open List
open Genlex
open Str
open String
open Char

type vname = string 
type term = V of vname | T of (string * (term list))
type subst = (vname*term) list



let maiuscula s = let v = s.[0] in ((code v >= code 'A') && (code v <= code 'Z'))

let trata s e =
  match e with 
      [] -> 
	if maiuscula s then V s
	else T (s,e)
    | _ -> T (s,e)


let lexer = make_lexer ["("; ")"; ","]


(*
E   ::= id F
F   ::= \epsilon
F   ::= (E EL)
EL  ::= ,E EL
EL  ::= \epsilon
*)
let rec parse_expr = parser (* corresponde a entrada E da gramatica *)
[< 'Ident s; e = parse_F>] -> trata s e
and parse_F = parser (* corresponde a entrada E' da gramatica *)
[< 'Kwd "("; e = parse_expr; el = parse_EL; 'Kwd ")" >] -> e::el
| [< >] -> []
and parse_EL = parser (* corresponde a entrada T' da gramatica *)
[< 'Kwd ","; e = parse_expr; el = parse_EL >] -> e::el
| [< >] -> []



let parse_expression = parser [< e = parse_expr; _ = Stream.empty >] -> e;;

(* função principal de leitura usando streams*)
let expression_of_string s = parse_expression(lexer(Stream.of_string s));;

let rec string_of_expression e =
match e with
    V s -> s
  | T (e,el) -> (e^(if el = [] then "" else "("^(aux el)^")"))
and   aux l =
    match l with 
	[] -> ""
      | [e] ->  (string_of_expression e)
      | e::li ->  
	  ( (string_of_expression e)^","^aux li)