Make environment generic and adapt closures

Added unit test

src/backend/environment.rs

@@ -1,34 +1,45 @@
-use std::collections::HashMap;
-
 use crate::{
-    common::{
-        base_value::BaseValue,
-        lox_result::{runtime_error, LoxResult},
-    },
+    common::lox_result::{runtime_error, LoxResult},
     frontend::source_registry::SourceSlice,
 };
+use std::collections::HashMap;
+use std::fmt::Debug;
 
-#[derive(Debug, Clone, PartialEq)]
-pub struct EnvironmentStack {
-    stack: Vec<HashMap<String, BaseValue>>,
+pub type Environment<T> = HashMap<String, T>;
+
+#[derive(Debug, Clone, PartialEq, Default)]
+pub struct EnvironmentStack<T: Clone + Debug + PartialEq> {
+    stack: Vec<HashMap<String, T>>,
 }
 
-impl EnvironmentStack {
+impl<T: Clone + Debug + PartialEq> EnvironmentStack<T> {
     pub fn new() -> Self {
         EnvironmentStack {
             stack: vec![HashMap::new()],
         }
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.stack.is_empty()
+    }
+
     pub fn push_new_scope(&mut self) {
         self.stack.push(HashMap::new());
     }
 
+    pub fn push_existing_scope(&mut self, scope: HashMap<String, T>) {
+        self.stack.push(scope);
+    }
+
     pub fn pop_scope(&mut self) {
         self.stack.pop();
     }
 
-    pub fn get(&self, name: &str) -> LoxResult<BaseValue> {
+    pub fn clone_last_scope(&mut self) -> HashMap<String, T> {
+        self.stack.last().unwrap().clone()
+    }
+
+    pub fn get(&self, name: &str) -> LoxResult<T> {
         let size = self.stack.len();
 
         for i in (0..size).rev() {
@@ -42,12 +53,12 @@ impl EnvironmentStack {
         )
     }
 
-    pub fn declare(&mut self, name: String, value: BaseValue) -> LoxResult<BaseValue> {
+    pub fn declare(&mut self, name: String, value: T) -> LoxResult<T> {
         self.stack.last_mut().unwrap().insert(name, value.clone());
         Ok(value)
     }
 
-    pub fn set(&mut self, name: String, value: BaseValue) -> LoxResult<BaseValue> {
+    pub fn set(&mut self, name: String, value: T) -> LoxResult<T> {
         let size = self.stack.len();
 
         for i in (0..size).rev() {
@@ -69,3 +80,90 @@ impl EnvironmentStack {
         )
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn declare_and_get() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        assert_eq!(env.get("a").unwrap(), 1);
+    }
+
+    #[test]
+    fn get_undefined_is_error() {
+        let env: EnvironmentStack<i32> = EnvironmentStack::new();
+        assert!(env.get("nope").is_err());
+    }
+
+    #[test]
+    fn declare_overwrites_in_same_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.declare("a".to_string(), 2).unwrap();
+        assert_eq!(env.get("a").unwrap(), 2);
+    }
+
+    #[test]
+    fn inner_scope_shadows_outer_and_unshadows_on_pop() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.push_new_scope();
+        env.declare("a".to_string(), 2).unwrap();
+        assert_eq!(env.get("a").unwrap(), 2);
+        env.pop_scope();
+        assert_eq!(env.get("a").unwrap(), 1);
+    }
+
+    #[test]
+    fn get_falls_through_to_outer_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.push_new_scope();
+        assert_eq!(env.get("a").unwrap(), 1);
+    }
+
+    #[test]
+    fn set_updates_existing_value_in_outer_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.push_new_scope();
+        env.set("a".to_string(), 9).unwrap();
+        env.pop_scope();
+        assert_eq!(env.get("a").unwrap(), 9);
+    }
+
+    #[test]
+    fn set_undefined_is_error() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        assert!(env.set("a".to_string(), 1).is_err());
+    }
+
+    #[test]
+    fn pop_scope_discards_inner_declarations() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.push_new_scope();
+        env.declare("temp".to_string(), 5).unwrap();
+        env.pop_scope();
+        assert!(env.get("temp").is_err());
+    }
+
+    #[test]
+    fn push_existing_scope_makes_values_visible() {
+        let mut scope = HashMap::new();
+        scope.insert("k".to_string(), 7);
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.push_existing_scope(scope);
+        assert_eq!(env.get("k").unwrap(), 7);
+    }
+
+    #[test]
+    fn clone_last_scope_returns_top_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        let scope = env.clone_last_scope();
+        assert_eq!(scope.get("a"), Some(&1));
+    }
+}