Feat: Add Character, String and float literals

lib/syntax/Expressions.ml

@@ -4,6 +4,7 @@ open BinaryOperators
 
 type expressions =
   | Literal of literals
+  | Identifier of string
   | UnaryExpression of unary_operators * expressions
   | BinaryExpression of binary_operators * expressions * expressions
 
@@ -11,6 +12,7 @@ let rec pp_expressions = function
   | Literal l ->
       let pp_l = pp_literals l in
       Printf.sprintf "Literal(%s)" pp_l
+  | Identifier i -> Printf.sprintf "Identifier(\"%s\")" i
   | UnaryExpression (op, e) ->
       let pp_op = pp_unary_operators op and pp_e = pp_expressions e in
       Printf.sprintf "UnaryExpression(%s, %s)" pp_op pp_e