wenzelm@59931: (*  Title:      Tools/induction.ML
wenzelm@59931:     Author:     Tobias Nipkow, TU Muenchen
wenzelm@59931: 
wenzelm@59931: Alternative proof method "induction" that gives induction hypotheses the
wenzelm@59931: name "IH".
wenzelm@59931: *)
wenzelm@59931: 
nipkow@45014: signature INDUCTION =
nipkow@45014: sig
wenzelm@59931:   val induction_tac: Proof.context -> bool ->
wenzelm@59931:     (binding option * (term * bool)) option list list ->
nipkow@45014:     (string * typ) list list -> term option list -> thm list option ->
nipkow@45014:     thm list -> int -> cases_tactic
nipkow@45014: end
nipkow@45014: 
nipkow@45014: structure Induction: INDUCTION =
nipkow@45014: struct
nipkow@45014: 
nipkow@45014: val ind_hypsN = "IH";
nipkow@45014: 
nipkow@45014: fun preds_of t =
wenzelm@59931:   (case strip_comb t of
nipkow@45014:     (p as Var _, _) => [p]
nipkow@45014:   | (p as Free _, _) => [p]
wenzelm@59931:   | (_, ts) => maps preds_of ts);
nipkow@45014: 
wenzelm@56506: fun name_hyps (arg as ((cases, consumes), th)) =
wenzelm@59931:   if not (forall (null o #2 o #1) cases) then arg
nipkow@45014:   else
nipkow@45014:     let
wenzelm@59582:       val (prems, concl) = Logic.strip_horn (Thm.prop_of th);
nipkow@45014:       val prems' = drop consumes prems;
nipkow@45014:       val ps = preds_of concl;
nipkow@45014: 
nipkow@45014:       fun hname_of t =
wenzelm@59931:         if exists_subterm (member (op aconv) ps) t
wenzelm@59931:         then ind_hypsN else Rule_Cases.case_hypsN;
nipkow@45014: 
wenzelm@59931:       val hnamess = map (map hname_of o Logic.strip_assums_hyp) prems';
wenzelm@59931:       val n = Int.min (length hnamess, length cases);
wenzelm@59931:       val cases' =
wenzelm@59931:         map (fn (((cn, _), concls), hns) => ((cn, hns), concls))
wenzelm@59931:           (take n cases ~~ take n hnamess);
wenzelm@59931:     in ((cases', consumes), th) end;
nipkow@45014: 
wenzelm@59931: val induction_tac = Induct.gen_induct_tac (K name_hyps);
nipkow@45014: 
wenzelm@59940: val _ = Theory.local_setup (Induct.gen_induct_setup @{binding induction} induction_tac);
nipkow@45014: 
nipkow@45014: end