src/Pure/term_xml.scala

clarified signature, following zterm.ML;

/*  Title:      Pure/term_xml.scala
    Author:     Makarius

XML data representation of lambda terms.
*/

package isabelle


object Term_XML {
  import Term._

  object Encode {
    import XML.Encode._

    val indexname: P[Indexname] =
      { case Indexname(a, 0) => List(a)
        case Indexname(a, b) => List(a, int_atom(b)) }

    val sort: T[Sort] = list(string)

    def typ: T[Typ] =
      variant[Typ](List(
        { case Type(a, b) => (List(a), list(typ)(b)) },
        { case TFree(a, b) => (List(a), sort(b)) },
        { case TVar(a, b) => (indexname(a), sort(b)) }))

    private val var_type: T[Typ] = (t: Typ) => if (t == dummyT) Nil else typ(t)

    def term: T[Term] =
      variant[Term](List(
        { case Const(a, b) => (List(a), list(typ)(b)) },
        { case Free(a, b) => (List(a), var_type(b)) },
        { case Var(a, b) => (indexname(a), var_type(b)) },
        { case Bound(a) => (Nil, int(a)) },
        { case Abs(a, b, c) => (List(a), pair(typ, term)(b, c)) },
        { case App(a, b) => (Nil, pair(term, term)(a, b)) },
        { case OFCLASS(a, b) => (List(b), typ(a)) }))
  }

  object Decode {
    import XML.Decode._

    val indexname: P[Indexname] =
      { case List(a) => Indexname(a, 0)
        case List(a, b) => Indexname(a, int_atom(b)) }

    val sort: T[Sort] = list(string)

    def typ: T[Typ] =
      variant[Typ](List(
        { case (List(a), b) => Type(a, list(typ)(b)) },
        { case (List(a), b) => TFree(a, sort(b)) },
        { case (a, b) => TVar(indexname(a), sort(b)) }))

    private val var_type: T[Typ] = { case Nil => dummyT case body => typ(body) }

    def term: T[Term] =
      variant[Term](List(
        { case (List(a), b) => Const(a, list(typ)(b)) },
        { case (List(a), b) => Free(a, var_type(b)) },
        { case (a, b) => Var(indexname(a), var_type(b)) },
        { case (Nil, a) => Bound(int(a)) },
        { case (List(a), b) => val (c, d) = pair(typ, term)(b); Abs(a, c, d) },
        { case (Nil, a) => val (b, c) = pair(term, term)(a); App(b, c) },
        { case (List(a), b) => OFCLASS(typ(b), a) }))

    def term_env(env: Map[String, Typ]): T[Term] = {
      def env_type(x: String, t: Typ): Typ =
        if (t == dummyT && env.isDefinedAt(x)) env(x) else t

      def term: T[Term] =
        variant[Term](List(
          { case (List(a), b) => Const(a, list(typ)(b)) },
          { case (List(a), b) => Free(a, env_type(a, var_type(b))) },
          { case (a, b) => Var(indexname(a), var_type(b)) },
          { case (Nil, a) => Bound(int(a)) },
          { case (List(a), b) => val (c, d) = pair(typ, term)(b); Abs(a, c, d) },
          { case (Nil, a) => val (b, c) = pair(term, term)(a); App(b, c) },
          { case (List(a), b) => OFCLASS(typ(b), a) }))
      term
    }

    def proof_env(env: Map[String, Typ]): T[Proof] = {
      val term = term_env(env)
      def proof: T[Proof] =
        variant[Proof](List(
          { case (Nil, Nil) => MinProof },
          { case (Nil, a) => PBound(int(a)) },
          { case (List(a), b) => val (c, d) = pair(typ, proof)(b); Abst(a, c, d) },
          { case (List(a), b) => val (c, d) = pair(term, proof)(b); AbsP(a, c, d) },
          { case (Nil, a) => val (b, c) = pair(proof, term)(a); Appt(b, c) },
          { case (Nil, a) => val (b, c) = pair(proof, proof)(a); AppP(b, c) },
          { case (Nil, a) => Hyp(term(a)) },
          { case (List(a), b) => PAxm(a, list(typ)(b)) },
          { case (List(a), b) => PClass(typ(b), a) },
          { case (List(a), b) => val (c, d) = pair(term, list(typ))(b); Oracle(a, c, d) },
          { case (List(a, b, c, d), e) =>
            PThm(long_atom(a), b, Thm_Name(c, int_atom(d)), list(typ)(e))
          }))
      proof
    }

    val proof: T[Proof] = proof_env(Map.empty)
  }
}