[Haskell-cafe] Question on nested fmaps.
adam at bergmark.nl
Thu Dec 31 01:27:05 UTC 2015
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.
On Thu, Dec 31, 2015 at 2:15 AM, David Banas <capn.freako at gmail.com> wrote:
> Is this true, in general?:
> fmap h (fmap g f) == fmap (h . g) f
> Is there a simple proof?
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