Re: Supporting multiple input syntaxes

On Thursday, August 13, 2020 at 5:22:51 PM UTC-5, Hans-Peter Diettrich wrote:
> Am 13.08.2020 um 00:20 schrieb luser droog:
> > I've got my project successfully parsing the circa-1975 C syntax
> > from that old manual. I'd like to add parsers for K&R1 and c90
> > syntaxes.
> >
> > How separate should these be? Should they be complete
> > separate grammars, or more piecewise selection?
>
> IMO this depends widely on the usage of the parser output (diagnostics,
> backend...). C90 is much stricter than K&R, requires more checks. Do you
> need extensive error diagnostics, or do you assume that all source code
> is free of errors?
>
>
> > https://github.com/luser-dr00g/pcomb/blob/master/pc9syn.c
>
> You seem to implement an LL(1) parser? My C98 Parser is LL(2), i.e. an
> LL(1) parser with one or two locations where more lookahead is required.
> Also identifiers are classified as typenames and others prior to their
> usage.
>


Yes, it's basically LL(1) with backtracking. There's one part of the
grammar I'm using that's left-recursive and I still need to work that
out.


> For real-world testing (recommended!) a preprocessor is required and a
> copy of the standard libraries of existing compiler(s).
>
> Your test_syntax() source misses "=" from the variable declarations
> (initializers). What about pointer syntax/semantics? If you add these
> (and other) syntax differences conditionally (version specific) to your
> code, which way would look better to you? Which way will be safer to
> maintain?
>


That's actually correct for the 1975 dialect: no '=' to initialize
variables. I think it's pretty ugly without it, but it could be
removed anyway for the AST.


>
> Nice code BTW :-)
>


Thanks! I think I need to sidetrack a bit and work up some primitives
for pattern matching and decomposition to make the backend easier.
I'll report back if/when it can do more tricks.

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