Haskell partial sum of a list error

Question

I need to write a function in Haskell that sums the elements of a list until some specific elements stored in another list.

For example partial_add [1,2,3,4,5,

Answer 1

Given your example, I would write the function something like this:

partialAdd :: [Int] -> [Int] -> [Int]
partialAdd ls seps = foldr f [] ls
  where 
    f a [] = [a]
    f a (x:xs)
      | a `elem` seps = a:x:xs
      | otherwise = (x+a):xs

*Main> partialAdd [1,2,3,4,5,6] [2,5]
[3,12,6]

Btw. I think the solution in your question seems not to work quite the way you specified in your example (or I misunderstood something):

partial_add :: [Int] -> [Int] -> Int -> [Int]
partial_add [] _ count = []
partial_add (a:x) list count | elem a list =  count:partial_add x list 0
                             | otherwise =  partial_add x list (count+a)

*Main> partial_add [1,2,3,4,5,6] [2,5] 0
[1,7]

But it is easily fixed to work for your example:

partial_add :: [Int] -> [Int] -> Int -> [Int]
partial_add [] _ count = [count]
partial_add (a:x) list count | elem a list =  (count+a):partial_add x list 0
                             | otherwise =  partial_add x list (count+a)

*Main> partial_add [1,2,3,4,5,6] [2,5] 0
[3,12,6]