You got me. I was too lazy to implement the return stack. But it should be fully possible. The hardest part was not implementing things in the trait system, but

You got me. I was too lazy to implement the return stack. But it should be fully possible. The hardest part was not implementing things in the trait system, but parsing any non-trivial syntax using the clunky macro_rules!. For this reason if/else/then are not a special syntax but words that block and unblock subsequent word execution.