Raku Logic

raku(1) offers several logical flow constructs.

Contents

Raku Logic
1. If
2. Unless
3. With
4. Without
5. For
6. Loop
7. Given

If

if structures can be written in two ways.

if $a < 2 {
  say 'Hello, world!'
}

say 'Hello, world!' if $a < 2 ;

No matter the way it is written, the condition always evaluates first.

Fall-through conditions are specified with elsif and else clauses.

if $b = 0 {
  say 'zero'
} elsif $b < 0 {
  say 'negative'
} else {
  say 'positive'
}

As with any other boolean contexts, a condition can be inverted with either the ! or not operators.

Unless

The unless structure is simply a negated if structure. It cannot take an else or elsif clause.

unless 2 <= $a {
  say 'Hello, world!'
}

With

The with structure is like an if structure that branches based on whether a variable is declared.

my $b;
with $b {
  say 'This never happens'
}

$b = 1;
with $b {
  say '$b is set'
}

Without

A negated with structure.

my $b;
without $b {
  say '$b is unset'
}

$b = 1;
without $b {
  say 'This never happens'
}

For

To loop over the elements of an array, try:

my @a = 1,2,3;

for @a -> $b {
  say $b
}

Loop

A classic loop.

loop (my $i = 0; $i < 5; $i++) {
  say $i
}

Given

To check a value for one or more conditions and branch based on those results, try:

my $a = 0;

given $var {
    when 1..10 { say '$a is within [1,10]' }
    when Int { say '$a is an integer' }
    when 42  { say '$a is exactly 0' }
    default  { say "the fall-through case" }
}

After matching a condition, the given structure is exited immediately. To override this behavior and continue trying cases, use the proceed keyword.

given $var {
    when 1..10 { say '$a is within [1,10]'; proceed }
    when Int { say '$a is an integer'; proceed }
    when 42  { say '$a is exactly 0' }
    default  { say "the fall-through case" }
}

But be sure to not include proceed on the penultimate case unless the fall-through case is intended to always execute.

CategoryRicottone