[antlr-interest] TYpe-checking and error reporting

[Adam Connelly]

The way that I like to do it is to define exception classes that inherit
from RecognitionException for my semantic errors, and remove the error
reporting from the parser completely.  If you look at the thread, "Better
Error Reporting in ANTLR" you can see how I think it should be done.  Ter's
also put a bug report about it here:
http://www.antlr.org:8888/browse/ANTLR-244.

Not saying it's the best way to do it, but it feels right to me.

Adam

2008/5/14 <siemsen at ucar.edu>:

> I agree - we need better documentation about how to report semantic errors
> in ANTLR.  The book covers how to deal with lexer and parser errors, but not
> semantic errors like the one you describe.  Such errors should follow the
> standard style, with a file name, line number and character number, so I use
> these methods to report them:
>
> public void errorMessage (TokenStream inp, String msg) {
> String introString = "";
> if (!currentInputFileName.equals("")) {
> int lineNbr = inp.LT(1).getLine();
> int charPosition = inp.LT(1).getCharPositionInLine();
> introString = currentInputFileName + "(" + lineNbr + ":" + charPosition +
> "): ";
> }
> System.err.println(introString + msg);
> }
>  public void dieWithMessage (TokenStream inp, String msg) {
> errorMessage(inp, msg);
>         System.exit(1);
> }
>
> which I call with, like,
>
> dieWithMessage(input, "class " + classNam + " undefined");
>
> This "works" but smells bad:
>
>     1. It needs a global "currentFileName", which changes when there are
> includstream.
>     2. The methods take a TokenStream to get the line number and character
> position.  From reading ANTLR-generated code, I figured out that "input" is
> the token stream.  Perhaps I should pass in the token itself (input.LT(1))
> instead of the whole stream.
>     3. It doesn't use exceptions, which seems wrong.
>     4. Related to #3, it calls System.exit(), which makes unit testing
> difficult.
>
> Hopefully, this code will provoke enough disgust in better minds that
> they'll post superior approaches :-)
>
> -- Pete
>
> On May 13, 2008, at 6:38 PM, Robin Hamilton-Pennell wrote:
>
> 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
>
>
>
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