copy-paste assignment 2~5

src/assignments/assignment11/peano_nat_grade.rs

@@ -0,0 +1,38 @@
+#[cfg(test)]
+mod test_peano_nat {
+    use crate::assignments::assignment11::peano_nat::*;
+
+    #[test]
+    fn test_from_as_usize() {
+        assert_eq!(Nat::from_usize(0), Nat::O);
+        assert_eq!(
+            Nat::from_usize(2),
+            Nat::S(Box::new(Nat::S(Box::new(Nat::O))))
+        );
+
+        for n in 0..100 {
+            assert_eq!(Nat::from_usize(n).as_usize(), n);
+        }
+    }
+
+    fn safe_sub(i: usize, j: usize) -> usize {
+        if i > j {
+            i - j
+        } else {
+            0
+        }
+    }
+
+    #[test]
+    fn test_add_sub_mul() {
+        for i in 0..30 {
+            let n = Nat::from_usize(i);
+            for j in 0..30 {
+                let m = Nat::from_usize(j);
+                assert_eq!((n.clone() + m.clone()).as_usize(), i + j);
+                assert_eq!((n.clone() - m.clone()).as_usize(), safe_sub(i, j));
+                assert_eq!((n.clone() * m.clone()).as_usize(), i * j);
+            }
+        }
+    }
+}