This mail got stuck in my spam filter because of auth reason.
Bumping in case someone else who missed it wants to answer.
2015-08-28 19:12 GMT+02:00 Williams, Wes(AWF)
Hi haskellers,
I am trying to understand why I get the following error in learning applicative style.
Prelude> let estimates = [5,5,8,8,2,1,5,2]
Prelude> (/) <$> Just $ foldl (+) 0 estimates <*> Just . fromIntegral $ length estimates
<interactive>:54:1:
Non type-variable argument in the constraint: Fractional (Maybe r)
(Use FlexibleContexts to permit this)
When checking that ‘it’ has the inferred type
it :: forall a r.
(Fractional (Maybe r), Num a, Num (Int -> Maybe a -> r)) =>
Maybe r -> Maybe r
All the parts work individually. If use let and assign the parts to x and y it also works.
E.g. This works let x = Just $ foldl (+) estimates Let y = Just . fromIntegral $ length estimates (/) <$> x <*> y
I clearly do not understand exactly how these work. :-)
Thanks for any help, -wes
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