YAP6 Operator: Junction Operators
Date : 01 07 2008 Category : Web
O'Reilly Network Articles and WeblogsAnother 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 guysThe 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, 9and 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() == 42the 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).
LINKS Section “The Wonderful World of Junctions” from Exegesis 06 Section “Junctive operators” from Synopsis 03
Synopsis S03, the official source The introduction of this series Official Perl 6 Documentation Perl 6 in your browser