Hi! I have a "low-level" function for insertion element into mutable vector. It looks like this: place :: (PrimMonad m) => MV.MVector (PrimState m) (Int, t) -> (Int, t) -> Int -> m () place v max@(val1,_) i = place' i where place' i = do let j = i - 1 if j < 0 then return () else do curr@(val2, _) <- MV.unsafeRead v j -- <<<<< if val2 > val1 then do MV.unsafeWrite v j max MV.unsafeWrite v i curr place' j else return () It searches a right place for the i-th element, moving it towards beginning . Surprisingly, it works, but is slow. Time profiling says this: COST CENTRE MODULE %time %alloc ticks bytes place.place' Main 40.1 77.1 9167 12169223232 And heap profiling says that most of allocations are for Int and (,). I think, binding of unsafeRead to curr and val might allocate my Precious memory more than, maybe, it is needed. Am I right? Is it some strictness that I need? Is there anything I can do in this situation? Or should I look outside of this function? PS Emergence of this piece of code is a long story. Originally I was trying to solve Project Euler's problem 411. But now it is a different issue.