(rutils.iter:iter
	 (:for item :in-vector #(1 2 3 4 5))
	 (format t "Hi ~A~%" item))

(rutils.iter:iter
	 (:for item :in-sequence #(1 2 3 4 5))
	 (format t "Hi ~A~%" item))

The value
 NIL
is not of type
 NUMBER
 [Condition of type TYPE-ERROR]

 0: (SB-KERNEL:%NEGATE NIL)
 1: (- NIL)
 2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (- NIL) #<NULL-LEXENV>)
 3: (EVAL (- NIL))
 4: (RUTILS.ITER::RETURN-SEQ-CODE :ELEMENT-VAR ITEM :SEQUENCE #(1 2 3 4 5) :ACCESS-FN AREF :SIZE-FN #<unavailable argument> :ELEMENT-TYPE NIL :SEQUENCE-TYPE #<unavailable argument> :FROM #<unavailable arg..
 5: (RUTILS.ITER::APPLY-CLAUSE-FUNCTION #<unavailable argument> #<unavailable argument>)
 6: (RUTILS.ITER::PROCESS-CLAUSE #<unavailable argument>)
 7: (RUTILS.ITER::WALK-LIST-NCONCING #<unavailable argument> #<FUNCTION RUTILS.ITER::WALK> #<FUNCTION (LAMBDA (RUTILS.ITER::FORM RUTILS.ITER::BODY) :IN "/home/piknik/.local/share/common-lisp/source/rutils..
 8: ((MACRO-FUNCTION RUTILS.ITER:ITER) #<unavailable argument> #<unavailable argument>)
 9: ((FLET SB-IMPL::PERFORM-EXPANSION :IN MACROEXPAND-1) #<FUNCTION (MACRO-FUNCTION RUTILS.ITER:ITER) {52A7C70B}> NIL)
 10: (MACROEXPAND (RUTILS.ITER:ITER (:FOR ITEM :IN-VECTOR #(1 2 3 4 5)) (FORMAT T "Hi ~A~%" ITEM)) #<NULL-LEXENV>)
 11: (SB-INT:SIMPLE-EVAL-IN-LEXENV (RUTILS.ITER:ITER (:FOR ITEM :IN-VECTOR #(1 2 3 4 5)) (FORMAT T "Hi ~A~%" ITEM)) #<NULL-LEXENV>)
 12: (EVAL (RUTILS.ITER:ITER (:FOR ITEM :IN-VECTOR #(1 2 3 4 5)) (FORMAT T "Hi ~A~%" ITEM)))

(rutils.iter:iter
	 (:for item :in '(1 2 3 4 5))
	 (format t "Hi ~A~%" item))
Hi 1
Hi 2
Hi 3
Hi 4
Hi 5