Auto-derived Show instance not terminating

[fiddlerwoaroof]

Running this program (or just running (show q) in a REPL) never terminates.

#lang hackett

(data (Cons a b)
  Nil
  (Cons a (Cons b a))
  #:deriving [Show])

(def q
  (Cons 1
        (Cons "3"
              Nil)))

(main
 (println (show q)))```

[lexi-lambda]

I think this is essentially the same bug as #89, but I’m not completely sure. The issue seems to be that, when solving Show (Cons b a), the typechecker isn’t smart enough to realize it doesn’t need to solve Show (Cons a b) again, since that’s the constraint it’s currently solving, and it should simply tie the knot instead.

[fiddlerwoaroof]

Yeah, I thought #89 looked similar but wasn't sure because that one involved a more complicated situation (classes + instances) while this was a fairly simple datatype.