bug fixes and performance improvements

src/rule/matcher.rs

@@ -0,0 +1,10 @@
+use std::rc::Rc;
+
+use crate::ast::Expr;
+
+use super::state::State;
+
+pub trait Matcher {
+  fn new(pattern: Rc<Vec<Expr>>) -> Self;
+  fn apply<'a>(&self, source: &'a [Expr]) -> Option<State<'a>>;
+}