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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