RFC 298 (v1) Make subroutines' prototypes accessible from Perl

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=head1 TITLE

Make subroutines' prototypes accessible from Perl

=head1 VERSION

  Maintainer: Simon Cozens <simon@brecon.co.uk>
  Date: 25 Sep 2000
  Mailing List: perl6-language-subs@perl.org
  Number: 298
  Version: 1
  Status: Developing

=head1 ABSTRACT

Allow sub prototypes to be got and set by Perl at compile time.

=head1 DESCRIPTION

The motivation behind this RFC is to allow subroutine attributes to
define canned "prototype classes". As a very trivial example:

    use attributes::prototype 'a_and_b' => "($a,$b)"

    sub foo : a_and_b { 
        # $a and $b are here set to what we knew as $_[0] and $_[1]
    }

Now, yes, I am suggesting that there be a C<attributes::prototype>
pragma, but that's not the thrust of my RFC - the point is how you
implement it, and you have to do this by making the prototype available.

That's the motivation; the justification is slightly different, and it's
to increase the flexibility and the possibilities for introspection that
Perl 6's subroutines provide the user. More flexibility is always a good
thing.

=head1 IMPLEMENTATION

There are a number of ways that this can be done; I'd originally thought
that there should be Yet Another Special Variable, but it seems more
Perlish to change C<prototype> to be a function which returns
the prototype of a built-in (same as Perl 5) or, when passed a fully
qualified sub name, an lvaluable subroutine to get or set the prototype
of that sub. 

So C<attributes::prototype> can then be implemented something vaguely
like this: store "prototype class" declarations in a hash, say,
C<%PROTOS>; register the new attributes; when the attribute is
processed, set C<prototype($sub) = $PROTOS{$attr}>.

=head1 REFERENCES

RFC 57: Subroutine prototypes and parameters

• RFC 298 (v1) Make subroutines' prototypes accessible from Perl by Perl6 RFC Librarian