diff --git a/examples/ackermann.sb b/examples/ackermann.sb
index 64ffc09..c07a96f 100644
--- a/examples/ackermann.sb
+++ b/examples/ackermann.sb
@@ -4,7 +4,7 @@ fn main() {
     println(ackermann(m, n))
 }
 
-fn ackermann(m, n) {
+fn ackermann(m int, n int) {
     if m == 0 {
         return n + 1
     } else if n == 0 {
diff --git a/examples/fib.sb b/examples/fib.sb
index 683b902..7f7011a 100644
--- a/examples/fib.sb
+++ b/examples/fib.sb
@@ -3,7 +3,7 @@ fn main() {
     println(fib(num))
 }
 
-fn fib(n) { 
+fn fib(n int) { 
     if 1 >= n {
         return n
     }
diff --git a/examples/greeter.sb b/examples/greeter.sb
index c27bb4e..c2597b8 100644
--- a/examples/greeter.sb
+++ b/examples/greeter.sb
@@ -2,6 +2,6 @@ fn main() {
     println(greet("World"))
 }
 
-fn greet(name) {
+fn greet(name string) {
     return "Hello " + name
 }
diff --git a/lib/stdio.sb b/lib/stdio.sb
index d135d76..25fa46e 100644
--- a/lib/stdio.sb
+++ b/lib/stdio.sb
@@ -1,16 +1,16 @@
 // Raw wrapper around _printf builtin function.
 // Writes the given content to stdout
-fn print(msg) {
+fn print(msg string) {
     _printf(msg)
 }
 
 // Like print(), but with an extra newline ('\n') character
-fn println(msg) {
+fn println(msg string) {
     print(msg + "\n")
 }
 
 // Prints the size of an array
-fn len(arr) {
+fn len(arr int[]) {
     let c = 0
     while arr[c] {
         c = c + 1
@@ -21,7 +21,7 @@ fn len(arr) {
 
 // Reverses an array
 // TODO: fix me!
-fn rev(arr) {
+fn rev(arr int[]) {
 
     let l = len(arr)
     let new_arr = []
diff --git a/src/main.rs b/src/main.rs
index 03f0b03..b44b359 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -67,6 +67,7 @@ fn main() -> Result<(), String> {
 
     let tokens = lexer::tokenize(&contents);
     let program = parser::parse(tokens, Some(contents))?;
+    dbg!(&program);
 
     let output = generator::js::JsGenerator::generate(program);
     let mut file = std::fs::File::create(out_file).expect("create failed");
diff --git a/src/parser/node_type.rs b/src/parser/node_type.rs
index fcf1179..507b1d6 100644
--- a/src/parser/node_type.rs
+++ b/src/parser/node_type.rs
@@ -32,6 +32,27 @@ pub struct Function {
 #[derive(Debug, Eq, PartialEq)]
 pub struct Variable {
     pub name: String,
+    pub ty: Option<Type>,
+}
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum Type {
+    Int,
+    Str,
+    Bool,
+    Array(Box<Type>),
+}
+
+impl TryFrom<String> for Type {
+    type Error = String;
+    fn try_from(s: String) -> Result<Self, Self::Error> {
+        match s.as_ref() {
+            "int" => Ok(Self::Int),
+            "string" => Ok(Self::Str),
+            "bool" => Ok(Self::Bool),
+            _ => Err("Expected Type".into()),
+        }
+    }
 }
 
 #[derive(Debug, Eq, PartialEq)]
diff --git a/src/parser/rules.rs b/src/parser/rules.rs
index 3f0998a..4fce8ed 100644
--- a/src/parser/rules.rs
+++ b/src/parser/rules.rs
@@ -58,9 +58,7 @@ impl Parser {
 
         let arguments: Vec<Variable> = match self.peek()? {
             t if t.kind == TokenKind::BraceClose => Vec::new(),
-            _ => self
-                .parse_arguments()
-                .expect("Failed to parse function arguments"),
+            _ => self.parse_arguments()?,
         };
 
         self.match_token(TokenKind::BraceClose)?;
@@ -82,7 +80,10 @@ impl Parser {
                 TokenKind::Comma => {
                     continue;
                 }
-                TokenKind::Identifier(name) => args.push(Variable { name: name }),
+                TokenKind::Identifier(name) => args.push(Variable {
+                    name: name,
+                    ty: Some(self.parse_type()?),
+                }),
                 _ => return Err(self.make_error(TokenKind::Identifier("Argument".into()), next)),
             }
         }
@@ -90,6 +91,21 @@ impl Parser {
         Ok(args)
     }
 
+    fn parse_type(&mut self) -> Result<Type, String> {
+        let next = self.next()?;
+        let typ = match next.kind {
+            TokenKind::Identifier(t) => Type::try_from(t),
+            _ => Err("Expected type".into()),
+        }?;
+        if let Ok(_) = self.peek_token(TokenKind::SquareBraceOpen) {
+            self.drop(1);
+            self.match_token(TokenKind::SquareBraceClose)?;
+            Ok(Type::Array(Box::new(typ)))
+        } else {
+            Ok(typ)
+        }
+    }
+
     fn parse_statement(&mut self) -> Result<Statement, String> {
         let token = self.peek()?;
         let state = match &token.kind {
@@ -333,12 +349,12 @@ impl Parser {
         self.match_keyword(Keyword::Let)?;
         match (self.next()?.kind, self.peek()?.kind) {
             (TokenKind::Identifier(name), TokenKind::SemiColon) => {
-                Ok(Statement::Declare(Variable { name }, None))
+                Ok(Statement::Declare(Variable { name, ty: None }, None))
             }
             (TokenKind::Identifier(name), TokenKind::Assign) => {
                 self.drop(1);
                 let exp = self.parse_expression().ok();
-                Ok(Statement::Declare(Variable { name }, exp))
+                Ok(Statement::Declare(Variable { name, ty: None }, exp))
             }
             other => Err(format!("Expected identifier, found {:?}", other)),
         }
diff --git a/src/parser/tests.rs b/src/parser/tests.rs
index c2b099c..74c0c53 100644
--- a/src/parser/tests.rs
+++ b/src/parser/tests.rs
@@ -120,7 +120,7 @@ fn test_parse_variable_declaration_added() {
 #[test]
 fn test_parse_function_with_args() {
     let raw = "
-    fn main(foo) {
+    fn main(foo int) {
         return foo
     }
     ";
@@ -132,7 +132,7 @@ fn test_parse_function_with_args() {
 #[test]
 fn test_parse_function_call() {
     let raw = "
-    fn main(foo) {
+    fn main(foo int) {
         foo()
     }
 
@@ -184,7 +184,7 @@ fn test_parse_nexted_function_call() {
         fib(fib(2), 2)
     }
 
-    fn fib(n) {
+    fn fib(n int) {
         return 2
     }
     ";
@@ -244,7 +244,7 @@ fn test_parse_compound_ops_with_strings() {
 #[test]
 fn test_parse_compound_ops_with_identifier() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         return 2 * n
     }
     ";
@@ -256,7 +256,7 @@ fn test_parse_compound_ops_with_identifier() {
 #[test]
 fn test_parse_compound_ops_with_identifier_first() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         return n * 2
     }
     ";
@@ -268,7 +268,7 @@ fn test_parse_compound_ops_with_identifier_first() {
 #[test]
 fn test_parse_compound_ops_return() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         return 2 * n
     }
     ";
@@ -280,7 +280,7 @@ fn test_parse_compound_ops_return() {
 #[test]
 fn test_parse_basic_conditional() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         if n {
             return n
         }
@@ -294,7 +294,7 @@ fn test_parse_basic_conditional() {
 #[test]
 fn test_parse_basic_conditional_with_multiple_statements() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         if n {
             let x = 2 * n
             return x
@@ -309,7 +309,7 @@ fn test_parse_basic_conditional_with_multiple_statements() {
 #[test]
 fn test_parse_conditional_else_if_branch() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         if n > 10 {
             let x = 2 * n
             return x
@@ -326,7 +326,7 @@ fn test_parse_conditional_else_if_branch() {
 #[test]
 fn test_parse_conditional_multiple_else_if_branch_branches() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         if n > 10 {
             let x = 2 * n
             return x
@@ -345,7 +345,7 @@ fn test_parse_conditional_multiple_else_if_branch_branches() {
 #[test]
 fn test_parse_conditional_else_branch() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         if n > 10 {
             let x = 2 * n
             return x
@@ -362,7 +362,7 @@ fn test_parse_conditional_else_branch() {
 #[test]
 fn test_parse_conditional_elseif_else_branch() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         if n > 10 {
             let x = 2 * n
             return x
@@ -383,7 +383,7 @@ fn test_parse_conditional_elseif_else_branch() {
 #[test]
 fn test_int_array() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         let arr = [1, 2, 3]
         return arr
     }
@@ -396,7 +396,7 @@ fn test_int_array() {
 #[test]
 fn test_string_array() {
     let raw = "
-    fn main(n) {
+    fn main(n int) {
         return [\"Foo\", \"Bar\", \"Baz\"]
     }
     ";
@@ -533,7 +533,7 @@ fn test_uninitialized_variables() {
 #[test]
 fn test_function_call_math() {
     let raw = "
-    fn main(m) {
+    fn main(m int) {
         main(m - 1)
     }
     ";
@@ -545,7 +545,7 @@ fn test_function_call_math() {
 #[test]
 fn test_function_multiple_args() {
     let raw = "
-    fn main(m, n) {
+    fn main(m int, n int) {
         main(m, n)
     }
     ";