On Tuesday 23 February 2010 03:02:32 Eric Niebler wrote:
You were SO close. You want proto::functional::flatten here (the type of a function object), not proto::flatten (an ordinary function).
Bah! Foiled again! :)
how do I talk about the vararg<> part in a semantic action? CalculatorGrammar has a use of vararg but it uses fold<> to process it. I don't want to fold a sequence, I want to pass it to a transform.
Manjunath already answered this one. Proto expressions already are fusion sequences, and proto::_expr returns the current is, expression. You can use proto::functional::pop_front in a transform to pop off the first bit (the thing that matches X in your example) and pass the result to something that accepts fusion sequences.
I tried this, but the manual says _expr returns the unmodified expression. Is there some way to send this through a transform to get the transformed expressions? For example, for a call operator: Name(Item, Item, Item) I want to get a sequence of the objects returned by processing the Items. In my case I am creating IR symbols, so it would be a sequence of pointers. Each Item is a proto expression that is married to a transform that returns an IR symbol for it. Originally I was going to run a fold<> that returned a std::vector<> of pointers to IR symbols but that seems inefficient and messy. I think it would be better to simply take the transformed results as they are, if it's possible. I'm just learning Fusion and it's a bit confusing as to where the compile-time ends and the run-time starts. I think I probably want to use transform_view, but I'm not sure what kind of function object to give it. I've attached a rather complex testcase to show what I'm attempting to do. I don't claim it's bug-free because I haven't yet got it to compile. I'm sure there's a lot of work to do to fix it. I'm attaching it because it's difficult to describe this in English. :) A function object for transform_view<> should implement something like ConstructUnary/BinarySymbol but there's no way to know what expression nodes are in the sequence and thus which function object should be use (Unary or Binary). I know you're going to tell me something obvious that looks trivial in retrospect. :) The #if 0'd code is the way I'd like to specify the grammar (i.e. without the FunctionTypeWithArgs / FunctionTypeWithoutArgs separation but when I do that I get a compiler error about a reference to void. Probably because I'm sending a null sequence to ConstructBinarySymbol. Any improvements to be had here? BTW, what's the difference between proto::_ and proto::_expr, as pop_front(_) vs. pop_front(_expr)? From what I can tell the manual gives essentially the same short description for both. -Dave