import Ostap;
import List;
import Fun;

public fun left (f) {
  fun (c, x) {
     fun (y) {
       f (c (x), y)
     }
  }
}

public fun right (f) {
  fun (c, x) {
    fun (y) {
      c (f (x, y))
    }
  }
}

--- ops -> fun (x, y) {x `op` y}
fun altl (level) {
  case level of
    [assoc, ps] ->
       local assfun = case assoc of Left -> left | Right -> right | Nona -> left esac;
       case map (fun (p) {
                   case p of
                     [op, sema] -> op @ lift(assfun (sema))
                   esac
                 }, ps) of
         p : ps -> foldl (infix |, p, ps)
       esac
  esac
}

public fun expr (ops, opnd) {
  fun inner (ops) {
    case ops of
      {}         -> fun (c) {opnd @ c}
    | level : tl ->
        local lops = altl (level),
              next = inner (tl);

        case level.fst of
          Nona ->
           fun this (c) {
             next (id) |> fun (l) {lops |> fun (op) {next (id) @ fun (r) {c (op)(id, l)(r)}}}
           | next (id) @ c
           }

           this

        | _    ->
           fun this (c) {
             next (id) |> fun (l) {lops |> fun (op) {this (op (c, l))}}
           | next (id) @ c
           }

           this
        esac
    esac  
  }

  inner (ops)
}