DP problem to check if a string is the result of interleaving two strings

interleave.hs

import Data.Map qualified as M
import Data.List qualified as L

is_interleaved :: String -> String -> String -> Bool
is_interleaved a b inte = let alen = length a
                              blen = length b
                              k x y 
                                | (x == alen) = drop y b == drop (x+y) inte
                                | (y == blen) = drop x a == drop (x+y) inte
                                | otherwise = ((a L.!! x == dest_elem) && ds M.! (x + 1,y)) || ((b L.!! y == dest_elem) && ds M.! (x ,y + 1)) 
                                               where dest_elem = inte L.!! (x+y)
                              ds = M.fromList [((x,y),k x y) | x <- [0..alen], y <-[0..blen]]
                          in k 0 0 

testCases :: [(String, String, String)]
testCases = [("al","pha", "alpha"), ("banana", "ananas", "bananaananas"), ("dynamic", "programming", "prodgyrnamammiincg")]

main = putStrLn . show . map (\(x,y,z) -> is_interleaved x y z) $ testCases