In enum Bool§

See primary documentation in context for prefix so

multi prefix:<so>(Mu --> Bool:D)

Coerces its argument to Bool, has looser precedence than prefix:<?>.

In Mu§

See primary documentation in context for method so

method so()

Evaluates the item in Boolean context (and thus, for instance, collapses Junctions), and returns the result. It is the opposite of not, and equivalent to the ? operator.

One can use this method similarly to the English sentence: "If that is so, then do this thing". For instance,

my @args = <-a -e -b -v>;
my $verbose-selected = any(@args) eq '-v' | '-V';
if $verbose-selected.so {
    say "Verbose option detected in arguments";
} # OUTPUT: «Verbose option detected in arguments␤»

The $verbose-selected variable in this case contains a Junction, whose value is any(any(False, False), any(False, False), any(False, False), any(True, False)). That is actually a truish value; thus, negating it will yield False. The negation of that result will be True. so is performing all those operations under the hood.

In Operators§

See primary documentation in context for prefix so

multi prefix:<so>(Mu $x --> Bool:D)

Evaluates its argument in Boolean context (and thus collapses Junctions), and returns the result.