From language/functions

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callsame calls the next matching candidate with the same arguments that were used for the current candidate and returns that candidate's return value.

proto a(|) {*}
 
multi a(Any $x) {
    say "Any $x";
    return 5;
}
 
multi a(Int $x) {
    say "Int $x";
    my $res = callsame;
    say "Back in Int with $res";
}
 
a 1;        # OUTPUT: «Int 1␤Any 1␤Back in Int with 5␤»