cond has an else clause now

2019-05-03 19:36:32 +02:00
parent a1fccd29de
commit 311af423df
2 changed files with 16 additions and 11 deletions
@@ -46,10 +46,15 @@
  (define (rec clauses)
    (if (= nil clauses)
        nil
-      (list 'if (first (first clauses))
-            (pair 'prog (rest (first clauses)))
-            (rec (rest clauses)))))
-  (rec clauses))
+      (if (= (first (first clauses)) 'else)
+          (prog
+           (if (not (= () (rest clauses)))
+               (error "There are additional clauses after the else clause!")
+             (pair 'prog (rest (first clauses)))))
+        (list 'if (first (first clauses))
+              (pair 'prog (rest (first clauses)))
+              (rec (rest clauses))))))
+    (rec clauses))

 (define (nil? x)
  "Checks if the argument is nil."