My questions for bolt12's Article on Denotational Semantics

dd-questions.md

Questions on https://github.com/bolt12/advent-of-haskell-dd

In the the section "Calculating an implementations":

1. I'm not sure if I undertand the paragraph under the 'IsStack' class definition. If I try to use my own words I understood it as:

   You can get Functor implementation for s for free by using using two facts

   • the Homomorhism Property for mu: mu (fmap f s) = fmap f (mu s)
   • mu and mu' are inverse

   Is that correct?

2. I'm puzzled by this result:

-- Result:
-- fmap f []    = []
-- fmap f (h:t) = f h : t

Does this mean f would only get applied to head? Isn't that an incorrect Functor implementation for a stack?