Laws for Show and Read?

[David Feuer]

We already have the law

  read . show = id

which implies the injectivity and surjectivity conditions you specify.

On Wed, Jun 5, 2019, 3:45 AM Dannyu NDos <ndospark320 at gmail.com> wrote:

> Shouldn't it be laws that "show" must be injective and "read" must be
> surjective? Without such laws, one could define:
>
> data Foo = Foo
> instance Show Foo where
>     show _ _ = id
> instance Read Foo where
>     readPrec = pfail
>
> which should be prevented.
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