Added REPL

src/main.rs

@@ -2,8 +2,11 @@
 extern crate lazy_static;
 
 mod lexer;
+mod repl;
 
-fn main() {}
+fn main() {
+    repl::init();
+}
 
 #[cfg(test)]
 mod tests {

src/repl/mod.rs

@@ -0,0 +1,27 @@
+use crate::lexer::Lexer;
+use std::io::{self, BufRead, Write};
+
+const PROMPT: &'static str = ">> ";
+
+pub fn init() {
+    let stdin = io::stdin();
+    let read_handle = stdin.lock();
+    let stdout = io::stdout();
+    let write_handle = stdout.lock();
+
+    start(read_handle, write_handle);
+}
+
+fn start<R: BufRead, W: Write>(mut ip: R, mut out: W) {
+    loop {
+        out.write_fmt(format_args!("{}", PROMPT)).unwrap();
+        out.flush().unwrap();
+        let mut s = String::new();
+        ip.read_line(&mut s).unwrap();
+        let tokens = Lexer::new(&s);
+
+        for token in tokens {
+            println!("{:?}", token);
+        }
+    }
+}