import Ostap;
import Expr;
import Fun;
import List;

local a   = token ("a") @ lift(fun (a) {if a then "a" else "b" fi}),
      eq  = [token ("="), fun (l, r) {fun (a) {Eq  (l (a), r (a))}}], 
      add = [token ("+"), fun (l, r) {fun (a) {Add (l (a), r (a))}}],
      sub = [token ("-"), fun (l, r) {fun (a) {Sub (l (a), r (a))}}],
      mul = [token ("*"), fun (l, r) {fun (a) {Mul (l (a), r (a))}}],
      div = [token ("/"), fun (l, r) {fun (a) {Div (l (a), r (a))}}],      
      exp = expr ({[Nona, singleton (eq)], [Right, {add, sub}], [Left, {mul, div}]}, a) (id);

fun unpack (x, y) {
  case x of
    Fail (_) -> x
  | Succ (z) -> Succ (z (y))
  esac
}

printf ("%s\n", unpack (parseString (exp |> bypass (eof), "a=a"), true).string);
printf ("%s\n", unpack (parseString (exp |> bypass (eof), "a=a"), false).string); 

printf ("%s\n", unpack (parseString (exp |> bypass (eof), "a*a=a*a"), true).string);
printf ("%s\n", unpack (parseString (exp |> bypass (eof), "a*a=a*a"), false).string);

printf ("%s\n", unpack (parseString (exp |> bypass (eof), "a*a+a/a-a*a=a*a-a"), true).string);
printf ("%s\n", unpack (parseString (exp |> bypass (eof), "a*a+a/a-a*a=a*a-a"), false).string)