[Haskell-beginners] The type class Read

[Francesco Ariis]

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