Author image Dmitry Karasik

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
         keyword => 'provided',
         package => scalar(caller),
         code    => 'if',
     ;
 }

 sub unimport {
    # disable keyword again
    Keyword::Pluggable::undefine keyword => 'provided', package => scalar(caller);
 }

 '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 scope that's currently being compiled. The scope can be lexical, packaged, and global.

Functions

Keyword::Pluggable::define %options
keyword

The keyword is injected in the scope currently being compiled

code (string or coderef)

For every occurrence of the keyword, your coderef will be called and its result will be injected into perl's parse buffer, so perl will continue parsing as if its contents had been the real source code in the first place. First paramater to the eventual coderef will be all code textref following the keyword to be replaced, if examination and change is needed.

expression

Boolean flag; if true then the perl parser will treat new code as expression, otherwise as a statement

global

Boolean flag; if set, then the scope is global, otherwise it is lexical or packaged

package

If set, the scope will be limited to that package, otherwise it will be lexical

Keyword::Pluggable::undefine %options

Allows options: keyword, global, package (see above).

Disables the keyword in the given scope. 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 it can only occur at the beginning of a statement, not embedded in an expression. To be able to do that, use expression => 1 flag.

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.