X-Git-Url: http://git.lukelau.me/?p=scheme.git;a=blobdiff_plain;f=ast.scm;fp=ast.scm;h=342fe453a4d9276c36237e43e1a7069b5ec75670;hp=b3f21bd07d6d07ba2b64017cff0a365cbf77abd4;hb=e4dc23d659849c88cec8c7e57d0d463f9493850e;hpb=9fd836fa6cbc686d277684101319f835d55fc5b3

diff --git a/ast.scm b/ast.scm
index b3f21bd..342fe45 100644
--- a/ast.scm
+++ b/ast.scm
@@ -99,10 +99,17 @@
 
 		   [type (data-tor-type data-layouts sum-name)]
 
-		   [sum (assoc sum-name (cdr (assoc type data-layouts)))]
+		   [sums (cdr (assoc type data-layouts))]
+		   [sum (assoc sum-name sums)]
 		   
 		   [expected-number (length (cdr sum))])
 
+					; assert that we only do a let pattern match on an ADT with exactly one sum
+	      (when (not (= 1 (length sums)))
+		(error #f (format "Cannot pattern match a ~a in a let since it has ~a possible constructors"
+				  type
+				  (length sums))))
+
 					; assert that there is the correct number of bindings
 	      (when (not (= (length products)
 			    expected-number))