User-oriented stack traces

usertrace.pl

my role Described[$by] {
    method description() { $by }
}
multi sub trait_mod:<is>(Routine:D $r, :$descr!) {
    $r does Described[$descr];
}

sub save-state() is descr('saving program state') {
    save-all();
}
sub save-all() {
    save-config();
}

sub save-config() is descr('saving user config') {
    my $f = open :w, '/no/such/path';
}

try save-state();
if $! {
    say "Error: $!.message()";
    for $!.backtrace.list {
        if .code.^can('description') {
            say "  while ", $_.code.description()
        }
    }
}

x-output

Error: Unable to open filehandle from path '/no/such/path'
  while saving user config
  while saving program state