GeneralFold.hs

-- I just came up with a generalFold.
-- Is there something similar in Haskell?

generalFold :: ((info,acc) -> Maybe (info,acc)) -> (info,acc) -> (info,acc)
generalFold transition duple =
 let newDupleMaybe = transition duple
 in case newDupleMaybe of
  Nothing -> duple
  Just newDuple -> generalFold transition newDuple

sum10 = generalFold transition ([1..10],0)
 where
  transition (info,acc) =
   if (length info) <= 0 then Nothing
   else Just (tail info,(head info)+acc)

product10 = generalFold transition ([1..10],1)
 where
  transition (info,acc) =
   if (length info) <= 0 then Nothing
   else Just (tail info,(head info)*acc)

vectorToMatrix :: [Double] -> Int -> [[Double]]
vectorToMatrix vector nColumns =
 let (info,acc) = generalFold transition (vector,[])
 in acc
 where
  transition (info,acc) =
   if n < 0 then Nothing
   else Just (take n info,(drop n info):acc)
   where n = length info - nColumns

matrix3x3 = vectorToMatrix [1..9] 3