Sub::Infix(3pm)

Usage

   use Sub::Infix;
   
   # Operator needs to be defined (or imported) at compile time.
   BEGIN { *plus = infix { $_[0] + $_[1] } };
   
   my $five = 2 |plus| 3;

Overview

Sub::Infix creates fake infix operators using overloading. It doesn't use source filters, or Devel::Declare, or any of that magic. (Though Devel::Declare isn't magic enough to define infix operators anyway; I know; I've tried.) It's pure Perl, has no non-core dependencies, and runs on Perl 5.6.

The price you pay for its simplicity is that you cannot define an operator that can be used like this:

   my $five = 2 plus 3;

Instead, the operator needs to be wrapped with real Perl operators in one of three ways:

   my $five = 2 |plus| 3;
   my $five = 2 /plus/ 3;
   my $five = 2 <<plus>> 3;

The advantage of this is that it gives you three different levels of operator precedence.

You can also call the function a slightly less weird way:

   my $five = plus->(2, 3);

How does it work?

"2 |plus| 3" is parsed by perl as: "2 | ( &plus() | 3 )".

&plus() returns an object that overloads the "|" operator; let's call that $obj.

The overloaded "$obj | 3" operation stashes 3 inside $obj noting that the number is the right operand, and returns $obj.

Then "2 | $obj" is evaluated, stashing 2 inside $obj as the left operand. At this point, the object notices that it has both operands, and calls the coderef from the definition of the operator, passing it both operands.

Copyright and licence

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.

Releases

6 releases since Debian 8 (Jessie); the text changed 3 times.