I'm very new to Haskell and am trying to write a simple function that will take an array of integers as input, then return either the product of all the elements or the average, depending on whether the array is of odd or even length, respectively.
I understand how to set a base case for recursion, and how to set up boolean guards for different cases, but I don't understand how to do these in concert.
arrayFunc :: [Integer] -> Integer
arrayFunc [] = 1
arrayFunc array
| (length array) % 2 == 1 = arrayFunc (x:xs) = x * arrayFunc xs
| (length array) % 2 == 0 = ((arrayFunc (x:xs) = x + arrayFunc xs) - 1) `div` length xs
Currently I'm getting an error
"parse error on input '=' Perhaps you need a 'let' in a 'do' block?"
But I don't understand how I would use a let here.
Define an auxiliary inner function like that:
arrayFunc :: [Integer] -> Integer
arrayFunc [] = 1
arrayFunc array
| (length array) % 2 == 1 = go1 array
| (length array) % 2 == 0 = go2 array
where
go1 (x:xs) = x * go1 xs
go2 (x:xs) = ((x + go2 xs) - 1) `div` length xs
This deals only with the syntactical issues in your question. In particular, [Integer] is not an array -- it is a list of integers.
But of course the name of a variable doesn't influence a code's correctness.