Be aware of semicolons and commas in List Use @ for concatenation # [1; 2; 3];; - : int list = [1; 2; 3] # 1 :: (2 :: (3 :: []));; - : int list = [1; 2; 3] # 1 :: 2 :: 3 :: [];; - : int list = [1; 2; 3]