Course of Raku / Functional, concurrent, reactive, and web programming / Concurrent programming / Junctions

Autothreading

When you pass a junction to something that expects a single value — a comparison, or an ordinary function — Raku quietly applies that operation to every value behind the junction and joins the results back into a junction. This is called autothreading.

For example, adding to a junction adds to each of its values:

my $j = 1 | 2 | 3;
say $j + 10; # any(11, 12, 13)

The + 10 was applied to 1, 2, and 3 separately, giving a new any junction any(11, 12, 13).

With a comparison, the joined result collapses to a single truth value according to the junction’s kind:

say so all(3, 7, 2) > 0;  # True  — every value is positive
say so all(3, -1, 2) > 0; # False — not all are positive
say so none(1, 2, 3) == 5; # True — none of them is 5

Autothreading is what makes junctions so concise: one comparison checks many values. Conceptually the checks are independent, so Raku is free to run them in parallel — which is why junctions sit naturally in the concurrency toolkit.

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