[Haskell-beginners] Re: question about styles of recursion

[7stud]

Daniel Fischer <daniel.is.fischer <at> web.de> writes:
> 
> >  myAvg' :: Int -> [Int] -> [ Double ] -> Double
>>
> >  myAvg' sum count []     = sum / fromIntegral count
> >  myAvg' sum count (x:xs) = myAvg' (x + sum) (n + 1) xs
> 
> 
> > ehask.hs:2:24:
> >     Couldn't match expected type `Double' against inferred type `Int'
> >     In the expression: s / fromIntegral count
> >     In the definition of `myAvg'':
> >         myAvg' s count [] = s / fromIntegral count
> > Failed, modules loaded: none.
> >
> 
> Yup, the type signature is wrong, it should be
> 
> myAvg' :: Double -> Int -> [Double] -> Double
> 

Can you explain the error message in detail?  To me it looks like 
this should be the problem:

Prelude> fromIntegral [1, 2, 3]

<interactive>:1:0:
    No instance for (Integral [t])
      arising from a use of `fromIntegral' at <interactive>:1:0-21
    Possible fix: add an instance declaration for (Integral [t])
    In the expression: fromIntegral [1, 2, 3]
    In the definition of `it': it = fromIntegral [1, 2, 3]