RFC 168 (v1) Built-in functions should be functions

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=head1 TITLE

Built-in functions should be functions

=head1 VERSION

  Maintainer: Johan Vromans <[email protected]>
  Date: 27 Aug 2000
  Mailing List: [email protected]
  Version: 1
  Number: 168

=head1 ABSTRACT

RFC 26 proposes to eliminate the distinction between functions and
operators from a language perspective.

This RFC proposes that all Perl built-in functions should be usable in
all ways normal functions can be used. It is part of a big consipracy
to remove the number of cases with exceptional behaviour in Perl.

=head1 DESCRIPTION

Named operators, like C<abs>, can be called like functions in which
case they behave like functions. However, that's where the similarity
ends. You cannot override most builtins, and cannot tack a reference
to them. 

There is no reason why the built-ins should be treated differently. A
famous Perl saying reads "if it looks like a function, it B<is> a
function." So be it.

In particular, it is desired that every built-in

=over 4

=item *

can be overridden by a user defined subroutine;

=item *

can have a reference taken;

=item *

has a useful prototype.

=back

=head2 Overriding

The principle of least surprise dictates that

    sub I<foo> { return 10 }
    print I<foo>();

should call I<foo>() and print "10" for all I<foo>.

Currently, most built-ins are excluded from this. For example:

    sub system { return 10 }
    print system();

Instead of calling the user defined system(), the built-in is used.

The second line may give a warning, but only if warnings are enabled:

    Ambiguous call resolved as CORE::system(), qualify as such or use &

=head2 References

You can call a built-in, but not take a reference.

    $a = \&system;
    print $a->(-1)

This gives an error:

    Undefined subroutine &main::system called

This should return a reference to the built-in instead.

Since C<&>I<foo> implicitly refers to the current package, it would be
acceptible to require

    $a = \&CORE::system;

Note that this currently (5.7.0 DEVEL6806) results in the error:

    Undefined subroutine &CORE::system called

which is surprising, if not misleading.

=head2 Prototypes

Currently, several built-ins do not provide prototype information. 

    prototype("CORE::abs")  ==>  ;$
    prototype("CORE::shift")  ==>  undef

This must be fixed. One might even call this a bug, although the
current prototype mechanism is not powerful enough to cope with all
built-ins. 

=head1 REFERENCES

RFC 26: Named operators versus functions

Tom Christiansen in <12231.967154045@chthon> (perl6-internals, Aug 24, 2000).