On Thursday, 12 September 2013 at 14:09:43 UTC, H. S. Teoh wrote:
This can be handled by using an intermediate grammar rule.
Reduce all
(...) into an intermediate type, say ArgList, so the reduction
happens something like this:
int foo () () {}
Type Ident ArgList ArgList ^
Then have the rule:
CompileTimeArgs ::= ArgList
RuntimeArgs ::= ArgList
TemplateDecl ::= Type Ident CompileTimeArgs RuntimeArgs '{' ...
FuncDecl ::= Type Ident RuntimeArgs '{' ...
So first, all (...) gets parsed to ArgList, but it's not yet
fixed
whether they are compile-time arguments or runtime arguments.
It's only
after you see the next '(' or '{' that you decide whether
ArgList should
reduce to CompileTimeArgs or RuntimeArgs.
ArgList itself, of course, will accept all possible parameters
(both
runtime and compile-time): types, expressions, symbols. Then
when you
reduce it to RuntimeArgs, you reject stuff that can't be
interpreted as
parameter declarations.
And then you got to backtrack the parsing instead of the lexing.
You just moved the problem around. You'll have to create some
temporary ast nodes that then will fix into what they really are.
