(* Title: HOL/Tools/Function/function_elims.ML
Author: Manuel Eberl, TU Muenchen
Generates the pelims rules for a function. These are of the shape
[|f x y z = w; !!…. [|x = …; y = …; z = …; w = …|] ==> P; …|] ==> P
and are derived from the cases rule. There is at least one pelim rule for
each function (cf. mutually recursive functions)
There may be more than one pelim rule for a function in case of functions
that return a boolean. For such a function, e.g. P x, not only the normal
elim rule with the premise P x = z is generated, but also two additional
elim rules with P x resp. ¬P x as premises.
*)
signature FUNCTION_ELIMS =
sig
val dest_funprop : term -> (term * term list) * term
val mk_partial_elim_rules :
local_theory -> Function_Common.function_result -> thm list list
end;
structure Function_Elims : FUNCTION_ELIMS =
struct
open Function_Lib
open Function_Common
(* Extracts a function and its arguments from a proposition that is
either of the form "f x y z = ..." or, in case of function that
returns a boolean, "f x y z" *)
fun dest_funprop (Const ("HOL.eq", _) $ lhs $ rhs) = (strip_comb lhs, rhs)
| dest_funprop (Const ("HOL.Not", _) $ trm) = (strip_comb trm, @{term "False"})
| dest_funprop trm = (strip_comb trm, @{term "True"});
local
fun propagate_tac i thm =
let fun inspect eq = case eq of
Const ("HOL.Trueprop",_) $ (Const ("HOL.eq",_) $ Free x $ t) =>
if Logic.occs (Free x, t) then raise Match else true
| Const ("HOL.Trueprop",_) $ (Const ("HOL.eq",_) $ t $ Free x) =>
if Logic.occs (Free x, t) then raise Match else false
| _ => raise Match;
fun mk_eq thm = (if inspect (prop_of thm) then
[thm RS eq_reflection]
else
[Thm.symmetric (thm RS eq_reflection)])
handle Match => [];
val ss = Simplifier.global_context (Thm.theory_of_thm thm) empty_ss
|> Simplifier.set_mksimps (K mk_eq)
in
asm_lr_simp_tac ss i thm
end;
val eqBoolI = @{lemma "!!P. P ==> P = True" "!!P. ~P ==> P = False" by iprover+}
val boolE = @{thms HOL.TrueE HOL.FalseE}
val boolD = @{lemma "!!P. True = P ==> P" "!!P. False = P ==> ~P" by iprover+}
val eqBool = @{thms HOL.eq_True HOL.eq_False HOL.not_False_eq_True HOL.not_True_eq_False}
fun bool_subst_tac ctxt i =
REPEAT (EqSubst.eqsubst_asm_tac ctxt [1] eqBool i)
THEN REPEAT (dresolve_tac boolD i)
THEN REPEAT (eresolve_tac boolE i)
fun mk_bool_elims ctxt elim =
let val tac = ALLGOALS (bool_subst_tac ctxt)
fun mk_bool_elim b =
elim
|> Thm.forall_elim b
|> Tactic.rule_by_tactic ctxt (TRY (resolve_tac eqBoolI 1))
|> Tactic.rule_by_tactic ctxt tac
in
map mk_bool_elim [@{cterm True}, @{cterm False}]
end;
in
fun mk_partial_elim_rules ctxt result=
let val FunctionResult {fs, G, R, dom, psimps, simple_pinducts, cases,
termination, domintros, ...} = result;
val n_fs = length fs;
fun mk_partial_elim_rule (idx,f) =
let fun mk_funeq 0 T (acc_vars, acc_lhs) =
let val y = Free("y",T) in
(y :: acc_vars, (HOLogic.mk_Trueprop (HOLogic.mk_eq (acc_lhs, y))), T)
end
| mk_funeq n (Type("fun",[S,T])) (acc_vars, acc_lhs) =
let val xn = Free ("x" ^ Int.toString n,S) in
mk_funeq (n - 1) T (xn :: acc_vars, acc_lhs $ xn)
end
| mk_funeq _ _ _ = raise (TERM ("Not a function.", [f]))
val f_simps = filter (fn r => (prop_of r |> Logic.strip_assums_concl
|> HOLogic.dest_Trueprop
|> dest_funprop |> fst |> fst) = f)
psimps
val arity = hd f_simps |> prop_of |> Logic.strip_assums_concl
|> HOLogic.dest_Trueprop
|> snd o fst o dest_funprop |> length;
val (free_vars,prop,ranT) = mk_funeq arity (fastype_of f) ([],f)
val (rhs_var, arg_vars) = case free_vars of x::xs => (x, rev xs)
val args = HOLogic.mk_tuple arg_vars;
val domT = R |> dest_Free |> snd |> hd o snd o dest_Type
val sumtree_inj = SumTree.mk_inj domT n_fs (idx+1) args;
val thy = Proof_Context.theory_of ctxt;
val cprop = cterm_of thy prop
val asms = [cprop, cterm_of thy (HOLogic.mk_Trueprop (dom $ sumtree_inj))];
val asms_thms = map Thm.assume asms;
fun prep_subgoal i =
REPEAT (eresolve_tac @{thms Pair_inject} i)
THEN Method.insert_tac (case asms_thms of
thm::thms => (thm RS sym) :: thms) i
THEN propagate_tac i
THEN TRY
((EqSubst.eqsubst_asm_tac ctxt [1] psimps i) THEN atac i)
THEN bool_subst_tac ctxt i;
val tac = ALLGOALS prep_subgoal;
val elim_stripped =
nth cases idx
|> Thm.forall_elim @{cterm "P::bool"}
|> Thm.forall_elim (cterm_of thy args)
|> Tactic.rule_by_tactic ctxt tac
|> fold_rev Thm.implies_intr asms
|> Thm.forall_intr (cterm_of thy rhs_var)
val bool_elims = (case ranT of
Type ("HOL.bool", []) => mk_bool_elims ctxt elim_stripped
| _ => []);
fun unstrip rl =
rl |> (fn thm => List.foldr (uncurry Thm.forall_intr) thm
(map (cterm_of thy) arg_vars))
|> Thm.forall_intr @{cterm "P::bool"}
in
map unstrip (elim_stripped :: bool_elims)
end;
in
map_index mk_partial_elim_rule fs
end;
end;
end;