Pragmatic - Adds pragmata to Exporter
In module MyModule.pm:
package MyModule; require Pragmatic; @ISA = qw (Pragmatic); %PRAGMATA = (mypragma => sub {...});
In other files which wish to use MyModule:
use MyModule qw (-mypragma); # Execute pragma at import time use MyModule qw (-mypragma=1,2,3); # Pass pragma argument list
Pragmatic implements a default import method for processing pragmata before passing the rest of the import to Exporter.
import
Perl automatically calls the import method when processing a use statement for a module. Modules and use are documented in perlfunc and perlmod.
use
(Do not confuse Pragmatic with pragmatic modules, such as less, strict and the like. They are standalone pragmata, and are not associated with any other module.)
Using Pragmatic modules is very simple. To invoke any particular pragma for a given module, include it in the argument list to use preceded by a hyphen:
use MyModule qw (-mypragma);
Pragmatic::import will filter out these arguments, and pass the remainder of the argument list from the use statement to Exporter::import (actually, to Exporter::export_to_level so that Pragmatic is transparent).
Pragmatic::import
Exporter::import
Exporter::export_to_level
If you want to pass the pragma arguments, use syntax similar to that of the -M switch to perl (see perlrun):
use MyModule qw (-mypragma=abc,1,2,3);
If there are any warnings or fatal errors, they will appear to come from the use statement, not from Pragmatic::import.
Writing Pragmatic modules with Pragmatic is straight-forward. First, require Pragmatic (you could use it instead, but it exports nothing, so there is little to gain thereby). Declare a package global %PRAGMATA, the keys of which are the names of the pragmata and their corresponding values the code references to invoke. Like this:
require Pragmatic
%PRAGMATA
package MyPackage; require Pragmatic; use strict; use vars qw (%PRAGMATA); sub something_else { 1; } %PRAGMATA = (first => sub { print "@_: first\n"; }, second => sub { $SOME_GLOBAL = 1; }, third => \&something_else, fourth => 'name_of_sub');
When a pragma is given in a use statement, the leading hyphen is removed, and the code reference corresponding to that key in %PRAGMATA, or a subroutine with the value's name, is invoked with the name of the package as the first member of the argument list (this is the same as what happens with import). Additionally, any arguments given by the caller are included (see "Using Pragmatic Modules", above).
use MyModule; # no pragmas use MyModule qw (-abc); # invoke C<abc> use MyModule qw (-p1 -p2); # invoke C<p1>, then C<p2>
use MyModule qw (-abc=1,2,3); # invoke C<abc> with (1, 2, 3) use MyModule qw (-p1 -p2=here); # invoke C<p1>, then C<p2> # with (1, 2, 3)
(Please see Exporter for a further explanatation.)
use MyModule ( ); # no pragmas, no exports use MyModule qw (fun1 -abc fun2); # import C<fun1>, invoke C<abc>, # then import C<fun2> use MyModule qw (:set1 -abc=3); # import set C<set1>, invoke C<abc> # with (3)
%PRAGMATA = (debug => sub { $DEBUG = 1; });
my $fred = sub { 'fred'; }; my $barney = sub { 'barney'; }; %PRAGMATA = (fred => sub { local $^W = 0; *flintstone = $fred; }, barney => sub { local $^W = 0; *flintstone = $barney; });
%PRAGMATA = (super => sub { shift; push @ISA, @_; });
package X; @ISA = qw(Pragmatic); %PRAGMATA = (debug => 'debug'); $DEBUG = 0; sub debug { ${"$_[0]::DEBUG"} = 1; } package Y: @ISA = qw(X); %PRAGMATA = (debug => 'debug'); $DEBUG = 0;
Exporter
Exporter does all the heavy-lifting (and is a very interesting module to study) after Pragmatic has stripped out the pragmata from the use.
The following are the diagnostics generated by Pragmatic. Items marked "(W)" are non-fatal (invoke Carp::carp); those marked "(F)" are fatal (invoke Carp::croak).
Carp::carp
Carp::croak
(F) The caller tried something like "use MyModule (-xxx)" where there was no pragma xxx defined for MyModule.
(F) The writer of the called package tried something like "%PRAGMATA = (xxx => not_a_sub)" and either assigned xxx a non-code reference, or xxx is not a method in that package.
(W) The pramga returned a false value. The module is possibly in an inconsisten state after this. Proceed with caution.
B. K. Oxley (binkley) <binkley@alumni.rice.edu>
Copyright 1999-2005, B. K. Oxley.
This library is free software; you may redistribute it and/or modify it under the same terms as Perl itself.
Thanks to Kevin Caswick <KCaswick@wspackaging.com> for a great patch to run under Perl 5.8.
To install Pragmatic, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Pragmatic
CPAN shell
perl -MCPAN -e shell install Pragmatic
For more information on module installation, please visit the detailed CPAN module installation guide.