Re: Laws for Show and Read?

Sven Panne wrote:

We already have the law read . show = id which implies the injectivity and surjectivity conditions you specify.

I think this doesn't hold for the standard Read/Show instances for Double/Float: IEEE-754 NaNs have a sign bit and a payload, and both parts are probably lost by the "read . show"-combination. The 2 infinities are probably OK, but what about -0 vs. +0?

ghci> show (-0 :: Double) "-0.0" ghci> read (show (-0 :: Double)) :: Double -0.0 It's true that extra information in NaNs is lost, but they all behave the same anyway... Cheers, Bertram