Problem is \:get_attr_str() not implemented in class 'Coroutine'current instr.: 'print_exception' pc 111585 (src/gen/CORE.setting.pir:50152) (src/gen/CORE.setting:9760) #raku

permutations.raku

# We recursively.generate permutations
# Here is one step of the recursion :
# Given a array @l, $e is its first element and @m the array @l minus $e. We
# get the permutations of @l by getting all the permutations of @m. For each
# such permutation, we alternatively insert $e in each possible position obtaining
# @m+1 arrays.

sub permutations(*@l is copy) {
  gather {
    if @l == 1 {
      take @l;
    } else {
      while (my $e = @l.shift) {
#        say "=@l[]";
#        say $e;
        for permutations(@l) -> @p {
          for 0..@p {
            my @r = @p;
            @r.splice: $_, 0, $e;
#            say "?@r[]";
            take @r;
          }
        }
      }
    }
  }
}

my @a = permutations 1;
say "done: @a[]";
@a = permutations 1..4;
say "done: @a[]";

=begin END

proto sub fact($i) { ... }
multi sub fact(0)  { 1 }
multi suv fact($n) { $n * fact($n-1)}

+uniq permutations(5) == fact 5

the problem was solved by moving the return outside the gather.
thx @jnthn.
the program is not yet correct.
I will submit the correct program as a pullt request to the rakudo repository

In the new version, I am stuck again with the same problem

I may have hit a limit of the current implementaton
[14:54] cognominal: iirc [Coke] has hit another limitation of gather/take recentely; if you reuse the same gather/take block, the first iterator has to be exhausted before the second one is started

see http://irclog.perlgeek.de/perl6/2013-04-25#i_6745999