Hi,
(Update it is not an problem with operators in rakudo)
(Update perl5 code fails because $f and $g aren't local in my original code, as almut points out)

I was trying to create a composition operator in perl. I know it is too simple, it only accepts functions, which have 1 argument, but that isn't the problem:

sub infix:<!*> (&f, &g) {
        return sub ($x)  {
                return f(g($x));
        };
}
[download]

It works when I make a composition of 2 functions:

sub test ($x) {
        return $x ~ " test";
}


# outputs (&test !* &test) test test
say (&test !* &test)('&test !* &test');
[download]

When I try to composite 3 functions, it gets a bit wacky:

# Fails with too much recursion
say (&test !* (&test !* &test))('&test !* &test !* &test');
[download]

When I try to first assign the working case to a variable and then composite it with another function, I get an even stranger result:

my $p = &test !* &test;
my $q = $p !* &test;
# outputs $p = &test !* &test test
say $p('$p = &test !* &test');
#should be $p !* test test test (?),  but says $p !* test test
say $q('$p !*  &test');
[download]

I wrote it in a comparable way for javascript to see and perl5, if it was working there. <s>In perl5 it didn't work either</s> and in javascript it did:

(Runned with rhino)

function comp(f, g){
        return function(x){
                return f(g(x));
        }
}

function test(x){
        return x + " test";
}

print (comp(test,comp(test,test))("test "));
[download]

Failing perl5 code

sub comp {
        $f = shift;
        $g = shift;
        return sub {
                $x = shift;
                return $f->($g->($x));
        };
}
sub test {
        return (shift) . " test";
}
print comp(\&test, comp(\&test,\&test))->("test ");
[download]

Correct perl5 code

sub comp {
        my ($f, $g) = @_;
        return sub {
                my $x = shift;
                return $f->($g->($x));
        };
}
sub test {
        return (shift) . " test";
}
print comp(\&test, comp(\&test,\&test))->("test ");
[download]

The code on rosettacode.org has the same problem. (perl6)

Is this a bug, or is this something I clearly don't understand?

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