diff --git a/src/environment.rs b/src/environment.rs
index f9bf56a..f6cd58b 100644
--- a/src/environment.rs
+++ b/src/environment.rs
@@ -1,5 +1,5 @@
-use crate::parser::Datum;
 use crate::parser::make_symbol;
+use crate::parser::Datum;
 use crate::primitives;
 use std::mem;
 
@@ -8,10 +8,12 @@ type Frame = Vec<Mapping>;
 pub type Env = Vec<Frame>;
 
 pub fn get_global_environment() -> Env {
-    vec![vec![(make_symbol("+"), Datum::Procedure(primitives::add)),
-              (make_symbol("*"), Datum::Procedure(primitives::mul)),
-              (make_symbol("-"), Datum::Procedure(primitives::sub)),
-              (make_symbol("="), Datum::Procedure(primitives::eq))]]
+    vec![vec![
+        (make_symbol("+"), Datum::Procedure(primitives::add)),
+        (make_symbol("*"), Datum::Procedure(primitives::mul)),
+        (make_symbol("-"), Datum::Procedure(primitives::sub)),
+        (make_symbol("="), Datum::Procedure(primitives::eq)),
+    ]]
 }
 
 pub fn lookup_variable_value(var: &Datum, env: &Env) -> Datum {
@@ -79,4 +81,4 @@ pub fn extend_environment(vars: Datum, vals: Datum, env: &mut Env) -> Datum {
 pub fn shrink_environment(env: &mut Env) -> Datum {
     env.pop();
     Datum::Unspecified
-}
\ No newline at end of file
+}
diff --git a/src/interpreter.rs b/src/interpreter.rs
index 1ea2d00..b5d3fa6 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -1,9 +1,9 @@
-use crate::parser::Datum;
-use crate::parser::Datum::*;
-use crate::parser::make_symbol;
 use crate::environment;
 use crate::environment::Env;
- 
+use crate::parser::make_symbol;
+use crate::parser::Datum;
+use crate::parser::Datum::*;
+
 fn is_true(exp: &Datum) -> bool {
     match exp {
         Boolean(b) => *b,
@@ -16,7 +16,7 @@ fn is_true(exp: &Datum) -> bool {
 fn has_tag(vec: &Vec<Datum>, tag: &str) -> bool {
     if vec.len() == 0 {
         return false;
-    } 
+    }
     if let Symbol(s) = &vec[0] {
         if s == tag {
             return true;
@@ -49,7 +49,7 @@ fn interpret_define(args: &Vec<Datum>, env: &mut Env) -> Datum {
             let var = &args[1];
             let val = interpret(&args[2], env);
             environment::define_variable(var, val, env)
-        },
+        }
         List(v) => {
             // procedure definition
             let definition_var = &v[0];
@@ -65,8 +65,8 @@ fn interpret_define(args: &Vec<Datum>, env: &mut Env) -> Datum {
             let lambda_body = Datum::List(args[2..].to_vec());
             let lambda = Datum::List(vec![make_symbol("lambda"), lambda_parameters, lambda_body]);
             environment::define_variable(definition_var, lambda, env)
-        },
-        _ => panic!("INTERPRET-DEFINE -- cannot define {:?}", args)
+        }
+        _ => panic!("INTERPRET-DEFINE -- cannot define {:?}", args),
     }
 }
 
@@ -106,8 +106,8 @@ fn interpret_application(vec: &Vec<Datum>, env: &mut Env) -> Datum {
             }
             environment::shrink_environment(env);
             r
-        },
-        _ => panic!("INTERPRET-APPLICATION -- not-aplicable {:?}", args[0])
+        }
+        _ => panic!("INTERPRET-APPLICATION -- not-aplicable {:?}", args[0]),
     }
 }
 
diff --git a/src/main.rs b/src/main.rs
index 540d63b..b7bfac8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,16 +1,46 @@
+mod environment;
 mod interpreter;
 mod lexer;
 mod parser;
 mod primitives;
-mod environment;
+use std::io;
+use std::io::prelude::*;
 
-fn main() {
-    // let scm_code = "(if (= 1 1) (+ 1 1) (* 2 3 4))";
-    // let scm_code = "(begin (define a (+ 2 2)) (* 3 2) (* a a a))";
-    let scm_code = "(begin (define (f n) (if (= n 1) 1 (* n (f (- n 1))))) (f 10))";
+fn repl() {
+    let mut env = environment::get_global_environment();
+    loop {
+        let mut input = String::new();
+        print!(" ]=> ");
+        io::stdout().flush().ok().expect("Could not flush stdout");
+        match io::stdin().read_line(&mut input) {
+            Ok(_) => {
+                let tokens = lexer::read(&input);
+                let datum = parser::parse(tokens);
+                let result = interpreter::interpret(&datum, &mut env);
+                println!("{:?}", result);
+            }
+            Err(error) => println!("error: {}", error),
+        }
+    }
+}
+
+fn interpret_code(scm_code: &str) {
     let tokens = lexer::read(scm_code);
     let datum = parser::parse(tokens);
     let mut env = environment::get_global_environment();
     let result = interpreter::interpret(&datum, &mut env);
     println!("{:?}", result);
 }
+
+fn interpret_file() {}
+
+fn main() {
+    // let scm_code = "(begin (define (f n) (if (= n 1) 1 (* n (f (- n 1))))) (f 10))";
+    let scm_code = "";
+
+    if scm_code.len() > 0 {
+        interpret_code(scm_code);
+    } else {
+        repl();
+    }
+}
diff --git a/src/primitives.rs b/src/primitives.rs
index 34ed86d..3bd0427 100644
--- a/src/primitives.rs
+++ b/src/primitives.rs
@@ -66,8 +66,12 @@ pub fn eq(args: Vec<Datum>) -> Datum {
         for i in 2..args.len() {
             let current = &args[i];
             match (first, current) {
-                (Boolean(b1), Boolean(b2)) => {return Boolean(b1 == b2);},
-                (Number(n1), Number(n2)) => {return Boolean(n1 == n2);},
+                (Boolean(b1), Boolean(b2)) => {
+                    return Boolean(b1 == b2);
+                }
+                (Number(n1), Number(n2)) => {
+                    return Boolean(n1 == n2);
+                }
                 _ => {
                     println!("{:?} is not equal to {:?}", first, current);
                     return Boolean(false);
@@ -76,4 +80,4 @@ pub fn eq(args: Vec<Datum>) -> Datum {
         }
         Boolean(true)
     }
-}
\ No newline at end of file
+}