This week the following question was posed (and not properly answered) on the Stratego/XT mailing list and came up independently in a discussion with Peter Mosses about the syntax of OCaml. I had seen the problem and a solution to it before. I think it was Martin Bravenboer who used it in the syntax of AspectJ; but I can't find the source.
x + if y then z + a
should be parsed to the following abstract syntax tree:
Plus(Var("x"), If(Var("y"), Plus(Var("z"), Var("a"))))
The problem is that this cannot be solved directly using ambiguous binary expressions and just priorities and associativity declarations in SDF. But that does not mean there is no solution.