Say I have a function that takes a list and does something:
(defun foo(aList)
(loop for element in aList ...))
But if the list is nested I want to flatten it first before the loop does stuff, so I want to use another function (defun flatten(aList)) that flattens any list:
(defun foo(flatten(aList))
(loop for element in aList ...))
Lisp doesn't like this. Is there another direct way around this?
Here's one way:
(defun foo (alist)
(loop for element in (flatten alist) ...)
You can pass the function as an &optional argument.
(defun foo (alist &optional fn)
(if (not (null fn))
(setf alist (funcall fn alist)))
(dostuff alist))
A sample run where dostuff just print its argument:
(foo '(1 2 (3)))
=> (1 2 (3))
(foo '(1 2 (3)) #'flatten)
=> (1 2 3)
This approach is more flexible as you are not tied to just one 'pre-processor' function.
