RFC 83 (v1) Make constants look like variables

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=head1 TITLE

Make constants look like variables

=head1 VERSION

  Maintainer: Jeremy Howard <[email protected]>
  Date: 10 August 2000
  Version: 1
  Mailing List: [email protected]
  Number: 83

=head1 ABSTRACT

This RFC proposes that the current constant.pm module removed, and
replaced with a syntax allowing any variable to be marked as constant.

=head1 DESCRIPTION

Currently, constants are created in Perl using the constant.pm module:

  use constant PI => 3.1415926;

which creates an inlined subroutine:

  sub PI () {3.1415926;}

This method of creating constants has three serious drawbacks:
 
=over 8

=item Can not be interpolated in strings

Whereas variables can be interpolated into strings (e.g. "PI is $Pi"),
subroutines can not be. This makes using constants inconvenient, since
string concatenation must be used.

=item Inconsistant syntax

The sudden appearance of barewords can be quite unsettling to new users.
After becoming told that 'arrays are @name, scalars are $name, ...', the
rule suddenly stops working just because the programmer wants the value to
stay constant.

=item Redundant warnings

In persistant Perl environments such as mod_perl, inlined subroutines
often created the redundant warning 'Constant subroutine PI redefined'.
This has been a frequent source of confusion amongst new mod_perl users.

=back

It is proposed that a new syntax for declaring constants be introduced:

  my constant $PI = 3.1415926;
  my constant @FIB = (1,1,2,3,5,8,13,21);
  my constant %ENG_ERRORS = (E_UNDEF=>'undefined', E_FAILED=>'failed');
  
Constants can be lexically or globally scoped (or any other new scoping
level yet to be defined).

=head1 IMPLEMENTATION

Constants should have the same behaviour as the do now. They should be
inlined, and constant expressions should be calculated at compile time.

=head1 REFERENCES

perldoc constant; perldoc perlsub (for constant subroutines)