Haskell Non type-variable argument Error -


so function im writing supposed take in amount of points (punkte) , bonus points , compair punkte list , return corresponding grade (noten list).

im new haskell , bad @ interpreting errors.

i infinite type error never know why. can please explain me ? , maybe give solution?

function:

import data.char -- know don't need far import data.list import data.maybe  punkte = [50,54..86]  noten = [4.0,3.7,3.3,3.0,2.7,2.3,2.0,1.7,1.3,1.0]  berechnenote p bp     | bp > 20 = error "too many bonuspoints"     | bp < 0 = error "you can't give negative points"     | p > 100 = error "too many points"     | p < 0 = error "you can't give negative points"     | otherwise = berechnenote2 (p+bp) punkte  -- constructes infinite type aparently ? berechnenote2 p (x:xs)     | p == x = noten !! (fromjust (elemindex x p))     | p > x = berechnenote2 p xs     | p < x = noten !! (fromjust (elemindex x p))

and error 

blatt1.hs:17:48: error: • occurs check: cannot construct infinite type: ~ [a] • in second argument of ‘elemindex’, namely ‘p’   in first argument of ‘fromjust’, namely ‘(elemindex x p)’   in second argument of ‘(!!)’, namely     ‘(fromjust (elemindex x p))’ • relevant bindings include     xs :: [a] (bound @ blatt1.hs:16:20)     x :: (bound @ blatt1.hs:16:18)     p :: (bound @ blatt1.hs:16:15)     berechnenote2 :: -> [a] -> double (bound @ blatt1.hs:16:1) 

| p == x = noten !! (fromjust (elemindex x p))

from p == x, p , x of same type. let's name a.

from elemindex x p, p must of list type, [b]. x must potential element of p, must have type b.

so, a ~ [b] ~ [a], nonsense: list can not contain elements of same list type.

also, recommend provide intended type every top-level definition. in way, ghc produce better type errors, pointing out differences between type intend define, , type instead results our code.


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