Question

I’m practicing Haskell, and writing a summation function that takes in two numbers (upper and lower limits) and does the summation.

ie, summation 0 10 would return 55

I can get it mostly working, but having trouble figuring out how to get it using only two parameters.

Here is what I have so far:

summation :: Integer -> Integer -> Integer -> Integer
summation x y sum =
    if (y<x) then
        sum
    else
        summation x (y-1) (sum+y)

So this works fine, but I need to do summation 0 10 0 to get it working properly. I’m not sure how I can get this working with only two parameters in Haskell.

Answer 1

You wrap it.

summation :: Integer -> Integer -> Integer
summation x y = summation' x y 0

summation' :: Integer -> Integer -> Integer -> Integer
summation' x y sum =
    if (y<x) then
        sum
    else
        summation' x (y-1) (sum+y)