diff --git a/schala-lang/language/src/typechecking.rs b/schala-lang/language/src/typechecking.rs
index e900ea7..5f287f3 100644
--- a/schala-lang/language/src/typechecking.rs
+++ b/schala-lang/language/src/typechecking.rs
@@ -16,10 +16,24 @@ struct TypeError { }
 #[derive(Debug, Clone)]
 enum MonoType {
   Var(Rc<String>),
-  Const(Rc<String>),
+  Const(TConst),
   Arrow(Rc<String>)
 }
 
+#[derive(Debug, Clone)]
+enum TConst {
+  User(Rc<String>),
+  Unit,
+  Nat,
+  Int
+}
+
+impl TConst {
+  fn user(name: &str) -> TConst {
+    TConst::User(Rc::new(name.to_string()))
+  }
+}
+
 #[derive(Debug, Clone)]
 struct PolyType {
   vars: Vec<Rc<String>>,
@@ -41,7 +55,7 @@ impl TypeContext {
 
 impl TypeContext {
   fn infer_ast(&mut self, ast: &AST) -> TypeResult<MonoType> {
-    let mut output = MonoType::Const(Rc::new("Unit".to_string()));
+    let mut output = MonoType::Const(TConst::Unit);
     for statement in ast.0.iter() {
       output = match statement {
         Statement::ExpressionStatement(ref expr) => self.infer_expr(expr)?,
@@ -59,14 +73,14 @@ impl TypeContext {
   }
 
   fn infer_decl(&mut self, expr: &Declaration) -> TypeResult<MonoType> {
-    Ok(MonoType::Const(Rc::new("Unimplemented".to_string())))
+    Ok(MonoType::Const(TConst::user("unimplemented")))
   }
 
   fn infer_expr_type(&mut self, expr_type: &ExpressionType) -> TypeResult<MonoType> {
     use self::ExpressionType::*;
     match expr_type {
-      NatLiteral(_) => Ok(MonoType::Const(Rc::new("Nat".to_string()))),
-      _ => Ok(MonoType::Const(Rc::new("Unimplemented".to_string())))
+      NatLiteral(_) => Ok(MonoType::Const(TConst::Nat)),
+      _ => Ok(MonoType::Const(TConst::user("unimplemented")))
     }
   }
 }