Currying with .assuming

Fix some of a routine's arguments to make a new, smaller routine.

.assuming curries a routine: it binds some arguments now and returns a new Callable that takes the rest. It's partial application without writing a wrapper closure.

Fixing an argument #

sub add($a, $b) { $a + $b }
my &add5 = &add.assuming(5);
say add5(10);

15

add5 is add with its first argument fixed at 5, so add5(10) is add(5, 10).

Currying into a pipeline #

Because the result is a plain Callable, a curried routine drops straight into map, grep, or a feed — a tidy way to specialise a general routine at the call site.

sub scale($factor, $x) { $factor * $x }
my &double = &scale.assuming(2);
say (1, 2, 3).map(&double);

(2 4 6)

Notes #

• .assuming works with named arguments too: &f.assuming(:verbose) fixes a named option while leaving the positionals open.
• The result is an ordinary Callable, so it composes anywhere a block or sub is expected — map, grep, feeds, etc.
• Currying pairs well with the Whatever star: * + 5 is a quick one-off curry, while .assuming curries an existing named routine.