Suppress warning for function arguments not used in LISP

Question

In lisp, I need to define a set of functions, all with the same number of arguments. However, the functions may or may not use all the arguments, leading to a spur of warnin

Answer 1

See the Common Lisp Hyperspec: Declaration IGNORE, IGNORABLE

A variable is not used. Ignore it.

(defun true (x y)
  (declare (ignore y))
  x)

Above tells the compiler that y is not going to be used.

The compiler will complain if it is used. It will not complain if it is not used.

A variable might not be used. Don't care.

(defun true (x y)
  (declare (ignorable y))
  x)

Above tells the compiler that y might not be used.

The compiler will not complain if it is used and also not if it is not used.