(* Title: ZF/Tools/induct_tacs.ML
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1994 University of Cambridge
Induction and exhaustion tactics for Isabelle/ZF. The theory
information needed to support them (and to support primrec). Also a
function to install other sets as if they were datatypes.
*)
signature DATATYPE_TACTICS =
sig
val induct_tac: Proof.context -> string -> int -> tactic
val exhaust_tac: Proof.context -> string -> int -> tactic
val rep_datatype_i: thm -> thm -> thm list -> thm list -> theory -> theory
val rep_datatype: Facts.ref * Attrib.src list -> Facts.ref * Attrib.src list ->
(Facts.ref * Attrib.src list) list -> (Facts.ref * Attrib.src list) list -> theory -> theory
val setup: theory -> theory
end;
(** Datatype information, e.g. associated theorems **)
type datatype_info =
{inductive: bool, (*true if inductive, not coinductive*)
constructors : term list, (*the constructors, as Consts*)
rec_rewrites : thm list, (*recursor equations*)
case_rewrites : thm list, (*case equations*)
induct : thm,
mutual_induct : thm,
exhaustion : thm};
structure DatatypesData = Theory_Data
(
type T = datatype_info Symtab.table;
val empty = Symtab.empty;
val extend = I;
fun merge data : T = Symtab.merge (K true) data;
);
(** Constructor information: needed to map constructors to datatypes **)
type constructor_info =
{big_rec_name : string, (*name of the mutually recursive set*)
constructors : term list, (*the constructors, as Consts*)
free_iffs : thm list, (*freeness simprules*)
rec_rewrites : thm list}; (*recursor equations*)
structure ConstructorsData = Theory_Data
(
type T = constructor_info Symtab.table
val empty = Symtab.empty
val extend = I
fun merge data = Symtab.merge (K true) data;
);
structure DatatypeTactics : DATATYPE_TACTICS =
struct
fun datatype_info thy name =
(case Symtab.lookup (DatatypesData.get thy) name of
SOME info => info
| NONE => error ("Unknown datatype " ^ quote name));
(*Given a variable, find the inductive set associated it in the assumptions*)
exception Find_tname of string
fun find_tname ctxt var As =
let fun mk_pair (Const(@{const_name mem},_) $ Free (v,_) $ A) =
(v, #1 (dest_Const (head_of A)))
| mk_pair _ = raise Match
val pairs = map_filter (try (mk_pair o FOLogic.dest_Trueprop)) As
val x =
(case try (dest_Free o Syntax.read_term ctxt) var of
SOME (x, _) => x
| _ => raise Find_tname ("Bad variable " ^ quote var))
in case AList.lookup (op =) pairs x of
NONE => raise Find_tname ("Cannot determine datatype of " ^ quote var)
| SOME t => t
end;
(** generic exhaustion and induction tactic for datatypes
Differences from HOL:
(1) no checking if the induction var occurs in premises, since it always
appears in one of them, and it's hard to check for other occurrences
(2) exhaustion works for VARIABLES in the premises, not general terms
**)
fun exhaust_induct_tac exh ctxt var i state =
let
val thy = Proof_Context.theory_of ctxt
val ({context = ctxt', asms, ...}, _) = Subgoal.focus ctxt i state
val tn = find_tname ctxt' var (map term_of asms)
val rule =
if exh then #exhaustion (datatype_info thy tn)
else #induct (datatype_info thy tn)
val (Const(@{const_name mem},_) $ Var(ixn,_) $ _) =
(case prems_of rule of
[] => error "induction is not available for this datatype"
| major::_ => FOLogic.dest_Trueprop major)
in
eres_inst_tac ctxt [(ixn, var)] rule i state
end
handle Find_tname msg =>
if exh then (*try boolean case analysis instead*)
case_tac ctxt var i state
else error msg;
val exhaust_tac = exhaust_induct_tac true;
val induct_tac = exhaust_induct_tac false;
(**** declare non-datatype as datatype ****)
fun rep_datatype_i elim induct case_eqns recursor_eqns thy =
let
(*analyze the LHS of a case equation to get a constructor*)
fun const_of (Const(@{const_name IFOL.eq}, _) $ (_ $ c) $ _) = c
| const_of eqn = error ("Ill-formed case equation: " ^
Syntax.string_of_term_global thy eqn);
val constructors =
map (head_of o const_of o FOLogic.dest_Trueprop o Thm.prop_of) case_eqns;
val Const (@{const_name mem}, _) $ _ $ data =
FOLogic.dest_Trueprop (hd (prems_of elim));
val Const(big_rec_name, _) = head_of data;
val simps = case_eqns @ recursor_eqns;
val dt_info =
{inductive = true,
constructors = constructors,
rec_rewrites = recursor_eqns,
case_rewrites = case_eqns,
induct = induct,
mutual_induct = @{thm TrueI}, (*No need for mutual induction*)
exhaustion = elim};
val con_info =
{big_rec_name = big_rec_name,
constructors = constructors,
(*let primrec handle definition by cases*)
free_iffs = [], (*thus we expect the necessary freeness rewrites
to be in the simpset already, as is the case for
Nat and disjoint sum*)
rec_rewrites = (case recursor_eqns of
[] => case_eqns | _ => recursor_eqns)};
(*associate with each constructor the datatype name and rewrites*)
val con_pairs = map (fn c => (#1 (dest_Const c), con_info)) constructors
in
thy
|> Sign.add_path (Long_Name.base_name big_rec_name)
|> Global_Theory.add_thmss [((Binding.name "simps", simps), [Simplifier.simp_add])] |> snd
|> DatatypesData.put (Symtab.update (big_rec_name, dt_info) (DatatypesData.get thy))
|> ConstructorsData.put (fold_rev Symtab.update con_pairs (ConstructorsData.get thy))
|> Sign.parent_path
end;
fun rep_datatype raw_elim raw_induct raw_case_eqns raw_recursor_eqns thy =
let
val ctxt = Proof_Context.init_global thy;
val elim = Facts.the_single "elimination" (Attrib.eval_thms ctxt [raw_elim]);
val induct = Facts.the_single "induction" (Attrib.eval_thms ctxt [raw_induct]);
val case_eqns = Attrib.eval_thms ctxt raw_case_eqns;
val recursor_eqns = Attrib.eval_thms ctxt raw_recursor_eqns;
in rep_datatype_i elim induct case_eqns recursor_eqns thy end;
(* theory setup *)
val setup =
Method.setup @{binding induct_tac}
(Args.goal_spec -- Scan.lift Args.name >>
(fn (quant, s) => fn ctxt => SIMPLE_METHOD'' quant (induct_tac ctxt s)))
"induct_tac emulation (dynamic instantiation!)" #>
Method.setup @{binding case_tac}
(Args.goal_spec -- Scan.lift Args.name >>
(fn (quant, s) => fn ctxt => SIMPLE_METHOD'' quant (exhaust_tac ctxt s)))
"datatype case_tac emulation (dynamic instantiation!)";
(* outer syntax *)
val rep_datatype_decl =
(Parse.$$$ "elimination" |-- Parse.!!! Parse_Spec.xthm) --
(Parse.$$$ "induction" |-- Parse.!!! Parse_Spec.xthm) --
(Parse.$$$ "case_eqns" |-- Parse.!!! Parse_Spec.xthms1) --
Scan.optional (Parse.$$$ "recursor_eqns" |-- Parse.!!! Parse_Spec.xthms1) []
>> (fn (((x, y), z), w) => rep_datatype x y z w);
val _ =
Outer_Syntax.command "rep_datatype" "represent existing set inductively" Keyword.thy_decl
(rep_datatype_decl >> Toplevel.theory);
end;
val exhaust_tac = DatatypeTactics.exhaust_tac;
val induct_tac = DatatypeTactics.induct_tac;