Hello Patrik, On Thu, Jul 12, 2018 at 12:05:52PM +0200, mrx wrote:
Why is the type class called `Read`? What am I missing above?
we can say any instance of `Read` has to implement read :: Read a => String -> a -- the actual instance implements a different function, -- but that's not relevant for our example So, a typeclass (Read, capital `r`) gives us a function (`read`, lower-case `r`). The function goes from `String` (and no other things) to our implemented type. As you discovered, the conversion happens at runtime, the compiler has no way to check it beforehand, and things might explode during execution λ> read "18" :: Char *** Exception: Prelude.read: no parse λ> read "diciotto" :: Int *** Exception: Prelude.read: no parse It is often a good idea to use `readMay` (from Safe) to handle failures locally without throwing an exception readMay :: Read a => String -> Maybe a Does this answers your question? If you have any further doubts, shoot again -F