gistfile1.txt

(gdb) bt
#0  0x00007ffff79a453b in MVM_gc_root_add_frame_roots_to_worklist () from /home/larry/nom/install/lib/libmoar.so
#1  0x00007ffff79a36bd in MVM_gc_worklist_mark_frame_roots () from /home/larry/nom/install/lib/libmoar.so
#2  0x00007ffff79a514a in process_worklist () from /home/larry/nom/install/lib/libmoar.so
#3  0x00007ffff79a53b4 in MVM_gc_collect () from /home/larry/nom/install/lib/libmoar.so
#4  0x00007ffff79a2a13 in run_gc () from /home/larry/nom/install/lib/libmoar.so
#5  0x00007ffff79a3238 in MVM_gc_enter_from_allocator () from /home/larry/nom/install/lib/libmoar.so
#6  0x00007ffff79a3361 in MVM_gc_allocate_nursery () from /home/larry/nom/install/lib/libmoar.so
#7  0x00007ffff79a33ad in MVM_gc_allocate_zeroed () from /home/larry/nom/install/lib/libmoar.so
#8  0x00007ffff79a34ed in MVM_gc_allocate_object () from /home/larry/nom/install/lib/libmoar.so
#9  0x00007ffff79b056b in MVM_repr_alloc_init () from /home/larry/nom/install/lib/libmoar.so
#10 0x00007ffff580ec20 in p6listitems () from /home/larry/nom/install/languages/perl6/runtime/dynext/libperl6_ops_moar.so
#11 0x00007ffff798b0b7 in MVM_interp_run () from /home/larry/nom/install/lib/libmoar.so
#12 0x00007ffff79f5e23 in MVM_vm_run_file () from /home/larry/nom/install/lib/libmoar.so
#13 0x0000000000400f26 in main ()

This is from:

{
    multi sub cbal-tree(0){ Any }
    multi sub cbal-tree(Int $n) {
	my @r;
        do {
            if $n % 2 == 1 {
                my $k = ($n - 1) div 2;
                for cbal-tree($k) -> $a {
                    for cbal-tree($k) -> $b {
                        @r.push: ['x', $a, $b];
                    }
                }
            } else {
                my $k = $n div 2;
                for cbal-tree($k) -> $a {
                    for cbal-tree($k - 1) -> $b {
                        @r.push: ['x', $a, $b];
                    }
                }
                for cbal-tree($k - 1) -> $a {
                    for cbal-tree($k) -> $b {
                        @r.push: ['x', $a, $b];
                    }
                }
            }
        }
	@r;
    }

    say +cbal-tree(4);
}

{
    sub heights(Any $x) {
        return 0 unless $x;
	my @results;
        do {
            for heights($x[1]) { @results.push: 1 + $_ };
            for heights($x[2]) { @results.push: 1 + $_ };
        }
	@results;
    }

    sub is-hbal($x) {
        my @heights = heights($x).sort;
        @heights[*-1] - @heights[0] <= 1;
    }

    multi sub hbal-tree(0) { Any }
    multi sub hbal-tree(1) { ['x', Any, Any] }
    multi sub hbal-tree(Int $n) {
        gather {
            for hbal-tree($n - 1) -> $a {
                for hbal-tree($n - 1) -> $b {
                    take ['x', $a, $b];
                }
                for hbal-tree($n - 2) -> $b {
                    if is-hbal(['x', $a, $b]) {
                        take ['x', $a, $b];
                        take ['x', $b, $a];
                    }
                }
            }
        }
    }

    my @results = hbal-tree(3);
    for ^15  {
	say is-hbal(@results[$_]);
    }
}