Course of Raku / Functional, concurrent, reactive, and web programming / Functional programming / Reduction

The reduce metaoperator

Wrap any infix operator in square brackets and it becomes a reduction: it is inserted between every element of a list, collapsing the list to one value.

say [+] 1, 2, 3, 4, 5; # 15
say [*] 1, 2, 3, 4, 5; # 120

[+] sums the list as if you had written 1 + 2 + 3 + 4 + 5; [*] multiplies it. The same works with any infix operator:

say [max] 4, 9, 2, 7; # 9
say [min] 4, 9, 2, 7; # 2
say [~] 'a', 'b', 'c'; # abc

[max] reduces with the max operator to find the largest element, and [~] reduces with the string-concatenation operator ~ to glue the pieces together.

The reduce metaoperator works on any list, including a range:

say [+] 1..100; # 5050

It is one of Raku’s most compact and expressive features: a whole loop’s worth of accumulation in a pair of brackets.

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