The Whatever star *

A lone * that builds a one-argument function, or stands for "the end" in an index.

A bare * is the Whatever star. In most expressions it curries into a WhateverCode — a compact one-argument function — and in a subscript it means "from the end". It's what makes * > 2 and [*-1] read so cleanly.

Currying into a function #

An expression containing * becomes a function of the *s. * * 2 is "multiply by two"; * + * is a two-argument adder.

my &double = * * 2;
say double(5);
say (* + *)(3, 4);

10
7

In a subscript — from the end #

Inside [ ], * stands for the number of elements, so *-1 is the last index.

say [10, 20, 30, 40][*-1];
say (1..10)[*-2];

40
9

As a predicate #

Because * > 2 is a function, it drops straight into grep, map, sort, and when.

say (1..5).grep(* > 2);

(3 4 5)

Notes #

• The currying is per-expression: each * becomes one parameter, bound left to right, so * - * called with (10, 3) is 7.
• Currying stops at a , or a statement boundary; to use * across a wider expression (like a whole ~~), parenthesise the part you want curried — ~~ (* > 2), not ~~ * > 2.
• A standalone * in list context is a different beast — Inf-like "whatever the callee wants" — e.g. 1, 2 ... * for an unbounded sequence.