Hmm, I'm undecided about this. I've had a look over Quantum::Superpositions now, and it's got a lot of cool stuff in it. However, I see my approach as mostly syntactic sugar to replace things like:

if ($param eq 'this' || $param eq 'that' 
    || $param eq 'the other') {
  ...
}
[download]

if ($param eq any('this', 'that', 'the other') {
  ...
}
[download]

Taking a hint from hardburn above, I did some benchmarks (below) and there is a significant runtime difference, between using my code and Quantum::Superpositions'.

One feature from Quantum::Superpositions that I think would be worth adding, is

$result = any(1,2,3) * 2;
if ($result == 4) {...}
[download]

Tanktalus asked above about if (all(@x) eq any(@y) {...}. I can see how useful that would be, but would have to experiment to find a way to implement it without getting as big as Q::S, while not making the code too ugly.

Would Junction::Simple be a more fitting name? (I'm very hesitant to claim a top-name space)

Benchmark timings...

$ /usr/bin/perl ./benchmark.pl 
all: numeric (few)
                          Rate Quantum-Superpositions               Ju
+nction
Quantum-Superpositions  1842/s                     --                 
+  -94%
Junction               30303/s                  1545%                 
+    --

all: numeric (lots)
                         Rate Quantum-Superpositions               Jun
+ction
Quantum-Superpositions 1364/s                     --                  
+ -44%
Junction               2433/s                    78%                  
+   --

all: string
                         Rate Quantum-Superpositions               Jun
+ction
Quantum-Superpositions 1689/s                     --                  
+ -79%
Junction               8000/s                   374%                  
+   --

any: numeric (few)
                          Rate Quantum-Superpositions               Ju
+nction
Quantum-Superpositions   747/s                     --                 
+  -97%
Junction               28571/s                  3725%                 
+    --

any: numeric (lots)
                         Rate Quantum-Superpositions               Jun
+ction
Quantum-Superpositions 37.9/s                     --                  
+ -97%
Junction               1429/s                  3672%                  
+   --

any: string
                         Rate Quantum-Superpositions               Jun
+ction
Quantum-Superpositions  317/s                     --                  
+ -95%
Junction               6422/s                  1928%                  
+   --
[download]

#!/usr/bin/perl
use strict;
use warnings;
use Junction qw/ xall xany /;
use Quantum::Superpositions qw/ all any /;
use Benchmark ':all';

print "all: numeric (few)\n";

cmpthese(30_000,{
  Junction => sub {
    1 if xall(1..5) == 2;
  },
  'Quantum-Superpositions' => sub {
    1 if all(1..5) == 2;
  },
});

print "\nall: numeric (lots)\n";

cmpthese(30_000,{
  Junction => sub {
    1 if xall(1..300) == 250;
  },
  'Quantum-Superpositions' => sub {
    1 if all(1..300) == 250;
  },
});

print "\nall: string\n";

cmpthese(10_000,{
  Junction => sub {
    1 if xall('a'..'z') eq 'z';
  },
  'Quantum-Superpositions' => sub {
    1 if all('a'..'z') eq 'z';
  },
});

print "\nany: numeric (few)\n";

cmpthese(30_000,{
  Junction => sub {
    1 if xany(1..5) == 2;
  },
  'Quantum-Superpositions' => sub {
    1 if any(1..5) == 2;
  },
});

print "\nany: numeric (lots)\n";

cmpthese(2_000,{
  Junction => sub {
    1 if xany(1..300) == 250;
  },
  'Quantum-Superpositions' => sub {
    1 if any(1..300) == 250;
  },
});

print "\nany: string\n";

cmpthese(7_000,{
  Junction => sub {
    1 if xany('a'..'z') eq 'z';
  },
  'Quantum-Superpositions' => sub {
    1 if any('a'..'z') eq 'z';
  },
});
[download]