From 14d6b476bdcd909f99749ebc231cc0e38d121efd Mon Sep 17 00:00:00 2001
From: Enrico Lumetti <enrico.lumetti@gmail.com>
Date: Wed, 10 Aug 2022 23:28:09 +0200
Subject: [PATCH] Fix subtraction, convert tests to rackunit

---
 rint.rkt      | 1 +
 test-rint.rkt | 9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/rint.rkt b/rint.rkt
index d91bdaf..8ebd440 100644
--- a/rint.rkt
+++ b/rint.rkt
@@ -21,6 +21,7 @@
     [(Int n) n]
     [(Prim 'read '()) (read-fixnum)]
     [(Prim '- (list e)) (fx- 0 (interp-exp e))]
+    [(Prim '- (list e1 e2)) (fx- (interp-exp e1) (interp-exp e2))]
     [(Prim '+ (list e1 e2)) (fx+ (interp-exp e1) (interp-exp e2))]))
 
 (define (interp-RInt p)
diff --git a/test-rint.rkt b/test-rint.rkt
index 94e8a1b..794fe73 100644
--- a/test-rint.rkt
+++ b/test-rint.rkt
@@ -15,11 +15,16 @@
 (define test-rint-tests
  (test-suite
   "RInt interpretation tests"
-  (test-case 
+  (test-case
    "program with input"
    (check-equal?
     -5
     (with-input-from-num-list '(3)
-       (lambda () (interp-RInt program)))))))
+       (lambda () (interp-RInt program)))))
+  (test-case 
+   "simple difference"
+   (check-equal?
+    -3
+    (interp-RInt (Program '() (Prim '- (list (Int 5) (Int 8)))))))))