Error passing parameters through haskell function -

i'm receiving error , don't know why.

mapo :: ((float, float) -> float) -> [(float, float)] -> [float] mapo f [] = [] mapo f (x:y) = f x : mapo f y 

compiles ok.

*main> mapo + [(1,2)]  couldn't match type `(float, float) -> (float, float)' `float' expected type: (float, float) -> float   actual type: (float, float) -> (float, float) -> (float, float) in first argument of `mapo', namely `(+)' in expression: mapo (+) [(1, 2)] in equation `it': = mapo (+) [(1, 2)] 

the purpose of function receive operator (let's + or -), list of pairs of numbers (float) , return result of using operator each of pairs of parameters of list.

your problem merely syntactic error; when want partially apply operator need wrap in parentheses; instead of

mapo + [(1,2)] 

write

mapo (+) [(1,2)] 

otherwise parses adding mapo [(1,2)] (i.e. (+) mapo [(1,2)] not want.

next thing getting type right:

(+) :: float -> float -> float (in case, real type more general) - function wants (float,float) -> float. these 2 types aren't equal, express pretty same thing can map between them curry :: ((a,b) -> c) -> -> b -> c , uncurry :: (a -> b -> c) -> (a,b) -> c functions. in case need pass uncurry (+) mapo function.