add execute

src/err.rs

@@ -5,3 +5,15 @@ pub enum ParseError {
     #[error(display = "error syntax: {:?}", _0)]
     ErrorSyntax(String),
 }
+
+#[derive(Debug, Error)]
+pub enum RuntimeError {
+    #[error(display = "error vm state: {:?}", _0)]
+    ErrorVmState(String),
+
+    #[error(display = "end vm")]
+    EndVm,
+
+    #[error(display = "not implemented: {:?}", _0)]
+    NotImplemented(String),
+}