Re: Parser then Attribute Grammar for C++

dezakin@usa.net (Dez Akin) wrote
> What I'm interested in is if its possible to do the parsing of C++ in
> stages, making a regular grammar for the lexer, a LL(k) grammmer for
> the first parser, and an attribute grammar to decorate the resulting
> syntax tree, or if the semantic ambiguities in C++ actually prevent
> such a clean layering.


Off the top of my head the main issue will proably be that without
tracking introduction of type names you can't know whether a legal
identifier is a variable or a type, and possibly a template name.


For instance, is "foo<a,bar>(5)" to be treated as a constructor call
of the template instance "foo<a,b>", or as two statements "foo < a"
and "bar > 5" involving the variables a and bar? You need at the very
least to know whether "foo" is a type name or not to be able to
resolve the amiguity.


To parse C++ without knowing type names you'd have to delay a lot of
error checking and be flexible about what you accept, potentially
having to rewrite the parse tree for constructs where you can't find a
meaningful generic representation.


I'd think the more common way of handling C++ would be to recognize
the few constructs that can introduce type names, and let your lexer
access that information to explicitly mark a token as a type name if
it is.


Vidar

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