/ 
PerlX-Perform-0.006
River stage zero No dependents
/ PerlX::Perform

NAME

PerlX::Perform - syntactic sugar for if (defined ...) { ... }

SYNOPSIS

my $foo = function_that_might_return_undef();
perform { say $_ } wherever $foo;

my $bar = function_that_might_return_undef();
wherever $bar, perform { say $_ };

DESCRIPTION

Executes some code if a given scalar is defined. Within the code block, the scalar is available as $_.

Note that there is no comma before wherever here:

my $foo = function_that_might_return_undef();
perform { say $_ } wherever $foo;

But there is one before perform here:

my $bar = function_that_might_return_undef();
wherever $bar, perform { say $_ };

Gory Details

The implementation is pure Perl. The closest it gets to trickery is that the two functions defined by this package use prototypes.

perform

perform is a function can be called in two ways:

  • with a single coderef argument

    In this case, perform returns a blessed version of that coderef; a so-called Manifesto object.

  • with a coderef argument followed by a scalar

    Generates the Manifesto object, and executes the Manifesto on the scalar, returning the result.

    Or rather, it has the effective result of doing the above. But it inlines the logic from PerlX::Perform::Manifesto.

wherever

wherever is a function can be called in three ways:

  • with a single scalar argument

    In this case, wherever passes through the argument unchanged.

  • with a scalar argument and a Manifesto

    In this case, wherever executes the Manifesto with the scalar argument.

  • with a scalar argument and a coderef

    In this case, wherever turns the coderef into a Manifesto and executes it with the scalar argument.

This means that it's possible to do this:

my $manifesto = perform { say $_ };
wherever $foo, $manifesto;
wherever $bar, $manifesto;

And indeed wherever does allow a little additional syntactic sugar by skipping over the string "perform" if it is used as the second parameter. Thus you can write:

my $manifesto = perform { say $_ };
wherever $foo, perform => $manifesto;
wherever $bar, perform => $manifesto;

But because PerlX::Perform::Manifesto passes through any already-blessed coderefs, this will work too:

my $manifesto = perform { say $_ };
wherever $foo, &perform($manifesto);
wherever $bar, &perform($manifesto);

Tail Calls

Both perform and wherever make extensive use of goto in order to conceal their usage on the call stack.

whenever

This is available as an alias for wherever, but is not exported by default. You need to request it like:

use PerlX::Perform qw/perform whenever/;

BUGS

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Perform.

SEE ALSO

http://www.modernperlbooks.com/mt/2012/02/a-practical-use-for-macros-in-perl.html.

Scalar::Andand.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2012 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.