Laws for Show and Read?

Sven Panne svenpanne at
Wed Jun 5 18:55:58 UTC 2019

Am Mi., 5. Juni 2019 um 17:02 Uhr schrieb David Feuer <david.feuer at

> 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?
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