fixed check and error message for stop-when; Closes PR14009

pkgs/htdp-pkgs/htdp-lib/2htdp/private/clauses-spec-aux.rkt

@@ -34,8 +34,8 @@
 (define ip> string>)
 
 ;; Symbol X Nat -> X
-(define (proc> tag f ar)
-  (check-proc tag f ar "first" (if (> ar 1) (format "~a arguments" ar) "one argument"))
+(define (proc> tag f ar #:place (place "first"))
+  (check-proc tag f ar place (if (> ar 1) (format "~a arguments" ar) "one argument"))
   f)
 
 ;; Symbol X (Number -> Boolean) String String -> X

pkgs/htdp-pkgs/htdp-lib/2htdp/universe.rkt

@@ -112,7 +112,7 @@
               #:except
               [(_ stop? last-picture)
                #'(list (proc> 'stop-when (f2h stop?) 1)
-                       (proc> 'stop-when (f2h last-picture) 1))])]
+                       (proc> 'stop-when (f2h last-picture) 1 #:place "second"))])]
   ;; (U #f Any)
   ;; -- should the session be recorded and turned into PNGs and an animated GIF
   ;; -- if the value is a string and is the name of a local directory, use it! 

pkgs/htdp-pkgs/htdp-test/2htdp/xtest

@@ -10,6 +10,7 @@ run() {
 
 cd tests 
 
+run stop-when-error.rkt
 run key-error.rkt
 run run-movie.rkt
 run bad-draw.rkt