Control flow

for / while / until / loop

Full

Iterate a list with for, condition-loop with while/until, C-style with loop.

Raku's loops cover three needs: walking a list (for), repeating while a condition holds (while/until), and the explicit three-part C-style loop (loop).

for — iterate a list #

for binds each element to a signature variable. Use -> to name it.

for 1..3 -> $i {
    say "i=$i";
}
say "sum ", [+] 1..10;

Output

i=1
i=2
i=3
sum 55

Take more than one at a time, or index with .kv:

for <a b c>.kv -> $i, $v {
    say "$i: $v";
}

Output

0: a
1: b
2: c

while / until #

while repeats as long as its condition is true; until is its negation.

my $i = 3;
while $i > 0 {
    say $i;
    $i--;
}

Output

3
2
1

loop — the C-style form #

loop (init; test; step) { } is the explicit three-part loop. A bare loop { } with no parts runs forever (use last to break).

loop (my $j = 0; $j < 3; $j++) {
    say $j;
}

Output

0
1
2

Notes #

Loop control: last breaks out, next skips to the next iteration, redo reruns the current one.
for aliases read-write by default when you use <-> $x, so you can modify array elements in place.
The postfix form say $_ for 1..3 is the idiomatic one-liner for simple iteration.