Full code coverage

A1/infix-ae.rkt

@@ -1,5 +1,7 @@
 #lang plait
 
+(define minutes-spent 60)
+
 #| BNF for the AE language:
    ae: NUMBER
        | { ae + ae }
@@ -40,7 +42,12 @@
     [(Add l r) (+ (eval l) (eval r))]
     [(Sub l r) (- (eval l) (eval r))]
     [(Mul l r) (* (eval l) (eval r))]
-    [(Div l r) (/ (eval l) (eval r))]))
+    [(Div l r) (if (equal? 0 (eval r))
+                  (cond
+                    [(< 0 (eval l)) +inf.0]
+                    [(> 0 (eval l)) -inf.0]
+                    [else +nan.0])
+                  (/ (eval l) (eval r)))]))
 
 ;; evaluate an AE program contained in an s-expr
 (define (run sx)
@@ -53,4 +60,6 @@
 (test (run `{8 / 2})  4)
 (test (run `{-8 / 0})  -inf.0)
 (test (run `{8 / {5 - 5}})  +inf.0)
-(test (run `{1 / {1 / 0}}) 0.0)
+(test (run `{1 / {1 / 0}}) 0.0)
+(test (run `{0 / 0}) +nan.0) ; Special 0/0 case
+(test/exn (run `{+ 1 1}) "parse") ; Parse error