[Haskell-cafe] Foldl

ClareZako zacara at gmail.com
Fri Nov 24 06:07:20 EST 2006

i'd like to write a function that given a list like [1,2,3,4...]
returns a list of couple where the first element is the corresponding
element of the string, and the second is the sum of the previous
An example:
input: [1,2,3,4]
output: [(1,0)(2,1)(3,3)(4,6)]

The problem is that I'd like to use foldl and a solution like:
buildCouples = snd . foldl op (0,[])
               op (v,xs) x = (v+x,xs++[(x,v)])
is not good since the operator ++ let the function take 2*n time and not n.

Can anyone help me please?

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