Haskell : "Parse error in pattern:" when creating a maximum' function

Question

So I am trying to implement a maximum function but for some reason I am getting a parse error on the last line "mymax x:y:ys = ..... " . What is the reason for that error? Thanks!

mymax :: Ord a=>[a]->Maybe a
mymax [] = Nothing
mymax [x] = Just x
mymax x:y:xs = if (x < y) 
            then mymax(y:xs) 
            else mymax(x:xs)

Possible duplicate of [Haskell: Parse error in pattern](https://stackoverflow.com/questions/8561762/haskell-parse-error-in-pattern) — Chris Martin, Sep 06 '17 at 07:53

score 3 · Accepted Answer · answered Sep 18 '13 at 04:42

3

You're missing the parentheses:

mymax (x:y:xs) = if (x < y) 
                 ...

answered Sep 18 '13 at 04:42

fjarri

9,546
39
49

score 2 · Answer 2 · answered Sep 18 '13 at 04:42

2

Put parenthesis around x:y:xs

mymax (x:y:xs) = ...

answered Sep 18 '13 at 04:42

bheklilr

53,530
6
107
163

Haskell : "Parse error in pattern:" when creating a maximum' function

2 Answers2