Lisp SBCL declare a function argument to be a list of a certain type for type checking

Question

I am having a hard time figuring out how to tell the sbcl compiler that the &rest args to a function ought to be a list of TYPE.

Basically, I want to turn something like this:

    (defun g (f1 &rest fn)
      (declare (function f1) (list fn)) ... )

To something like this:

    (defun g (f1 &rest fn)
      (declare (function f1) (list-of-fixnums-type? fn)) ... )

I figured I could do this:

    (defun g (f1 fn)
      (declare (function f1) (type (vector function) fn) ... )

But I'd have to use a vector instead of a list. I know I can use predicates but then It wouldn't do it at compile time and I'd have to throw an error manually.

Is what I am trying to do possible?

I am using SBCL 1.3.15

Answer 1

You can specify a type for rest arguments when you declare the ftype of the function.

(declaim (ftype (function (function &rest fixnum) t)
                foo))
(defun foo (f &rest nums)
  (funcall f nums))

(defun bar ()
  (foo #'princ 345 -432 23 "45" 54)) ; warning: Constant "45" conflicts with its asserted type FIXNUM