Laws for Show and Read?

Dannyu NDos ndospark320 at
Wed Jun 5 07:45:17 UTC 2019

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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