diff --git a/src/bin/main.rs b/src/bin/main.rs
index 7a8e0a8..0434e15 100644
--- a/src/bin/main.rs
+++ b/src/bin/main.rs
@@ -51,12 +51,21 @@ fn main() {
     }
 
     loop {
-        // todo: configurable prompt
+        // TODO: configurable prompt
         let readline = rl.readline("λ ");
         match readline {
             Ok(line) => {
                 rl.add_history_entry(line.as_str());
-                match lex(line.as_str().to_owned()) {
+                let mut l = line.as_str().to_owned();
+                if !l.starts_with("(") {
+                    l = "(".to_owned() + &l;
+                }
+
+                if !l.ends_with(")") {
+                    l = l + ")";
+                }
+
+                match lex(l) {
                     Ok(a) => {
                         match eval(a.clone(), vt.clone(), ft.clone(), false) {
                             Ok(a) => {