Check for let pattern matches that they have only one sum

[scheme.git] / ast.scm

diff --git a/ast.scm b/ast.scm
index b3f21bd07d6d07ba2b64017cff0a365cbf77abd4..342fe453a4d9276c36237e43e1a7069b5ec75670 100644 (file)
--- 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))