Re: Laws for Show and Read?

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@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. _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries