[Haskell-beginners] Exercise 7.2a

[Francesco Ariis]

Hello Trent,

On Wed, Aug 15, 2018 at 10:08:29AM -0700, trent shipley wrote:
> Also, at this point I am having trouble reading these function declarations.
> 
> all :: (a -> Bool) -> [Bool] -> Bool
> all b ls = and (map b ls)

There must be a typo in the text. The correct signature is

    all :: (a -> Bool) -> [a] -> Bool

Which is logical:
    - we take a list of `a`s (`[a]`)
    - we pass them through a function `a -> Bool`,
      obtaining `[Bool]`
    - we check if the resulting list is all comprised of `True`s.

Does that help?