better error message for R5RS transformer expressions that are not 'syntax-rules'

svn: r14183

collects/r5rs/main.ss

@@ -1,10 +1,14 @@
 
 (module main scheme/base
   (require scheme/mpair
-           (for-syntax scheme/base syntax/kerncase)
+           (for-syntax scheme/base syntax/kerncase
+                       "private/r5rs-trans.ss")
            (only-in mzscheme transcript-on transcript-off))
 
-  (provide (for-syntax syntax-rules ...)
+  (provide (for-syntax syntax-rules ...
+                       (rename-out [syntax-rules-only #%top]
+                                   [syntax-rules-only #%app]
+                                   [syntax-rules-only #%datum]))
            (rename-out
             [mcons cons]
             [mcar car]

collects/r5rs/private/r5rs-trans.ss

@@ -0,0 +1,11 @@
+#lang scheme/base
+(require (for-syntax scheme/base))
+(provide syntax-rules-only)
+
+(define-syntax (syntax-rules-only stx)
+  (syntax-case stx ()
+    [(_ . form)
+     (raise-syntax-error
+      'macro-transformer
+      "only a `syntax-rules' form is allowed"
+      #'form)]))

collects/r5rs/r5rs.scrbl

@@ -1,6 +1,7 @@
 #lang scribble/doc
 @(require scribble/manual
-          (for-label r5rs
+          (for-label (only-meta-in 0 r5rs)
+                     (only-in r5rs syntax-rules ...)
                      (only-in mzscheme #%plain-module-begin)
                      (only-in scheme/mpair mmap)
                      (only-in scheme/contract one-of/c)