Another article of the series “Yet Another Perl 6 Operator”
Perl 6 introduces a new scalar data-type: the “junction”. A junction is a single scalar value that can act like two or more values at once.
example a value which acts like any(1,2,3) 1 or 2 or 3 all(@vals) all members of @vals at the same time one(<moe curly larry>) one of the three stooges none(@bad_guys) none of the listed bad guys
The operators '|', '&' and '^' are now junction constructors, providing a syntactical complement to the functional variants any, all, one and none.
$a | $b any($a, $b) $x & $y all($x, $y) $me ^ $you one($me, $you)
The particular feature that make junctions interesting is that they thread through operations, returning another junction representing the result:
(1|2|3) + 4; # 5|6|7 (1|2) + (3&4); # (4|5) & (5|6)
The last example illustrates how when two junctions are applied through an operator, the result is a junction representing the operator applied to each combination of values.
Also operations on junctions will short-circuit as soon as possible, which will make them effective in both syntax and performance terms. For instance,
if $dave == 1|4|9 {
say "I'm sorry, Dave, you're just a square.";
}
reads better (and probably more understandable/maintainable) than using
$dave == 1 || $dave == 4 || $dave == 9
# or
grep { $_ == $dave }, 1, 4, 9
and resumes as soon as the comparison is true. This is even more compelling when testing collections against other collections. Thus,
if all(@newvals) > any(@oldvals) {
say "These are all bigger than something already seens."
}
is much finer than an equivalent version with nested greps (which is very prone to error when first writing — at least for mere human programmers).
Junctions are specifically unordered. So if you say
foo() | bar() | baz() == 42
the functions calls may happen in any order or in parallel. They can short-circuit as soon as any of them return 42. That makes junctions as well as other Perl 6 features like hyper-operators purposely amenable to parallelization.
Note. Consequently, with this choice of semantics for '|', '&' and '^', bitwise operators in Perl 6 now have different spellings (eg. '+|', '~|', etc.) – which is material for another micro-article.
Next article is due tomorrow (Jan 8, 2008).
