Include environment when evaluating

rust/src/evaluator.rs

@@ -1,16 +1,37 @@
 use std::ops;
+use std::collections::HashMap;
 
 use crate::parser;
 use parser::Atom;
 
-pub fn eval(ast: &parser::Expr) -> parser::Atom {
+pub struct Env<'a> {
+    pub parent: Option<&'a Env<'a>>,
+    pub values: HashMap<String, Atom>
+}
+
+impl<'a> Env<'a> {
+    pub fn global() -> Self {
+        Env {
+            parent: None,
+            values: HashMap::new(),
+        }
+    }
+    pub fn child(parent: &'a Env<'a>) -> Self {
+        Env {
+            parent: Some(parent),
+            values: HashMap::new(),
+        }
+    }
+}
+
+pub fn eval(ast: &parser::Expr, env: &mut Env) -> parser::Atom {
     match ast {
         parser::Expr::Atom(a) => a.clone(),
-        parser::Expr::UnaryMinus(a) => -eval(&a),
-        parser::Expr::Plus(a, b) => eval(&a) + eval(&b),
-        parser::Expr::Minus(a, b) => eval(&a) - eval(&b),
-        parser::Expr::Mult(a, b) => eval(&a) * eval(&b),
-        parser::Expr::Div(a, b) => eval(&a) / eval(&b),
+        parser::Expr::UnaryMinus(a) => -eval(&a, env),
+        parser::Expr::Plus(a, b) => eval(&a, env) + eval(&b, env),
+        parser::Expr::Minus(a, b) => eval(&a, env) - eval(&b, env),
+        parser::Expr::Mult(a, b) => eval(&a, env) * eval(&b, env),
+        parser::Expr::Div(a, b) => eval(&a, env) / eval(&b, env),
         _ => panic!("Couldn't evalute expression {{ {:?} }}", ast),
     }
 }

rust/src/main.rs

@@ -18,6 +18,7 @@ struct Cli {
 }
 
 fn repl(cli: &Cli) {
+    let mut global = evaluator::Env::global();
     loop {
         let mut line = String::new();
         io::stdin().read_line(&mut line).unwrap();
@@ -27,7 +28,7 @@ fn repl(cli: &Cli) {
         } else {
             match &tree {
                 parser::Stmt::ReplPrint(expr) =>
-                    println!("{}", evaluator::eval(expr)),
+                    println!("{}", evaluator::eval(expr, &mut global)),
                 _ => todo!(),
             }
         }