Keyword::Simple(3) define new keywords in pure Perl


package Some::Module;

use Keyword::Simple;

sub import {
# create keyword 'provided', expand it to 'if' at parse time
Keyword::Simple::define 'provided', sub {
my ($ref) = @_;
substr($$ref, 0, 0) = 'if'; # inject 'if' at beginning of parse buffer

sub unimport {
# lexically disable keyword again
Keyword::Simple::undefine 'provided';


Warning: This module is still new and experimental. The API may change in future versions. The code may be buggy.

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


Takes two arguments, the name of a keyword and a coderef. 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.

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.


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

Every new keyword is actually a complete statement 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.

There are barely any tests.


Lukas Mai, "<l.mai at>"


Copyright 2012, 2013 Lukas Mai.

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 for more information.