diff --git a/src/commands/eval/executor.rs b/src/commands/eval/executor.rs
index 1e0a0ea..6467d03 100644
--- a/src/commands/eval/executor.rs
+++ b/src/commands/eval/executor.rs
@@ -90,6 +90,13 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x.powf(y))),
                 _ => Err(RuntimeError::NoOverloadForTypes),
             },
+            ParseTree::Mod(x, y) => match (self.exec(*x, locals, in_function)?, self.exec(*y, locals, in_function)?) {
+                (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x % y)),
+                (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x % y as f64)),
+                (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 % y)),
+                (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x % y)),
+                _ => Err(RuntimeError::NoOverloadForTypes),
+            },
             ParseTree::EqualTo(x, y) => match (self.exec(*x, locals, in_function)?, self.exec(*y, locals, in_function)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Bool(x == y)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Bool(x as f64 == y)),
@@ -257,3 +264,11 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Iterator for Executor<I>
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn recursion() {
+        let program = ": countdown i ?? <= i i 0 countdown - i 1";
+    }
+}
\ No newline at end of file
diff --git a/src/commands/eval/parser.rs b/src/commands/eval/parser.rs
index 385eb8e..efa2b76 100644
--- a/src/commands/eval/parser.rs
+++ b/src/commands/eval/parser.rs
@@ -41,6 +41,7 @@ pub enum ParseTree {
     Mul(Box<ParseTree>, Box<ParseTree>),
     Div(Box<ParseTree>, Box<ParseTree>),
     Exp(Box<ParseTree>, Box<ParseTree>),
+    Mod(Box<ParseTree>, Box<ParseTree>),
 
     // Boolean Operations
     EqualTo(Box<ParseTree>, Box<ParseTree>),
@@ -118,6 +119,10 @@ impl ParseTree {
                                 Box::new(ParseTree::parse(tokens, globals, locals)?),
                                 Box::new(ParseTree::parse(tokens, globals, locals)?)
                             )),
+                            Op::Mod => Ok(ParseTree::Mod(
+                                Box::new(ParseTree::parse(tokens, globals, locals)?),
+                                Box::new(ParseTree::parse(tokens, globals, locals)?)
+                            )),
                             Op::Equ | Op::LazyEqu | Op::GlobalEqu | Op::LazyGlobalEqu => {
                                 let token = tokens.next()
                                     .ok_or(ParseError::UnexpectedEndInput)?
diff --git a/src/commands/eval/tokenizer.rs b/src/commands/eval/tokenizer.rs
index 28c1a21..20fe8a8 100644
--- a/src/commands/eval/tokenizer.rs
+++ b/src/commands/eval/tokenizer.rs
@@ -40,6 +40,7 @@ pub enum Op {
     Div,
     Exp,
     Equ,
+    Mod,
     LazyEqu,
     GlobalEqu,
     LazyGlobalEqu,
@@ -90,8 +91,9 @@ impl Token {
             "+"  => Ok(Token::Operator(Op::Add)),
             "-"  => Ok(Token::Operator(Op::Sub)),
             "*"  => Ok(Token::Operator(Op::Mul)),
-            "**" => Ok(Token::Operator(Op::Exp)),
             "/"  => Ok(Token::Operator(Op::Div)),
+            "**" => Ok(Token::Operator(Op::Exp)),
+            "%" => Ok(Token::Operator(Op::Mod)),
             "="  => Ok(Token::Operator(Op::Equ)),
             "."  => Ok(Token::Operator(Op::LazyEqu)),
             "=>" => Ok(Token::Operator(Op::GlobalEqu)),
@@ -170,8 +172,8 @@ impl<R: BufRead> std::iter::Iterator for Tokenizer<R> {
         let mut input = String::new();
 
         match self.reader.read_to_string(&mut input) {
-            Ok(0) => return None,
-            Err(e) => return Some(Err(TokenizeError::IO(e))),
+            Ok(0) => None,
+            Err(e) => Some(Err(TokenizeError::IO(e))),
             _ => {
                 let re = regex::Regex::new(r#"[a-zA-Z0-9\.'_]+|[`~!@#\$%\^&\*\(\)\+-=\[\]\{\}\\|;:,<\.>/\?]+|("[^"]+")"#).expect("This wont fail promise :3");