= Raku Logic =

`raku(1)` offers several logical flow constructs.

<<TableOfContents>>

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== 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` [[Raku/Operators#Boolean_Operators|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 [[Raku/Types#Arrays|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.



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CategoryRicottone