Types that don't implement Show can be implicitly printed

[FernandoBasso]

I have noticed that things that don't have an instance of Show can be somehow printed, or displayed if I run the buffer with C-c C-l.

Why is that? Can it be disabled? In a normal REPL (on a terminal outside of Emacs), those would give an error because data constructors for types not deriving (or implementing) Show can't be printed, and functions don't implement Show either.

I am studying trough Haskell From First Principles, and was not getting the errors when trying to display things that don't implement Show, and was confused for a while until I tried in a normal REPL. Couldn't find this behavior in the docs either.

[purcell]

Well spotted. I hadn't noticed this myself. Turns out there's special handling for this case. You can (setq haskell-interactive-types-for-show-ambiguous nil) to disable this.