List comprehensions

Raku has single-dimensional list comprehensions that fall out naturally from nested modifiers; multidimensional comprehensions are also supported via the cross operator; however, Raku does not (yet) support multi-dimensional list comprehensions with dependencies between the lists, so the most straightforward way is currently:

my $n = 20;
say gather for 1..$n -> $x {
         for $x..$n -> $y {
           for $y..$n -> $z {
             take $x,$y,$z if $x*$x + $y*$y == $z*$z;
           }
         }
       }

Output:

((3 4 5) (5 12 13) (6 8 10) (8 15 17) (9 12 15) (12 16 20))

Note that gather/take is the primitive in Raku corresponding to generators or coroutines in other languages. It is not, however, tied to function call syntax in Raku. We can get away with that because lists are lazy, and the demand for more of the list is implicit; it does not need to be driven by function calls.