inconsistent parsing of curly surface syntax with keywords/parameters

[mlubin]

The expression tree generated for keyword arguments changes if parameters are present or not:

julia> dump(:(f{a=1}))
Expr 
  head: Symbol curly
  args: Array(Any,(2,))
    1: Symbol f
    2: Expr 
      head: Symbol =
      args: Array(Any,(2,))
        1: Symbol a
        2: Int64 1
      typ: Any
  typ: Any

julia> dump(:(f{a=1;b=2}))
Expr 
  head: Symbol curly
  args: Array(Any,(3,))
    1: Symbol f
    2: Expr 
      head: Symbol keywords
      args: Array(Any,(1,))
        1: Expr 
          head: Symbol =
          args: Array(Any,(2,))
          typ: Any
      typ: Any
    3: Expr 
      head: Symbol parameters
      args: Array(Any,(1,))
        1: Expr 
          head: Symbol =
          args: Array(Any,(2,))
          typ: Any
      typ: Any
  typ: Any

This makes it more difficult to parse inside macros. I'd actually prefer to not have the keyword arguments separate in this case, because it destroys the order and makes it impossible to parse the difference between f{1,y=2} and f{y=2,1} which is important for the syntax of MathProg, where it means something entirely different from keyword arguments.

[JeffBezanson]

Related: #3143

The big problem here is that in some cases, calls contain assignments that are not keyword arguments. For example you can write x = (y=z) + 2, which does an assignment instead of passing a keyword argument to +. I think the only way I can resolve this is to parse keyword arguments as (kw a b) instead of (= a b). Then you would have to know to look for :kw instead of :(=), but these other problems would not be there. Does that seem ok?

[mlubin]

MathProg's use of = was in part because the syntax was available, we use it for sum{ x[i]*y[i], i = 1:N }. I'd be happy to use in instead to avoid the conflicts with keyword arguments, if that syntax could be made parseable, i.e., sum{ x[i]*y[i], i in 1:N }. Otherwise, it's easy to look for :kw instead of :=, but it would be great if the order wasn't destroyed.

[mlubin]

Awesome