Haskell - Parse error on input '->'

Question

I created this program to return a list of positions of a matrix that no has zero value.

This Code:

type Pos = (Int,Int)
type Matrix = [[Int]]

v0 [Pos]->Matrix->[Pos]
v0 [] m =[]
v0 [p:ps] m = if ((takeH m p) == 0) then v0 ps m
                                    else p:v0 ps m

takeH:: Matrix->Pos->Int
takeH m (i,j)= (m!!(i-1))!!(j-1)

Produces this error:

Parse error on input '->'
Failed,modules loades: nome.

Why ?

I hope that I've been clear.

Answer 1

You need :: before the type of a function.

-- vv here
v0 :: [Pos] -> Matrix -> [Pos]
v0 [] _ = []
-- v    v also parenthesis, not square brackets
v0 (p:ps) m = if ((takeH m p) == 0) then v0 ps
                                    else p:v0 ps