=head1 TITLE

Symbols, symbols everywhere

=head1 VERSION

  Maintainer: Paolo Molaro <lupus@debian.org>
  Date: 26 Sep 2000
  Mailing List: perl6-internals@perl.org
  Number: 326
  Version: 1
  Status: Developing

=head1 ABSTRACT

Perl should adopt scheme-like symbols, both at the language level
and at the internals level.

=head1 DESCRIPTION

Symbols can be useful in a variety of ways both at the language
level and as an implementation detail for efficiency reasons.

=head2 Symbols at the language level

A possible operator to create a symbol could be qs// for B<q>uote B<s>ymbol.
A one character operator could be useful as well, but since ^ is likely
to be taken by curried expressions, an alternative could be C<:>.

	$symbol = qs(methodname); # or ^methodname or :methodname
	$object->$symbol;

They can be also useful in XS modules to map constants more efficiently
than today's constant() function.

Characters following the one-char operator are limited to the usual
identifier characters. Probably, the same character used as operator
should be used in subroutines prototypes to allow for compile time
optimizations.

Only equal/non equal comparison operations should be allowed on symbols.

=head2 Symbols in the inplementation

Symbols are "interned" during compilation. From then on symbols are
actually treated like numbers, so comparisons are faster. They should be
used to hold package names, method names and so on. This way symbol tables
can be implemented as optimized integer hash tables instead of string hash 
tables (for packages with few methods a binary search could be also a win).
A symbol should be used anywhere a package name or method name is used now
at the API level (this applies to variable names, too).

=head1 IMPLEMENTATION

Should be trivial. A symbol scalar could be a read-only scalar with both
the string and integer properties set. Note that additional memory should
not be allocated for each copy of a symbol: once "interned" they are  never 
free'd: the vtable stuff can make this very simple.

=head1 REFERENCES

Your preferred scheme book.

GLib's GQuarks and Xlib's Atoms for implementations.