add evaluator

src/eval.rs

@@ -0,0 +1,38 @@
+use crate::parser::{BinaryOp, Expr, UnaryOp};
+
+pub struct Evaluator {
+    ast: Expr
+}
+
+impl Evaluator {
+    pub fn new(ast: Expr) -> Self {
+        Self {
+            ast
+        }
+    }
+
+    fn eval_expr(&self, expr: Expr) -> i64 {
+        match expr {
+            Expr::Number(n) => n,
+            Expr::Unary { op, right } => {
+                match op {
+                    UnaryOp::Neg => -self.eval_expr(*right)
+                }
+            },
+            Expr::Binary { op, left, right } => {
+                match op {
+                    BinaryOp::Add => self.eval_expr(*left) + self.eval_expr(*right),
+                    BinaryOp::Sub => self.eval_expr(*left) - self.eval_expr(*right),
+                    BinaryOp::Mul => self.eval_expr(*left) * self.eval_expr(*right),
+                    BinaryOp::Div => self.eval_expr(*left) / self.eval_expr(*right),
+                    BinaryOp::Mod => self.eval_expr(*left) % self.eval_expr(*right)
+                }
+            },
+            expr => panic!("can't eval expression: {expr:?}")
+        }
+    }
+
+    pub fn eval(&self) -> i64 {
+        self.eval_expr(self.ast.clone())
+    }
+}

src/main.rs

@@ -5,6 +5,8 @@ mod lexer;
 use lexer::Lexer;
 mod parser;
 use parser::Parser;
+mod eval;
+use eval::Evaluator;
 
 fn main() -> std::io::Result<()> {
     let args = std::env::args().collect::<Vec<String>>();
@@ -29,7 +31,11 @@ fn main() -> std::io::Result<()> {
         let parsed = parser.parse();
         match parsed {
             parser::Expr::EOL => break,
-            _ => println!("{:?}", parsed)
+            _ => {
+                println!("AST:   {:?}", parsed);
+                let eval = Evaluator::new(parsed);
+                println!("Eval:  {:?}", eval.eval());
+            }
         }
     }
 

src/parser.rs

@@ -1,6 +1,6 @@
 use crate::token::Token;
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum BinaryOp {
     Add,
     Sub,
@@ -9,7 +9,7 @@ pub enum BinaryOp {
     Mod
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum UnaryOp {
     Neg
 }
@@ -27,7 +27,7 @@ fn infix_bp(op: &BinaryOp) -> (u8, u8) {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum Expr {
     Number(i64),
     Ident(String),