Hi,
I am trying to write a partition function where we pass group sizes and the list we want to partition into groups
as arguments and get back a list of groups (or list of lists in this case). My first attempt was by using an auxiliary inner function
{-# LANGUAGE ScopedTypeVariables #-}
module Partition where
partition :: [Int] -> [a] -> [[a]]
partition ds ps = reverse $ paux ds ps []
where
paux :: [Int] -> [a] -> [[a]] -> [[a]]
paux [] [] ps' = ps'
paux [] ps ps' = [ps] ++ ps’
paux _ [] ps' = ps'
paux (d:ds') ps ps' = paux ds' (snd (splitAt d ps)) ([fst (splitAt d ps)] ++ ps')
——————
*Partition> partition [2, 3] [1,2,3,4,5]
[[1,2],[3,4,5]]
*Partition> partition [1, 2] [1,2,3,4,5]
[[1],[2,3],[4,5]]
*Partition> partition [1, 2, 5] [1,2,3,4,5]
[[1],[2,3],[4,5]]
I was speculating if we could write the same function using foldl function but haven’t been able to figure it out.
I would really appreciate if you can give me pointers on how we can implement it.
partition' :: [Int] -> [a] -> [[a]]
partition' [] ds = [ds]
partition' ps ds = foldl ??? ???' ???''
contrary to my speculation is it even possible to write such a function using foldl if so why not?
Regards,
Apoorv Ingle
Graduate Student, Computer Science
apoorv.ingle(a)ku.edu <mailto:apoorv.ingle@ku.edu>
