[Haskell-beginners] Maybe a -> Maybe b

Imants Cekusins imantc at gmail.com
Fri Aug 25 12:56:41 UTC 2017

> as an exercise, you can try to figure out the implementation

.. time is up :-P
Here is an answer for slightly more generic Proxy and f:

data Proxy a = Proxy a

exProxy::Functor f =>
     f (Proxy a) -> f a
exProxy = (un1 <$>)
    where un1 (Proxy a1) = a1

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