From b126303628f4b1870094949558f89e587b044c97 Mon Sep 17 00:00:00 2001
From: Jay McCarthy <jay@racket-lang.org>
Date: Sat, 26 Jun 2010 13:08:10 -0600
Subject: [PATCH] Protecting :- outside clauses

---
 collects/datalog/sexp/lang.rkt | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/collects/datalog/sexp/lang.rkt b/collects/datalog/sexp/lang.rkt
index 5aca47af6a..e85e850eb3 100644
--- a/collects/datalog/sexp/lang.rkt
+++ b/collects/datalog/sexp/lang.rkt
@@ -4,6 +4,9 @@
          "../eval.rkt"
          "../ast.rkt")
 
+(define-syntax (:- stx)
+  (raise-syntax-error ':- "only allowed inside ! and ~" stx))
+
 (define-syntax-parameter top
   (λ (stx) (raise-syntax-error '#%top "undefined identifier" stx)))
 (define-syntax-parameter unquote
@@ -48,20 +51,14 @@
 
 (define-syntax (->simple-clause stx)
   (syntax-case stx (:-)
-    [(_ (:- . r))
+    [(_ (:- head body ...))
      (quasisyntax/loc stx
-       (:- . r))]
+       (clause #'#,stx (->literal head) 
+               (list (->literal body) ...)))]
     [(_ e)
      (quasisyntax/loc stx
        (clause #'#,stx (->literal e) empty))]))
 
-(define-syntax (:- stx)
-  (syntax-case stx ()
-    [(_ head body ...)
-     (quasisyntax/loc stx
-       (clause #'#,stx (->literal head) 
-               (list (->literal body) ...)))]))
-
 (define-syntax-rule (define-paren-stx op struct)
   (define-syntax (op stx)
     (syntax-case stx ()