[antlr-interest] TYpe-checking and error reporting

[Robin Hamilton-Pennell]

Howdy all,

I've been using ANTLR for a little while now and it has been mostly
smooth sailing. For my target DSL I've successfully built a lexer,
parser which generates ASTs, and tree grammar to pretty-print the
ASTs. So, my app works great as nothing more than a pretty printer at
this point, but it's a step, at least.

I started implementing code to perform some basic static type
checking. I build symbol tables in the parser, and in the tree grammar
I am able to access the type information. This I got working as
expected.

I ran into a snag when attempting to do some error reporting. For the
purposes of this question, I'll show you a snippet of target code
(it's in a C-like syntax):

int foo;
int bar;
{
    int foo; // This is valid, as it's in a different scope than the foo above
}
int foo; // This is illegal, as the variable "foo" in the same scope
is being redeclared.

I have a method, boolean isDefined(String identifier), which works as
expected to catch this error (for example, if I embed a
System.err.println() action). However, I cannot figure out the best
approach to report the error!

I've perused the book and website to find a solution, and searched the
mailing list briefly, to no avail. I can use semantic predicates, but
the resulting error messages are next-to-useless. Has anyone tackled
this problem before, and if so, what's the recommended path for
reporting semantic errors (without sem preds, if possible)? I really
appreciate any help that can be provided.

Thanks!
Robin