(*  Title:      Pure/subgoal.ML

    ID:         $Id$

    Author:     Makarius

Tactical operations depending on local subgoal structure.

*)

signature BASIC_SUBGOAL =

sig

  val SUBPROOF:

    ({context: Proof.context, schematics: ctyp list * cterm list,

      params: cterm list, asms: cterm list, concl: cterm,

      prems: thm list} -> tactic) -> Proof.context -> int -> tactic

end

signature SUBGOAL =

sig

  include BASIC_SUBGOAL

  val focus: Proof.context -> int -> thm ->

   {context: Proof.context, schematics: ctyp list * cterm list,

    params: cterm list, asms: cterm list, concl: cterm, prems: thm list} * thm

end;

structure Subgoal: SUBGOAL =

struct

(* canonical proof decomposition -- similar to fix/assume/show *)

fun focus ctxt i st =

  let

    val ((schematics, [st']), ctxt') = Variable.import true [norm_hhf st] ctxt;

    val ((params, goal), ctxt'') = Variable.focus_subgoal i st' ctxt';

    val asms = Drule.strip_imp_prems goal;

    val concl = Drule.strip_imp_concl goal;

    val (prems, context) = Assumption.add_assumes asms ctxt'';

  in

    ({context = context, schematics = schematics, params = params,

      asms = asms, concl = concl, prems = prems}, Goal.init concl)

  end;

fun SUBPROOF tac ctxt i st =

  if Thm.nprems_of st < i then Seq.empty

  else

    let

      val (args as {context, params, ...}, st') = focus ctxt i st;

      fun export_closed th =

        let

          val (th' :: params') = ProofContext.export context ctxt (th :: map Drule.mk_term params);

          val vs = map (#2 o Thm.dest_comb o Drule.strip_imp_concl o Thm.cprop_of) params';

        in Drule.forall_intr_list vs th' end;

      fun retrofit th = Thm.compose_no_flatten false (th, 0) i;

    in Seq.lifts retrofit (Seq.map (Goal.finish #> export_closed) (tac args st')) st end

end;

structure BasicSubgoal: BASIC_SUBGOAL = Subgoal;

open BasicSubgoal;