Question

How can I delete the element elem in list L? If the list does not contain elem, then the function should return the list unchanged.

For instance:

L = [1, 3, 4, 0, 5, 7]    
elem = 5

So far I have the following function:

fun removeElem elem myList[] = myList
  | removeElem (myList::tl) = if mem myList elem then
                                rm elem myList[]
                              else
                                removeElem elem tl

Answer 1

You can turn the question around and ask how to keep only those items not equal to elem. This fits cleanly with filter:

fun removeElem elem myList = filter (fn x => x <> elem) myList