Am Donnerstag 26 März 2009 21:53:47 schrieb 7stud:
7stud
writes: myAvg' :: Int -> [Int] -> [ Double ] -> Double myAvg' sum count [] = sum / fromIntegral count myAvg' sum count (x:xs) = myAvg' (x + sum) (n + 1) xs
The length function was introduced before the sum function, which I see you are using in your function definition.
Hmm...I guess you aren't using the sum function--that's one of your variable names. I wonder how Prelude knows sum is a variable name and not the sum function?
Name shadowing/scoping. By naming one of the parameters sum, a local variable with that name is declared and Prelude.sum is only accessible qualified in that scope. It's the same as declaring local variables with the same name as one in an enclosing scope in other languages.
I changed the name sum to s, and I get this error:
Prelude Data.List> :load ehask.hs [1 of 1] Compiling Main ( ehask.hs, interpreted )
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