fixed error message for shadowing clause names; Closes PR 12621

collects/2htdp/private/clauses-spec-and-process.rkt

@@ -101,11 +101,18 @@
          (syntax-case stx ()
            [(kw . E) (kwd-in? #'kw) (begin (->rec? #'kw #'E) (cons #'kw stx))]
            [(kw . E)
-            (let ([kw (syntax-e #'kw)])
-              (if (member kw (map syntax-e kwds))
-                  (raise-syntax-error tag (format "the ~a clause appears twice" kw) stx)
-                  (raise-syntax-error tag (format "~a clauses are not allowed when using ~a" kw tag)
-                                      stx)))]
+	    (let* ([stx2 #'kw]
+		   [kw (syntax-e stx2)]
+		   [kw-appears-as-symbol
+		     (member kw (map syntax-e kwds))
+		     #;
+		     (for/or ((n kwds))
+		       (symbol=? kw (syntax-e n)))])
+              (if kw-appears-as-symbol
+                  (raise-syntax-error
+		    tag (format "the ~a keyword seems to have been used as a variable" kw) stx2)
+                  (raise-syntax-error
+		    tag (format "~a clauses are not allowed within ~a" kw tag) stx)))]
            [_ (raise-syntax-error tag "expected a clause, but found something else" stx)]))
        stx:list))
 

collects/2htdp/tests/on-tick-defined.rkt

@@ -1,4 +1,4 @@
-#lang scheme/load
+#lang racket/load
 
 ;; purpose: when on-tick or on-xxx has been redefined, 
 ;; --- raise more specific error message
@@ -6,8 +6,8 @@
 
 (error-print-source-location #f)
 
-(define legal "big-bang: ~a clauses are not allowed when using big-bang")
-(define double "big-bang: the on-tick clause appears twice")
+(define legal "big-bang: ~a clauses are not allowed within big-bang")
+(define double "big-bang: the on-tick keyword seems to have been used as a variable")
 (define atleast "big-bang: expects a [to-draw handler] clause, missing")
 
 ;; is the mandatort to-draw clause specified 

collects/2htdp/tests/on-tick-universe-with-limit.rkt

@@ -4,5 +4,5 @@
 
 (universe 0 
           (on-tick (lambda (w) (make-bundle (add1 w) '() '())) 1/28 3)
-          (on-msg void)
+          (on-msg (lambda (w sender msg) (make-bundle w '() '())))
           (on-new cons))