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Algebraic data types: Difference between revisions
→{{header|Perl 6}}: random cleanup
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multi balance($col, $a, $x, $b) is default { [$col, $a, $x, $b] }
proto
multi ins( $x, [] ) { ['R', [], $x, []] }
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}
my ([$, $a, $y, $b]) := ins($x, $s);
['B', $a, $y, $b];
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It does, however, use the generic comparison operators <tt>before</tt> and <tt>after</tt>, so it should work on any ordered type.
<lang perl6>sub MAIN {
my $t = [];
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Output:
<pre>["B", ["B", ["R", ["B", [], 1, []], 2, ["B", [], 3, []]], 4, ["B", [], 5, []]], 6, ["B", ["B", [], 7, []], 8, ["B", [], 9, ["R", [], 10, []]]]]</pre>
After we get enums and non-class generic scopes sorted out, we hope to be able to write the proto signatures with better parametric types. It'll look more like this:
<lang perl6>role Tree[::A] {
enum Color <R B>;
proto balance (Color, Tree[A], A, Tree[A]) {*}
multi balance(B,[R,[R,$a,$x,$b],$y,$c],$z,$d) { [R,[B,$a,$x,$b],$y,[B,$c,$z,$d]] }
...
}</lang>
And we can, if fact, write that and get it to parse currently. It's just the ability to instantiate that role in a non-class scope that is missing.
=={{header|Prolog}}==
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