apfelmus
It's intentionally impossible. Frisby uses a dynamic programming approach that crucially depends on the fact that the grammar in question is context-free (actually something related, but the effect is the same). You're trying to parse a context-sensitive language.
Aha, thanks, that makes sense: I am glad that for once I wasn't missing the obvious after all. Presumably this restriction allows it to gain other benefits. I hadn't realised that the different implementations of Frisby and Parsec had such far-reaching consequences. (snip)
This not a correct Pascal program, nevertheless the parse succeeds just fine. The missing declaration for y will be detected when processing the abstract syntax tree further. The key point is that the shape of the abstract syntax tree doesn't depend on whether y is declared or not.
Mmmmm, indeed it was a missing-declaration sort of problem I had in mind. Thanks for the example. -- Mark