refactor: Syntax with unit tests

lib/syntax/Literals.ml

@@ -0,0 +1,15 @@
+type literals =
+  | Integer of int
+  | Float of float
+  | Character of char
+  | String of string
+  | Boolean of bool
+  | Null
+
+let pp_literals = function
+  | Integer i -> Printf.sprintf "Integer(%d)" i
+  | Float f -> Printf.sprintf "Float(%f)" f
+  | Character c -> Printf.sprintf "Character('%c')" c
+  | String s -> Printf.sprintf "String(\"%s\")" s
+  | Boolean b -> Printf.sprintf "Boolean(%b)" b
+  | Null -> "Null"