use namespace-variable-value for !defined, and add !syntax

svn: r12433

collects/handin-server/checker.ss

@@ -654,9 +654,26 @@
 (define-syntax-rule (!defined id ...)
   ;; expected to be used only with identifiers
   (begin (with-handlers ([exn:fail:contract:variable?
+                          (lambda (_)
+                            (error* "missing binding: ~e" (->disp 'id)))]
+                         [exn:fail:syntax?
+                          (lambda (_)
+                            (error* "bound to a syntax, expecting a value: ~e"
+                                    (->disp 'id)))])
+           (namespace-variable-value `id #t #f
+                                     (get-namespace (submission-eval))))
+         ...))
+
+(provide !syntax)
+(define-syntax-rule (!syntax id ...)
+  ;; expected to be used only with identifiers
+  (begin (with-handlers ([exn:fail:syntax? void]
+                         [exn:fail:contract:variable?
                           (lambda (_)
                             (error* "missing binding: ~e" (->disp 'id)))])
-           ((submission-eval) `id))
+           (namespace-variable-value `id #t #f
+                                     (get-namespace (submission-eval)))
+           (error* "bound to a value, expecting a syntax: ~e" (->disp 'id)))
          ...))
 
 (provide !procedure* !procedure)

collects/handin-server/scribblings/checker.scrbl

@@ -333,6 +333,10 @@ code.}
 
   Checks that @scheme[id] is defined, and is bound to a procedure.}
 
+@defform[(!syntax id arity)]{
+
+  Checks that @scheme[id] is defined, and is bound as a macro.}
+
 @defform[(!procedure* expr arity)]{
 
   Similar to @scheme[!procedure] but omits the defined check, making