Fixes #284 - Loops/comprehensions over decreasing ranges don't work (#…

…365)

* Fixes #284 - Loops/comprehensions over decreasing ranges don't work

* - Fix code formatting
- Add more unit tests for decreasing numeric ranges

src/compiler.coffee

@@ -316,6 +316,21 @@ generateSoak = do ->
  [tests, e] = fn node
  new CS.Conditional (foldl1 tests, (memo, t) -> new CS.LogicalAndOp memo, t), e
 
+extractNumber = (what) ->
+ return what.data if what.instanceof CS.Int
+ return false unless what.instanceof CS.UnaryNegateOp
+ return false unless what.expression.instanceof CS.Int
+ return 0 - what.expression.data
+
+extractStaticRange = (range) ->
+ return undefined unless range.instanceof CS.Range
+ left = extractNumber range.left
+ right = extractNumber range.right
+
+ return undefined if left == false
+ return undefined if right == false
+
+ return [left, right]
 
 helperNames = {}
 helpers =
@@ -392,7 +407,6 @@ for own h, fn of inlineHelpers
  helpers[h] = fn
 
 
-
 class exports.Compiler
 
  @compile = => (new this).compile arguments...
@@ -449,17 +463,17 @@ class exports.Compiler
  block = forceBlock body
  block.body.push stmt helpers.undef() unless block.body.length
 
+ numericRange = extractStaticRange(@target)
  increment =
  if @step? and not ((@step.instanceof CS.Int) and @step.data is 1)
  (x) -> new JS.AssignmentExpression '+=', x, step
+ else if numericRange? and numericRange[1] < numericRange[0]
+ (x) -> new JS.UpdateExpression '--', yes, x
  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))
+ if numericRange?
  varDeclaration = new JS.VariableDeclaration 'var', [new JS.VariableDeclarator i, compile @target.left]
  update = increment i
  if @filter?
@@ -471,7 +485,10 @@ class exports.Compiler
  block.body.unshift stmt new JS.AssignmentExpression '=', keyAssignee, k
  if valAssignee?
  block.body.unshift stmt new JS.AssignmentExpression '=', valAssignee, i
- op = if @target.isInclusive then '<=' else '<'
+ if numericRange[1] > numericRange[0]
+ op = if @target.isInclusive then '<=' else '<'
+ else
+ op = if @target.isInclusive then '>=' else '>'
  return new JS.ForStatement varDeclaration, (new JS.BinaryExpression op, i, compile @target.right), update, block
 
  e = if needsCaching @target then genSym 'cache' else target

test/comprehensions.coffee

@@ -43,3 +43,17 @@ suite 'Comprehensions', ->
  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)
+
+ test '#284: loops/comprehensions over decreasing ranges don\'t work', ->
+ a = 2
+ b = -2
+ arrayEq [5, 4, 3, 2, 1], (n for n in [5..1])
+ arrayEq [5, 4, 3, 2, 1, 0, -1, -2, -3, -4, -5], (n for n in [5..-5])
+ arrayEq [2, 1, 0, -1, -2], (n for n in [a..b])
+ arrayEq [2, 1, 0, -1, -2], (n for n in [a..-2])
+ arrayEq [2, 1, 0, -1, -2], (n for n in [2..b])
+
+ arrayEq [5, 4, 3, 2], (n for n in [5...1])
+ arrayEq [2, 1, 0, -1], (n for n in [a...b])
+ arrayEq [2, 1, 0, -1], (n for n in [a...-2])
+ arrayEq [2, 1, 0, -1], (n for n in [2...b])