move Expr out of parser

src/main.rs

@@ -1,6 +1,7 @@
 use std::{fs::File, io::Read};
 
 mod token;
+mod expr;
 mod lexer;
 use lexer::Lexer;
 mod parser;
@@ -30,7 +31,7 @@ fn main() -> std::io::Result<()> {
     loop {
         let parsed = parser.parse();
         match parsed {
-            parser::Expr::EOL => break,
+            expr::Expr::EOL => break,
             _ => {
                 println!("AST:   {:?}", parsed);
                 let eval = Evaluator::new(parsed);