssignmentExpression '=', i, compile @target.left
- update = new JS.UpdateExpression '++', yes, i
+ varDeclaration = new JS.VariableDeclaration 'var', [new JS.VariableDeclarator i, compile @target.left]
+ update = increment i
  if @filter?
  block.body.unshift stmt new JS.IfStatement (new JS.UnaryExpression '!', filter), new JS.ContinueStatement
  if keyAssignee?
  k = genSym 'k'
- varDeclaration = new JS.SequenceExpression [(new JS.AssignmentExpression '=', k, new JS.Literal 0), varDeclaration]
- update = new JS.SequenceExpression [(new JS.UpdateExpression '++', yes, k), update]
+ varDeclaration.declarations.unshift new JS.VariableDeclarator k, new JS.Literal 0
+ update = new JS.SequenceExpression [(increment k), update]
  block.body.unshift stmt new JS.AssignmentExpression '=', keyAssignee, k
  if valAssignee?
  block.body.unshift stmt new JS.AssignmentExpression '=', valAssignee, i
@@ -478,7 +484,7 @@ class exports.Compiler
  block.body.unshift stmt assignment keyAssignee, i
  if valAssignee?
  block.body.unshift stmt assignment valAssignee, new JS.MemberExpression yes, e, i
- new JS.ForStatement varDeclaration, (new JS.BinaryExpression '<', i, length), (new JS.UpdateExpression '++', yes, i), block
+ new JS.ForStatement varDeclaration, (new JS.BinaryExpression '<', i, length), (increment i), block
  ]
  [CS.ForOf, ({keyAssignee, valAssignee, target, filter, body}) ->
  block = forceBlock body

test/comprehensions.coffee

@@ -34,3 +34,12 @@ suite 'Comprehensions', ->
  test 'comprehension over range with index', ->
  arrayEq [0..3], (k for v, k in [5..8])
  arrayEq [5..8], (v for v, k in [5..8])
+
+ test '#286: stepped loops', ->
+ list = [1..7]
+ arrayEq [1, 4, 7], (v for v in list by 3)
+ arrayEq [1, 4, 7], (v for v in [1..7] by 3)
+ arrayEq [0, 3, 6], (k for v, k in list by 3)
+ arrayEq [0, 3, 6], (k for v, k in [1..7] by 3)
+ arrayEq [0, 0, 0], (0 for in list by 3)
+ arrayEq [0, 0, 0], (0 for in [1..7] by 3)