I've been slowly making my way through Yet Another Haskell Tutorial. As
a first introduction to the language it doesn't seem bad at all.
However, I'm wondering about the proposed solution to exercise 9.2. The
text itself suggests using instance Monad (Either String) where, so I
arrived at
Quick fix: add this line to the top of your file
{-# OPTIONS -fglasgow-exts #-}
Having String instead of a free type variable is beyond the basic
limitations of Haskell's type classses.
However, enabling the very common Glasgow extensions expands the rules
to admit your definition. If you for
