Added history (session based)

src/repl.rs

@@ -13,12 +13,14 @@ pub fn repl(ast_print: bool) {
                 // end of the string if stdin is connected to a file
                 // or unsupported terminal; this can interfere with
                 // error printing.
+                rl.add_history_entry(&line);
                 let line = line.trim_end();
 
                 if line == "exit" {
                     println!("bye");
                     break;
                 }
+                
                 let mut parser = Parser::new(&line);
                 let value = parser.init().and_then(|ast| {
                     if ast_print {