diff --git a/examples/reid/easiest.reid b/examples/reid/easiest.reid
index dce07b9..fa6f89b 100644
--- a/examples/reid/easiest.reid
+++ b/examples/reid/easiest.reid
@@ -2,14 +2,19 @@
 
 import std::print;
 
-fn somethingelse() {
-    return 12;
-}
-
 fn main() {
     let hello = 32 + {
-        2 + somethingelse()
+        2 + 2
     };
-    let beep = hello + 5;
+    let beep = hello + fibonacci(15);
     return beep;
+}
+
+// Fibonacci
+
+fn fibonacci(value: i32) -> i32 {
+    if value < 3 {
+        return 1;
+    }
+    return fibonacci(value - 1) + fibonacci(value - 2);
 }
\ No newline at end of file
diff --git a/src/ast.rs b/src/ast.rs
index f7a6c6b..431bdad 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -10,6 +10,24 @@ where
     fn parse(stream: TokenStream) -> Result<Self, Error>;
 }
 
+#[derive(Debug, Clone)]
+pub enum Type {
+    I32,
+}
+
+impl Parse for Type {
+    fn parse(mut stream: TokenStream) -> Result<Self, Error> {
+        if let Some(Token::Identifier(ident)) = stream.next() {
+            Ok(match &*ident {
+                "i32" => Type::I32,
+                _ => panic!("asd"),
+            })
+        } else {
+            Err(stream.expected_err("type identifier")?)
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub enum Literal {
     I32(i32),
@@ -187,14 +205,34 @@ impl Parse for FunctionDefinition {
 #[derive(Debug, Clone)]
 pub struct FunctionSignature {
     pub name: String,
+    pub args: Vec<(String, Type)>,
+    pub return_type: Option<Type>,
 }
 
 impl Parse for FunctionSignature {
     fn parse(mut stream: TokenStream) -> Result<Self, Error> {
         if let Some(Token::Identifier(name)) = stream.next() {
             stream.expect(Token::ParenOpen)?;
+            let mut args = Vec::new();
+
+            while let Some(Token::Identifier(arg_name)) = stream.peek() {
+                stream.next();
+                stream.expect(Token::Colon)?;
+                args.push((arg_name, stream.parse()?));
+            }
+
             stream.expect(Token::ParenClose)?;
-            Ok(FunctionSignature { name })
+
+            let mut return_type = None;
+            if stream.expect(Token::Arrow).is_ok() {
+                return_type = Some(stream.parse()?);
+            }
+
+            Ok(FunctionSignature {
+                name,
+                args,
+                return_type,
+            })
         } else {
             Err(stream.expected_err("identifier")?)?
         }
diff --git a/src/lexer.rs b/src/lexer.rs
index cd53fef..9624678 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -18,6 +18,8 @@ pub enum Token {
     ReturnKeyword,
     /// `fn`
     FnKeyword,
+    /// `->`
+    Arrow,
 
     // Symbols
     /// `;`
@@ -30,6 +32,12 @@ pub enum Token {
     Plus,
     /// `*`
     Times,
+    /// `-`
+    Minus,
+    /// `>`
+    GreaterThan,
+    /// `<`
+    LessThan,
     /// `(`
     ParenOpen,
     /// `)`
@@ -48,6 +56,7 @@ impl Token {
     pub fn get_token_prec(&self) -> i8 {
         match &self {
             Token::Plus => 10,
+            Token::Minus => 10,
             Token::Times => 20,
             _ => -1,
         }
@@ -160,12 +169,19 @@ pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<FullToken>, Error
                 }
                 Token::DecimalValue(value)
             }
+            '-' if cursor.first() == Some('>') => {
+                cursor.next(); // Eat `>`
+                Token::Arrow
+            }
             // Single character tokens
             '=' => Token::Equals,
             ';' => Token::Semi,
             ':' => Token::Colon,
             '+' => Token::Plus,
             '*' => Token::Times,
+            '-' => Token::Minus,
+            '>' => Token::GreaterThan,
+            '<' => Token::LessThan,
             '(' => Token::ParenOpen,
             ')' => Token::ParenClose,
             '{' => Token::BraceOpen,