Earlier quoted context omitted.
Did you respect indentation? Tutorial is really failing here with this “just paste this to the bottom”.
I did respect indentation, and here's what I get as an error: > tutorial.hs:21:23: Illegal type signature: `[Person] people' Perhaps you intended to use -XScopedTypeVariables In a pattern type-signature
For example, if you have
let people :: [Person] people
instead of let people :: [Person]
people = -- ...
that would give you that error.