(* Title: Provers/induct_method.ML
ID: $Id$
Author: Markus Wenzel, TU Muenchen
Proof by cases and induction on sets and types.
*)
signature INDUCT_METHOD_DATA =
sig
val dest_concls: term -> term list
val cases_default: thm
val local_impI: thm
val conjI: thm
val atomize: thm list
val rulify1: thm list
val rulify2: thm list
val localize: thm list
end;
signature INDUCT_METHOD =
sig
val cases_tac: Proof.context -> bool -> term option list list -> thm option ->
thm list -> int -> RuleCases.tactic
val induct_tac: Proof.context -> bool -> term option list list ->
thm option -> (string * typ) list -> thm list -> int -> RuleCases.tactic
val setup: (theory -> theory) list
end;
functor InductMethodFun(Data: INDUCT_METHOD_DATA): INDUCT_METHOD =
struct
(** misc utils **)
(* align lists *)
fun align_left msg xs ys =
let val m = length xs and n = length ys
in if m < n then raise ERROR_MESSAGE msg else (Library.take (n, xs) ~~ ys) end;
fun align_right msg xs ys =
let val m = length xs and n = length ys
in if m < n then raise ERROR_MESSAGE msg else (Library.drop (m - n, xs) ~~ ys) end;
(* prep_inst *)
fun prep_inst align cert tune (tm, ts) =
let
fun prep_var (x, SOME t) =
let
val cx = cert x;
val {T = xT, thy, ...} = Thm.rep_cterm cx;
val ct = cert (tune t);
in
if Sign.typ_instance thy (#T (Thm.rep_cterm ct), xT) then SOME (cx, ct)
else raise ERROR_MESSAGE (Pretty.string_of (Pretty.block
[Pretty.str "Ill-typed instantiation:", Pretty.fbrk,
Display.pretty_cterm ct, Pretty.str " ::", Pretty.brk 1,
Display.pretty_ctyp (#T (Thm.crep_cterm ct))]))
end
| prep_var (_, NONE) = NONE;
val xs = InductAttrib.vars_of tm;
in
align "Rule has fewer variables than instantiations given" xs ts
|> List.mapPartial prep_var
end;
(** cases method **)
(*
rule selection scheme:
cases - classical case split
<x:A> cases ... - set cases
cases t - type cases
... cases ... R - explicit rule
*)
local
fun resolveq_cases_tac make ruleq i st =
ruleq |> Seq.maps (fn (rule, (cases, facts)) =>
(Method.insert_tac facts THEN' Tactic.rtac rule) i st
|> Seq.map (rpair (make (Thm.theory_of_thm rule, Thm.prop_of rule) cases)));
fun find_casesT ctxt ((SOME t :: _) :: _) = InductAttrib.find_casesT ctxt (fastype_of t)
| find_casesT _ _ = [];
fun find_casesS ctxt (fact :: _) = InductAttrib.find_casesS ctxt fact
| find_casesS _ _ = [];
in
fun cases_tac ctxt is_open insts opt_rule facts =
let
val thy = ProofContext.theory_of ctxt;
val cert = Thm.cterm_of thy;
fun inst_rule r =
if null insts then RuleCases.add r
else (align_left "Rule has fewer premises than arguments given" (Thm.prems_of r) insts
|> (List.concat o map (prep_inst align_left cert I))
|> Drule.cterm_instantiate) r |> rpair (RuleCases.get r);
val ruleq =
(case opt_rule of
NONE =>
let val rules = find_casesS ctxt facts @ find_casesT ctxt insts @ [Data.cases_default] in
Method.trace ctxt rules;
Seq.maps (Seq.try inst_rule) (Seq.of_list rules)
end
| SOME r => Seq.single (inst_rule r));
fun prep_rule (th, (cases, n)) = Seq.map (apsnd (rpair (Library.drop (n, facts))) o rpair cases)
(Method.multi_resolves (Library.take (n, facts)) [th]);
in resolveq_cases_tac (RuleCases.make is_open NONE) (Seq.maps prep_rule ruleq) end;
val cases_meth = Method.METHOD_CASES o ((Seq.DETERM o HEADGOAL) oo
(fn (ctxt, (is_open, (insts, opt_rule))) => cases_tac ctxt is_open insts opt_rule));
end;
(** induct method **)
(*
rule selection scheme:
<x:A> induct ... - set induction
induct x - type induction
... induct ... R - explicit rule
*)
local
(* atomize and rulify *)
fun atomize_term thy =
ObjectLogic.drop_judgment thy o MetaSimplifier.rewrite_term thy Data.atomize [];
fun rulified_term thm =
let val thy = Thm.theory_of_thm thm in
Thm.prop_of thm
|> MetaSimplifier.rewrite_term thy Data.rulify1 []
|> MetaSimplifier.rewrite_term thy Data.rulify2 []
|> pair thy
end;
val atomize_tac = Tactic.rewrite_goal_tac Data.atomize;
val rulify_tac =
Tactic.rewrite_goal_tac Data.rulify1 THEN'
Tactic.rewrite_goal_tac Data.rulify2 THEN'
Tactic.norm_hhf_tac;
val localize = Goal.norm_hhf o Tactic.simplify false Data.localize;
(* fix_tac *)
local
val meta_spec = PureThy.get_thm Pure.thy (Name "meta_spec");
fun meta_spec_tac ctxt (x, T) i st = SUBGOAL (fn (goal, _) =>
let
val thy = Thm.theory_of_thm st;
val cert = Thm.cterm_of thy;
val certT = Thm.ctyp_of thy;
val v = Free (x, T);
val _ = Term.exists_subterm (fn t => t aconv v) goal orelse
error ("No occurrence of " ^ ProofContext.string_of_term ctxt v ^ " in subgoal");
val P = Term.absfree (x, T, goal);
val rule = meta_spec
|> Drule.instantiate' [SOME (certT T)] [SOME (cert P), SOME (cert v)]
|> Thm.rename_params_rule ([x], 1);
in compose_tac (false, rule, 1) end i) i st;
in
fun fix_tac ctxt fixes = EVERY' (map (meta_spec_tac ctxt) (rev fixes));
end;
(* internalize implications -- limited to atomic prems *)
local
fun imp_intr i raw_th =
let
val th = Thm.permute_prems (i - 1) 1 raw_th;
val {thy, maxidx, ...} = Thm.rep_thm th;
val cprems = Drule.cprems_of th;
val As = Library.take (length cprems - 1, cprems);
val C = Thm.cterm_of thy (Var (("C", maxidx + 1), propT));
in th COMP Thm.lift_rule (Drule.list_implies (As, C)) Data.local_impI end;
in
fun internalize k th = if k > 0 then internalize (k - 1) (imp_intr k th) else th;
end;
(* join multi-rules *)
val eq_prems = curry (Term.aconvs o pairself Thm.prems_of);
fun join_rules [] = []
| join_rules [th] = [th]
| join_rules (rules as r :: rs) =
if not (forall (eq_prems r) rs) then []
else
let
val th :: ths = map Drule.freeze_all rules;
val cprems = Drule.cprems_of th;
val asms = map Thm.assume cprems;
in
[foldr1 (fn (x, x') => [x, x'] MRS Data.conjI)
(map (fn x => Drule.implies_elim_list x asms) (th :: ths))
|> Drule.implies_intr_list cprems
|> Drule.standard'
|> RuleCases.save r]
end;
(* divinate rule instantiation (cannot handle pending goal parameters) *)
fun dest_env thy (env as Envir.Envir {iTs, ...}) =
let
val cert = Thm.cterm_of thy;
val certT = Thm.ctyp_of thy;
val pairs = Envir.alist_of env;
val ts = map (cert o Envir.norm_term env o #2 o #2) pairs;
val xs = map2 (cert o Var) (map #1 pairs, map (#T o Thm.rep_cterm) ts);
in (map (fn (xi, (S, T)) => (certT (TVar (xi, S)), certT T)) (Vartab.dest iTs), xs ~~ ts) end;
fun divinate_inst rule i st =
let
val {thy, maxidx, ...} = Thm.rep_thm st;
val goal = Thm.term_of (Thm.cprem_of st i); (*exception Subscript*)
val params = rev (rename_wrt_term goal (Logic.strip_params goal)); (*as they are printed :-*)
in
if not (null params) then
(warning ("Cannot determine rule instantiation due to pending parameter(s): " ^
commas (map (Sign.string_of_term thy o Syntax.mark_boundT) params));
Seq.single rule)
else
let
val rule' = Thm.incr_indexes (maxidx + 1) rule;
val concl = Logic.strip_assums_concl goal;
in
Unify.smash_unifiers (thy, Envir.empty (#maxidx (Thm.rep_thm rule')),
[(Thm.concl_of rule', concl)])
|> Seq.map (fn env => Drule.instantiate (dest_env thy env) rule')
end
end handle Subscript => Seq.empty;
(* compose tactics with cases *)
fun resolveq_cases_tac' ctxt make is_open ruleq fixes i st =
ruleq |> Seq.maps (fn (rule, (cases, k, more_facts)) =>
(Method.insert_tac more_facts THEN' fix_tac ctxt fixes THEN' atomize_tac) i st
|> Seq.maps (fn st' =>
divinate_inst (internalize k rule) i st'
|> Seq.maps (fn rule' =>
Tactic.rtac rule' i st'
|> Seq.map (rpair (make is_open (SOME (Thm.prop_of rule')) (rulified_term rule') cases)))));
infix 1 THEN_ALL_NEW_CASES;
fun (tac1 THEN_ALL_NEW_CASES tac2) i st =
st |> tac1 i |> Seq.maps (fn (st', cases) =>
Seq.map (rpair cases) (Seq.INTERVAL tac2 i (i + nprems_of st' - nprems_of st) st'));
(* find rules *)
(*rename all outermost !!-bound vars of type T in all premises of thm to x,
possibly indexed to avoid clashes*)
fun rename [[SOME (Free (x, Type (T, _)))]] thm =
let
fun index i [] = []
| index i (y :: ys) =
if x = y then x ^ string_of_int i :: index (i + 1) ys
else y :: index i ys;
fun rename_params [] = []
| rename_params ((y, Type (U, _)) :: ys) =
(if U = T then x else y) :: rename_params ys
| rename_params ((y, _) :: ys) = y :: rename_params ys;
fun rename_asm A =
let
val xs = rename_params (Logic.strip_params A);
val xs' =
(case List.filter (equal x) xs of
[] => xs | [_] => xs | _ => index 1 xs);
in Logic.list_rename_params (xs', A) end;
fun rename_prop p =
let val (As, C) = Logic.strip_horn p
in Logic.list_implies (map rename_asm As, C) end;
val cp' = cterm_fun rename_prop (Thm.cprop_of thm);
val thm' = Thm.equal_elim (Thm.reflexive cp') thm;
in Thm.put_name_tags (Thm.get_name_tags thm) thm' end
| rename _ thm = thm;
fun find_inductT ctxt insts =
fold_rev multiply (insts |> List.mapPartial (fn [] => NONE | ts => List.last ts)
|> map (InductAttrib.find_inductT ctxt o fastype_of)) [[]]
|> map join_rules |> List.concat |> map (rename insts);
fun find_inductS ctxt (fact :: _) = InductAttrib.find_inductS ctxt fact
| find_inductS _ _ = [];
in
(* main tactic *)
fun induct_tac ctxt is_open insts opt_rule fixes facts =
let
val thy = ProofContext.theory_of ctxt;
val cert = Thm.cterm_of thy;
fun rule_versions r = Seq.cons (r, Seq.filter (not o curry Thm.eq_thm r)
(Seq.make (fn () => SOME (localize r, Seq.empty))))
|> Seq.map (rpair (RuleCases.get r));
val inst_rule = apfst (fn r =>
if null insts then r
else (align_right "Rule has fewer conclusions than arguments given"
(Data.dest_concls (Thm.concl_of r)) insts
|> (List.concat o map (prep_inst align_right cert (atomize_term thy)))
|> Drule.cterm_instantiate) r);
val ruleq =
(case opt_rule of
NONE =>
let val rules = find_inductS ctxt facts @ find_inductT ctxt insts in
conditional (null rules) (fn () => error "Unable to figure out induct rule");
Method.trace ctxt rules;
rules |> Seq.of_list |> Seq.maps rule_versions |> Seq.maps (Seq.try inst_rule)
end
| SOME r => r |> rule_versions |> Seq.map inst_rule);
fun prep_rule (th, (cases, n)) =
Seq.map (rpair (cases, n - length facts, Library.drop (n, facts)))
(Method.multi_resolves (Library.take (n, facts)) [th]);
val tac = resolveq_cases_tac' ctxt RuleCases.make is_open (Seq.maps prep_rule ruleq) fixes;
in tac THEN_ALL_NEW_CASES rulify_tac end;
val induct_meth = Method.RAW_METHOD_CASES o ((Seq.DETERM o HEADGOAL) oo
(fn (ctxt, (is_open, (insts, (opt_rule, fixes)))) =>
induct_tac ctxt is_open insts opt_rule fixes));
end;
(** concrete syntax **)
val openN = "open";
val ruleN = "rule";
val ofN = "of";
val fixingN = "fixing";
local
fun named_rule k arg get =
Scan.lift (Args.$$$ k -- Args.colon) |-- arg :-- (fn name => Scan.peek (fn ctxt =>
(case get ctxt name of SOME x => Scan.succeed x
| NONE => error ("No rule for " ^ k ^ " " ^ quote name)))) >> #2;
fun rule get_type get_set =
named_rule InductAttrib.typeN Args.local_tyname get_type ||
named_rule InductAttrib.setN Args.local_const get_set ||
Scan.lift (Args.$$$ ruleN -- Args.colon) |-- Attrib.local_thm;
val cases_rule = rule InductAttrib.lookup_casesT InductAttrib.lookup_casesS;
val induct_rule = rule InductAttrib.lookup_inductT InductAttrib.lookup_inductS;
val more_args =
(Args.$$$ InductAttrib.typeN || Args.$$$ InductAttrib.setN || Args.$$$ ruleN ||
Args.$$$ ofN || Args.$$$ fixingN) -- Args.colon;
val term = Scan.unless (Scan.lift more_args) Args.local_term;
val term_dummy = Scan.unless (Scan.lift more_args)
(Scan.lift (Args.$$$ "_") >> K NONE || Args.local_term >> SOME);
val instss = Args.and_list (Scan.repeat term_dummy);
val free = Scan.state -- Args.local_term >> (fn (_, Free v) => v | (ctxt, t) =>
error ("Bad free variable: " ^ ProofContext.string_of_term ctxt t));
val fixing = Scan.optional (Scan.lift (Args.$$$ fixingN -- Args.colon) |-- Scan.repeat1 free) [];
in
val cases_args =
Method.syntax (Args.mode openN -- (instss -- Scan.option cases_rule));
val induct_args =
Method.syntax (Args.mode openN -- (instss -- (Scan.option induct_rule -- fixing)));
end;
(** theory setup **)
val setup =
[Method.add_methods
[(InductAttrib.casesN, cases_meth oo cases_args, "case analysis on types or sets"),
(InductAttrib.inductN, induct_meth oo induct_args, "induction on types or sets")]];
end;