(* Copyright 2010 IMDEA Software Institute Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. *)
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(* This file defines heaps as possibly undefined finite maps from pointer     *)
(* type to dynamic type.                                                      *)
(* Heaps are a special case of Partial Commutative Monoids (pcm)              *)
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Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.
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(* Locations *)
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Inductive ptr := ptr_nat of nat.
Definition null := ptr_nat 0.
Definition nat_ptr (x : ptr) := let: ptr_nat y := x in y.
Definition eq_ptr (x y : ptr) : bool :=
match x, y with ptr_nat m, ptr_nat n => m == n end.
Definition ltn_ptr (x y : ptr) :=
match x, y with ptr_nat m, ptr_nat n => m < n end.
End NullLemmas.
(* methods *)
Definition def h := if h is Def _ _ then true else false.
Definition empty := @Def (finmap.nil _ _) is_true_true.
Definition upd k v h :=
if h is Def hs ns then
if decP (@idP (k != null)) is left pf then
Def (@upd_nullP _ _ v pf ns)
else Undef
else Undef.
Definition dom h : seq ptr :=
if h is Def f _ then supp f else [::].
Definition dom_eq h1 h2 :=
match h1, h2 with
Def f1 _, Def f2 _ => supp f1 == supp f2
| Undef, Undef => true
| _, _ => false
end.
Definition free x h :=
if h is Def hs ns then Def (free_nullP x ns) else Undef.
Definition find (x : ptr) h :=
if h is Def hs _ then fnd x hs else None.
Definition union h1 h2 :=
if (h1, h2) is (Def hs1 ns1, Def hs2 ns2) then
if disj hs1 hs2 then
Def (@un_nullP _ _ ns1 ns2)
else Undef
else Undef.
Definition um_filter q f :=
if f is Def fs pf then Def (@filt_nullP fs q pf) else Undef.
Definition pts (x : ptr) v := upd x v empty.
Definition empb h := if h is Def hs _ then supp hs == [::] else false.
Definition undefb h := if h is Undef then true else false.
Definition keys_of h : seq ptr :=
if h is Def f _ then supp f else [::].
Local Notation base :=
(@UM.base ptr_ordType (dynamic id) (fun k => k != null)).
Definition from (f : heap) : base :=
if f is Def hs ns then UM.Def (heap_base ns) else UM.Undef _ _.
Definition to (b : base) : heap :=
if b is UM.Def hs ns then Def (base_heap ns) else Undef.

Lemma ftE b : from (to b) = b.