sub foo ($$;$) { ... }

my $curried_foo = foo( 1 );
my $return_value = foo( 1, 2 );

##</code><code>##

sub foo ($$;$) { ... }

to

sub foo
{
    if (@_ < 2) {
      my $arg = shift;
      return sub { foo($arg, @_) };
    }

    ...
}