lispdoc - results for array-has-fill-pointer-p

(array-has-fill-pointer-p array)

Function: Return T if the given ARRAY has a fill pointer, or NIL otherwise.

Example:

(defun maybe-set-fill-pointer (array new-length)
  "If this is an array with a fill pointer, set it to
  new-length, if that is longer than the current length."
  (if (and (arrayp array)
           (array-has-fill-pointer-p array))
      (setf (fill-pointer array)
              (max (fill-pointer array)
                   new-length))))

Mentioned in:
CLtL2 - 17.5. Fill Pointers
HyperSpec - Function ARRAY-HAS-FILL-POINTER-P