implement chapter 12 in rust

rust/rox/src/function.rs

@@ -1,6 +1,7 @@
 use crate::{
     callable::{Callable, CallingError},
     environment::Environment,
+    instance::Instance,
     interpreter::Interpreter,
     statement::Statement,
     token::Token,
@@ -13,6 +14,7 @@ use std::{cell::RefCell, fmt::Display, rc::Rc};
 #[derive(Debug, Clone)]
 pub struct Function {
     pub name: Token,
+    pub is_initializer: bool,
     pub params: Vec<Token>,
     pub body: Vec<Statement>,
     pub closure: Rc<RefCell<Environment>>,
@@ -52,10 +54,24 @@ impl Callable for Function {
             env.define(param.lexeme.clone(), arg);
         }
 
-        let result = interpreter
+        Ok(interpreter
             .block(&self.body, env)
             .map_err(|e| CallingError::CallInterpretationFailed(e.to_string()))?
-            .unwrap_or(Value::Nil);
-        Ok(result)
+            .unwrap_or(Value::Nil))
+    }
+}
+
+impl Function {
+    pub fn bind(&self, instance: Rc<RefCell<Instance>>) -> Self {
+        let mut env = Environment::with_enclosing(self.closure.clone());
+        env.define("this".to_string(), Value::Instance(instance));
+
+        Self {
+            name: self.name.clone(),
+            is_initializer: self.is_initializer,
+            params: self.params.clone(),
+            body: self.body.clone(),
+            closure: Rc::new(RefCell::new(env)),
+        }
     }
 }