sub fred { 
    ...
    unless( defined wantarray ) { ...void context }
    elsif( wantarray )          { ...list context }
    else                        { ...scalar context }
    }

##</code><code>##

fred();               # void
my $fred    = fred(); # scalar
my( $fred ) = fred(); # list (because of the parens)
my @fred    = fred;   # list
print fred();         # list, print is a list operator
print scalar fred();  # scalar