added list len, front, and back

tests/test_lib_append.rs

@@ -85,4 +85,106 @@ mod append_lib_tests {
             result.to_string(),
         );
     }
+
+    #[test]
+    fn test_len_empty() {
+        let document = "(len ())";
+        let result = "0";
+
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms).unwrap();
+        dynamic_stdlib(&mut syms).unwrap();
+
+        assert_eq!(
+            *eval(&lex(&document.to_string()).unwrap(), &mut syms)
+                .unwrap()
+                .to_string(),
+            result.to_string(),
+        );
+    }
+
+    #[test]
+    fn test_len_normal() {
+        let document = "(len (1 2 3))";
+        let result = "3";
+
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms).unwrap();
+        dynamic_stdlib(&mut syms).unwrap();
+
+        assert_eq!(
+            *eval(&lex(&document.to_string()).unwrap(), &mut syms)
+                .unwrap()
+                .to_string(),
+            result.to_string(),
+        );
+    }
+
+    #[test]
+    fn test_car_empty() {
+        let document = "(car ())";
+
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms).unwrap();
+        dynamic_stdlib(&mut syms).unwrap();
+
+        assert_eq!(
+            *eval(&lex(&document.to_string()).unwrap(), &mut syms)
+                .err()
+                .unwrap()
+                .to_string(),
+            "error in call to car: argument is empty".to_string(),
+        );
+    }
+
+    #[test]
+    fn test_car_normal() {
+        let document = "(car (1 2 3))";
+        let result = "1";
+
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms).unwrap();
+        dynamic_stdlib(&mut syms).unwrap();
+
+        assert_eq!(
+            *eval(&lex(&document.to_string()).unwrap(), &mut syms)
+                .unwrap()
+                .to_string(),
+            result.to_string(),
+        );
+    }
+
+    #[test]
+    fn test_cdr_empty() {
+        let document = "(cdr ())";
+
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms).unwrap();
+        dynamic_stdlib(&mut syms).unwrap();
+
+        assert_eq!(
+            *eval(&lex(&document.to_string()).unwrap(), &mut syms)
+                .err()
+                .unwrap()
+                .to_string(),
+            "error in call to cdr: argument is empty".to_string(),
+        );
+    }
+
+    #[test]
+    fn test_cdr_normal() {
+        let document = "(cdr (1 2 3))";
+        let result = "3";
+
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms).unwrap();
+        dynamic_stdlib(&mut syms).unwrap();
+
+        assert_eq!(
+            *eval(&lex(&document.to_string()).unwrap(), &mut syms)
+                .unwrap()
+                .to_string(),
+            result.to_string(),
+        );
+    }
 }