Accumulating within monadic contexts without folds

{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
{-# HLINT ignore "Use void" #-}
{-# HLINT ignore "Use map" #-}
{-# HLINT ignore "Use foldl" #-}
 
main :: IO ()
main =
    do
        print (f1a [3, 2, 6, 8])
        f1b [3, 2, 6, 8]
        f1c [3, 2, 6, 8] >>= print >> return ()
        print (f2a [] [3, 2, 6, 8])
        f2b [3, 2, 6, 8]
        f2c [] [3, 2, 6, 8] >> return ()
 
f1a :: [Int] -> [Int]
f1a [] = []
f1a (n:rln) = (n + 1) : f1a rln
 
f1b :: [Int] -> IO ()
f1b ln = f1' ln >>= print
    where
        f1' :: [Int] -> IO [Int]
        f1' [] = return []
        f1' (n:rln) = f1' rln >>= (\r -> return ((n + 1) : r))
 
f1c :: [Int] -> IO [Int]
f1c [] = return []
f1c (n:rln) = f1c rln >>= (\r -> return ((n + 1) : r))
 
f2a :: [Int] -> [Int] -> [Int]
f2a lnAccu [] = lnAccu
f2a lnAccu (n:rln) = f2a (n + 1 : lnAccu) rln
 
f2b :: [Int] -> IO ()
f2b ln = f2b' [] ln >>= print
    where
        f2b' :: [Int] -> [Int] -> IO [Int]
        f2b' lnAccu [] = return lnAccu
        f2b' lnAccu (n:rln) = f2b' ((n + 1) : lnAccu) rln
 
f2c :: [Int] -> [Int] -> IO [Int]
f2c lnAccu [] = print lnAccu >> return lnAccu
f2c lnAccu (n:rln) = f2c ((n + 1) : lnAccu) rln