Those are not demonstrations of the defaulting rules in action though.

As far as I know, :t is agnostic to those and will keep showing the original polymorphic version, since you're not in a context where GHC has to sacrifice the polymorphic type and commit to a monomorphic one using a default, like when expressions are evaluated.

Also I think that's effective just for the REPL (it uses extended defaulting rules that are more lax) and is done for convenience. If it was during a GHC build, you'd get loud warning when something is defaulted.

Try `reverse []` for fun vs. `:t reverse []`.