refactor: Syntax with unit tests

lib/syntax/Expressions.ml

@@ -0,0 +1,21 @@
+open Literals
+open UnaryOperators
+open BinaryOperators
+
+type expressions =
+  | Literal of literals
+  | UnaryExpression of unary_operators * expressions
+  | BinaryExpression of binary_operators * expressions * expressions
+
+let rec pp_expressions = function
+  | Literal l ->
+      let pp_l = pp_literals l in
+      Printf.sprintf "Literal(%s)" pp_l
+  | 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
+  | BinaryExpression (op, e1, e2) ->
+      let pp_op = pp_binary_operators op
+      and pp_e1 = pp_expressions e1
+      and pp_e2 = pp_expressions e2 in
+      Printf.sprintf "BinaryExpression(%s, %s, %s)" pp_op pp_e1 pp_e2