Remove duplicates from a list

Just wanted to share my solution to this common problem.

(defun nub (l "l")
  (let ((table (makeTable "" nil)))
    (foreach e l table[e] = t)
    table->?))

Output:

(nub (parseString "Banana Rama" "")) => ("a" "m" "n" "R" "B" " ")

This assumes order doesn't matter. If order does matter (and efficiency doesn't...), you could use this O(n^2) version, which is a literal translation of the one in the Haskell Data.List library:

(defun nub (l "l")
  (defun _nub (xs ls "ll")
    (unless (null xs)
      (destructuringBind (x @rest xs) xs
        (if (member x ls)
            (_nub xs ls)
          (cons x (_nub xs (cons x ls)))))))
  (_nub l nil))

Output:

(nub (parseString "Banana Rama" "")) => ("B" "a" "n" " " "R" "m")

If you want to preserve order and get O(n) performance, you could modify the last version to use a table instead of a list:

(defun nub (l "l")
  (defun _nub (xs ls "lo")
    (unless (null xs)
      (destructuringBind (x @rest xs) xs
        (if (ls[x])
            (_nub xs ls)
          (cons x (_nub xs (ls[x] = t && ls)))))))
  (_nub l (makeTable "" nil)))

Output:

(nub (parseString "Banana Rama" "")) => ("B" "a" "n" " " "R" "m")