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(* Title: FOLP/hypsubst.ML
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Author: Martin D Coen, Cambridge University Computer Laboratory
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Copyright 1995 University of Cambridge
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Original version of Provers/hypsubst. Cannot use new version because it
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relies on the new simplifier!
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Martin Coen's tactic for substitution in the hypotheses
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*)
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signature HYPSUBST_DATA =
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sig
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val dest_eq : term -> term*term
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val imp_intr : thm (* (P ==> Q) ==> P-->Q *)
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val rev_mp : thm (* [| P; P-->Q |] ==> Q *)
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val subst : thm (* [| a=b; P(a) |] ==> P(b) *)
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val sym : thm (* a=b ==> b=a *)
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end;
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signature HYPSUBST =
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sig
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val bound_hyp_subst_tac : int -> tactic
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val hyp_subst_tac : int -> tactic
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(*exported purely for debugging purposes*)
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val eq_var : bool -> term -> int * thm
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val inspect_pair : bool -> term * term -> thm
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end;
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functor Hypsubst(Data: HYPSUBST_DATA): HYPSUBST =
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struct
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local open Data in
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exception EQ_VAR;
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(*It's not safe to substitute for a constant; consider 0=1.
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It's not safe to substitute for x=t[x] since x is not eliminated.
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It's not safe to substitute for a Var; what if it appears in other goals?
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It's not safe to substitute for a variable free in the premises,
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but how could we check for this?*)
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fun inspect_pair bnd (t, u) =
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(case (Envir.eta_contract t, Envir.eta_contract u) of
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(Bound i, _) =>
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if loose_bvar1 (u, i) then raise Match
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else sym (*eliminates t*)
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| (_, Bound i) =>
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if loose_bvar (t, i) then raise Match
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else asm_rl (*eliminates u*)
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| (Free _, _) =>
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if bnd orelse Logic.occs (t, u) then raise Match
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else sym (*eliminates t*)
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| (_, Free _) =>
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if bnd orelse Logic.occs(u,t) then raise Match
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else asm_rl (*eliminates u*)
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| _ => raise Match);
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(*Locates a substitutable variable on the left (resp. right) of an equality
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assumption. Returns the number of intervening assumptions, paried with
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the rule asm_rl (resp. sym). *)
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fun eq_var bnd =
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let fun eq_var_aux k (Const("all",_) $ Abs(_,_,t)) = eq_var_aux k t
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| eq_var_aux k (Const("==>",_) $ A $ B) =
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((k, inspect_pair bnd (dest_eq A))
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(*Exception Match comes from inspect_pair or dest_eq*)
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handle Match => eq_var_aux (k+1) B)
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| eq_var_aux k _ = raise EQ_VAR
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in eq_var_aux 0 end;
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(*Select a suitable equality assumption and substitute throughout the subgoal
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Replaces only Bound variables if bnd is true*)
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fun gen_hyp_subst_tac bnd = SUBGOAL(fn (Bi,i) =>
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let val n = length(Logic.strip_assums_hyp Bi) - 1
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val (k,symopt) = eq_var bnd Bi
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in
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DETERM
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(EVERY [REPEAT_DETERM_N k (etac rev_mp i),
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etac revcut_rl i,
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REPEAT_DETERM_N (n-k) (etac rev_mp i),
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etac (symopt RS subst) i,
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REPEAT_DETERM_N n (rtac imp_intr i)])
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end
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handle THM _ => no_tac | EQ_VAR => no_tac);
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(*Substitutes for Free or Bound variables*)
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val hyp_subst_tac = gen_hyp_subst_tac false;
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(*Substitutes for Bound variables only -- this is always safe*)
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val bound_hyp_subst_tac = gen_hyp_subst_tac true;
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end
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end;
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