multi sub prefix:<foo> (Str $a) {
     return $a eq "foo" ?? "bar" !! "foo";
}

##</code><code>##

foo "foo";

##</code><code>##


BEGIN {
    eval 
    "
multi * prefix:<foo> (Str $a) is tighter(&infix:<~>) {
     return $a eq 'foo' ?? 'bar' !! 'foo';
    ";
}

# and later in the code:
foo "fo" ~ "o";