Currying in Perl 6

There is still quite a lot of low-hanging fruit in Rakudo.

I checked on IRC today during a break in the class I'm teaching to see jhorwitz asking for currying in Perl 6, which is spelled like:

my $curried = &function.assuming(...);

A few minutes later, I committed an implementation of it. Here is the currying patch for Rakudo. It's about the same size as the last patch I mentioned here. Here are the tests we're now passing:

sub tester(:$a, :$b, :$c) {
"a$a b$b c$c";
}

my $u = &tester.assuming(b => 'x');
is $u(a => 'w', c => 'y'), 'aw bx cy', 'currying one named param';

my $w = &tester.assuming(b => 'b');
my $v = $w.assuming(c => 'c');
is $v(a => 'x'), 'ax bb cc', 'can curry on an already curried sub';
is $w(a => 'x', c => 'd'), 'ax bb cd', '... and the old one still works';