NAME

Keyword::Pluggable - define new keywords in pure Perl

SYNOPSIS

 package Some::Module;
 
 use Keyword::Pluggable;
 
 sub import {
     # create keyword 'provided', expand it to 'if' at parse time
     Keyword::Pluggable::define 'provided', sub {
         my ($ref) = @_;
         substr($$ref, 0, 0) = 'if';  # inject 'if' at beginning of parse buffer
     };
 }
 
 sub unimport {
     # lexically disable keyword again
     Keyword::Pluggable::undefine 'provided';
 }

 'ok'

DESCRIPTION

Warning: This module is still new and experimental. The API may change in future versions. The code may be buggy. Also, this module is a fork from Keyword::Simple, that somehow got stalled. If its author accepts pull requests, then it will probably be best to use it instead.

This module lets you implement new keywords in pure Perl. To do this, you need to write a module and call Keyword::Pluggable::define in your import method. Any keywords defined this way will be available in the lexical scope that's currently being compiled.

Functions

Keyword::Pluggable::define

Takes three arguments, the name of a keyword, a coderef, and a boolean flag if the result of the keyword handler is an expression. Injects the keyword in the lexical scope currently being compiled. For every occurrence of the keyword, your coderef will be called with one argument: A reference to a scalar holding the rest of the source code (following the keyword).

You can modify this scalar in any way you like and after your coderef returns, perl will continue parsing from that scalar as if its contents had been the real source code in the first place.

Keyword::Pluggable::undefine

Takes one argument, the name of a keyword. Disables that keyword in the lexical scope that's currently being compiled. You can call this from your unimport method to make the no Foo; syntax work.

BUGS AND LIMITATIONS

This module depends on the pluggable keyword API introduced in perl 5.12. parse_ functions were introduced in 5.14. Older versions of perl are not supported.

Every new keyword is actually a complete statement or an expression by itself. The parsing magic only happens afterwards. This means that e.g. the code in the "SYNOPSIS" actually does this:

  provided ($foo > 2) {
    ...
  }

  # expands to

  ; if
  ($foo > 2) {
    ...
  }

The ; represents a no-op statement, the if was injected by the Perl code, and the rest of the file is unchanged.

This also means your new keywords can only occur at the beginning of a statement, not embedded in an expression.

Keywords in the replacement part of a s//.../e substitution aren't handled correctly and break parsing.

There are barely any tests.

AUTHOR

Lukas Mai, <l.mai at web.de> Dmitry Karasik , <dmitry at karasik.eu.org

COPYRIGHT & LICENSE

Copyright (C) 2012, 2013 Lukas Mai. Copyright (C) 2018 Dmitry Karasik

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.