Re: rtl metadata musings

[Andy Wingo <wingo@pobox.com>]

On Sat 11 May 2013 06:48, Mark H Weaver <mhw@netris.org> writes:

> I have only one comment for now, which regards arity information.  The
> required/optional/rest representation is not sufficiently general.  Not
> only is it unable to handle empty case-lambdas, but it's also unable to
> properly represent a case-lambda that can accept 1 or 3 arguments, but
> not 2.

I did think about this and I think I just didn't express myself well.  I
said:

      struct guile_arity {
        Elf_Addr pc;
        Elf_Off size;
        nreq; // encodings for these not determined yet
        nopt;
        flags; // has-keyword-args, has-rest, is-case-lambda
        Elf_Offset offset;
      }

    An entry describes how many required, optional, keyword, and rest
    arguments a function has.  The .guile.arities section is prefixed by a
    length indicating how many entries there are, then all the arity
    structures, sorted by pc.  Note that one arity may contain another!  In
    particular for case-lambda clauses you can have one arity for the whole
    function, then a number of other ones for the cases.

The case-lambda as a whole would get the is-case-lambda flag.  The
arities of the clauses would follow and have their [pc*, pc*+size*]
within the [pc, pc+size] of the case-lambda entry.

I don't know whether to use the nreq/nopt/flags of the "outer" arity for
any purpose or not.

Cheers,

Andy
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