added list len, front, and back

src/stl.rs

@@ -250,6 +250,39 @@ pub fn static_stdlib(syms: &mut SymTable) -> Result<(), String> {
         },
     );
 
+    syms.insert(
+        "len".to_string(),
+        Symbol {
+            name: String::from("len"),
+            args: Args::Strict(vec![Type::Seg]),
+            conditional_branches: false,
+            docs: append::LEN_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(append::len_callback)),
+        },
+    );
+
+    syms.insert(
+        "car".to_string(),
+        Symbol {
+            name: String::from("car"),
+            args: Args::Strict(vec![Type::Seg]),
+            conditional_branches: false,
+            docs: append::CAR_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(append::car_callback)),
+        },
+    );
+
+    syms.insert(
+        "cdr".to_string(),
+        Symbol {
+            name: String::from("cdr"),
+            args: Args::Strict(vec![Type::Seg]),
+            conditional_branches: false,
+            docs: append::CDR_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(append::cdr_callback)),
+        },
+    );
+
     Ok(())
 }