Re: [Haskell-cafe] Question on nested fmaps.

This is one of the functor laws, the other one being `fmap id = id'. If it doesn't hold your type *should* not have a Functor instance, but the compiler doesn't verify this for you. HTH, Adam On Thu, Dec 31, 2015 at 2:15 AM, David Banas wrote:

Is this true, in general?:

fmap h (fmap g f) == fmap (h . g) f

Is there a simple proof?

Thanks, -db

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