sub context {
    print
        defined wantarray
        ? wantarray ? "list" : "scalar"
        : "void"
        , "\n";
    $_[0];
}

($a, $b) = (context('a'), context('b'));
print "a=[$a],b=[$b]\n\n";

($a, $b) = (context('a'), context('b')) || die "foo";
print "a=[$a],b=[$b]\n";

list
list
a=[a],b=[b]

void
scalar
a=[b],b=[]