1 files changed, 63 insertions, 0 deletions
diff --git a/jlox/src/com/craftinginterpreters/lox/Environment.java b/jlox/src/com/craftinginterpreters/lox/Environment.java
new file mode 100644
index 0000000..407b9b3
--- /dev/null
+++ b/jlox/src/com/craftinginterpreters/lox/Environment.java
@@ -0,0 +1,63 @@
+package com.craftinginterpreters.lox;
+
+import java.util.HashMap;
+import java.util.Map;
+
+class Environment {
+    final Environment enclosing;
+    private final Map<String, Object> values = new HashMap<>();
+
+    Environment() {
+        enclosing = null;
+    }
+
+    Environment(Environment enclosing) {
+        this.enclosing = enclosing;
+    }
+
+    Object get(Token name) {
+        if (values.containsKey(name.lexeme)) {
+            return values.get(name.lexeme);
+        }
+
+        if (enclosing != null)
+            return enclosing.get(name);
+
+        throw new RuntimeError(name, "Undefined variable '" + name.lexeme + "'.");
+    }
+
+    void assign(Token name, Object value) {
+        if (values.containsKey(name.lexeme)) {
+            values.put(name.lexeme, value);
+            return;
+        }
+
+        if (enclosing != null) {
+            enclosing.assign(name, value);
+            return;
+        }
+
+        throw new RuntimeError(name, "Undefined variable '" + name.lexeme + "'.");
+    }
+
+    void define(String name, Object value) {
+        values.put(name, value);
+    }
+
+    Environment ancestor(int distance) {
+        Environment environment = this;
+        for (int i = 0; i < distance; i++) {
+            environment = environment.enclosing;
+        }
+
+        return environment;
+    }
+
+    Object getAt(int distance, String name) {
+        return ancestor(distance).values.get(name);
+    }
+
+    void assignAt(int distance, Token name, Object value) {
+        ancestor(distance).values.put(name.lexeme, value);
+    }
+}