I was just musing the other day about the possibility of allowing (efficient and transparent) destructive updates in certain situations. Take the following (giberish) example: f xs = g xs [] where g [] ac = ac g (x1:x2:xs) ac = g xs (ac ++ [x2,x1]) It seems to me that the list concatenation in the tail recursion call can be safely performed destructively. Does anybody know about any research going on in this area? (Mind you: no linear types, no monads, only `under the hood' compiler optimization.) I'm aware of the fact that this would imply another kind of overloading (destructive vs. non-destructive) for functions which also seems an interesting research area. Regards, -- Lajos Nagy Computer Science Ph.D. Student, Florida Institute of Technology