(** * Deterministic worlds *)

(** One source of possible nondeterminism is that our semantics leave
  unspecified the results of system calls.
  Different results to e.g. a "read" operation can of
  course lead to different behaviors for the program.
  We address this issue by modeling a notion of deterministic
  external world that uniquely determines the results of external calls. *)

(** An external world is a function that, given the name of an
  external call and its arguments, returns either [None], meaning
  that this external call gets stuck, or [Some(r,w)], meaning
  that this external call succeeds, has result [r], and changes
  the world to [w]. *)

CoInductive world: Type :=
  World (io: string -> list eventval -> option (eventval * world))
        (vload: memory_chunk -> ident -> ptrofs -> option (eventval * world))
        (vstore: memory_chunk -> ident -> ptrofs -> eventval -> option world).(** * Deterministic worlds *)

(** One source of possible nondeterminism is that our semantics leave
  unspecified the results of system calls.
  Different results to e.g. a "read" operation can of
  course lead to different behaviors for the program.
  We address this issue by modeling a notion of deterministic
  external world that uniquely determines the results of external calls. *)

(** An external world is a function that, given the name of an
  external call and its arguments, returns either [None], meaning
  that this external call gets stuck, or [Some(r,w)], meaning
  that this external call succeeds, has result [r], and changes
  the world to [w]. *)

CoInductive world: Type :=
  World (io: string -> list eventval -> option (eventval * world))
        (vload: memory_chunk -> ident -> ptrofs -> option (eventval * world))
        (vstore: memory_chunk -> ident -> ptrofs -> eventval -> option world).Definition nextworld_io (w: world) (evname: string) (evargs: list eventval) :
                     option (eventval * world) :=
  match w with World io vl vs => io evname evargs end.Definition nextworld_vload (w: world) (chunk: memory_chunk) (id: ident) (ofs: ptrofs) :
                     option (eventval * world) :=
  match w with World io vl vs => vl chunk id ofs end.Definition nextworld_vstore (w: world) (chunk: memory_chunk) (id: ident) (ofs: ptrofs) (v: eventval):
                     option world :=
  match w with World io vl vs => vs chunk id ofs v end.(** A trace is possible in a given world if all events correspond
  to non-stuck external calls according to the given world.
  Two predicates are defined, for finite and infinite traces respectively:
- [possible_trace w t w'], where [w] is the initial state of the
  world, [t] the finite trace of interest, and [w'] the state of the
  world after performing trace [t].
- [possible_traceinf w T], where [w] is the initial state of the
  world and [T] the infinite trace of interest.
*)

Inductive possible_event: world -> event -> world -> Prop :=
  | possible_event_syscall: forall w1 evname evargs evres w2,
      nextworld_io w1 evname evargs = Some (evres, w2) ->
      possible_event w1 (Event_syscall evname evargs evres) w2
  | possible_event_vload: forall w1 chunk id ofs evres w2,
      nextworld_vload w1 chunk id ofs = Some (evres, w2) ->
      possible_event w1 (Event_vload chunk id ofs evres) w2
  | possible_event_vstore: forall w1 chunk id ofs evarg w2,
      nextworld_vstore w1 chunk id ofs evarg = Some w2 ->
      possible_event w1 (Event_vstore chunk id ofs evarg) w2
  | possible_event_annot: forall w1 id args,
      possible_event w1 (Event_annot id args) w1.(** A trace is possible in a given world if all events correspond
  to non-stuck external calls according to the given world.
  Two predicates are defined, for finite and infinite traces respectively:
- [possible_trace w t w'], where [w] is the initial state of the
  world, [t] the finite trace of interest, and [w'] the state of the
  world after performing trace [t].
- [possible_traceinf w T], where [w] is the initial state of the
  world and [T] the infinite trace of interest.
*)

Inductive possible_event: world -> event -> world -> Prop :=
  | possible_event_syscall: forall w1 evname evargs evres w2,
      nextworld_io w1 evname evargs = Some (evres, w2) ->
      possible_event w1 (Event_syscall evname evargs evres) w2
  | possible_event_vload: forall w1 chunk id ofs evres w2,
      nextworld_vload w1 chunk id ofs = Some (evres, w2) ->
      possible_event w1 (Event_vload chunk id ofs evres) w2
  | possible_event_vstore: forall w1 chunk id ofs evarg w2,
      nextworld_vstore w1 chunk id ofs evarg = Some w2 ->
      possible_event w1 (Event_vstore chunk id ofs evarg) w2
  | possible_event_annot: forall w1 id args,
      possible_event w1 (Event_annot id args) w1.(** A trace is possible in a given world if all events correspond
  to non-stuck external calls according to the given world.
  Two predicates are defined, for finite and infinite traces respectively:
- [possible_trace w t w'], where [w] is the initial state of the
  world, [t] the finite trace of interest, and [w'] the state of the
  world after performing trace [t].
- [possible_traceinf w T], where [w] is the initial state of the
  world and [T] the infinite trace of interest.
*)

Inductive possible_event: world -> event -> world -> Prop :=
  | possible_event_syscall: forall w1 evname evargs evres w2,
      nextworld_io w1 evname evargs = Some (evres, w2) ->
      possible_event w1 (Event_syscall evname evargs evres) w2
  | possible_event_vload: forall w1 chunk id ofs evres w2,
      nextworld_vload w1 chunk id ofs = Some (evres, w2) ->
      possible_event w1 (Event_vload chunk id ofs evres) w2
  | possible_event_vstore: forall w1 chunk id ofs evarg w2,
      nextworld_vstore w1 chunk id ofs evarg = Some w2 ->
      possible_event w1 (Event_vstore chunk id ofs evarg) w2
  | possible_event_annot: forall w1 id args,
      possible_event w1 (Event_annot id args) w1.(** A trace is possible in a given world if all events correspond
  to non-stuck external calls according to the given world.
  Two predicates are defined, for finite and infinite traces respectively:
- [possible_trace w t w'], where [w] is the initial state of the
  world, [t] the finite trace of interest, and [w'] the state of the
  world after performing trace [t].
- [possible_traceinf w T], where [w] is the initial state of the
  world and [T] the infinite trace of interest.
*)

Inductive possible_event: world -> event -> world -> Prop :=
  | possible_event_syscall: forall w1 evname evargs evres w2,
      nextworld_io w1 evname evargs = Some (evres, w2) ->
      possible_event w1 (Event_syscall evname evargs evres) w2
  | possible_event_vload: forall w1 chunk id ofs evres w2,
      nextworld_vload w1 chunk id ofs = Some (evres, w2) ->
      possible_event w1 (Event_vload chunk id ofs evres) w2
  | possible_event_vstore: forall w1 chunk id ofs evarg w2,
      nextworld_vstore w1 chunk id ofs evarg = Some w2 ->
      possible_event w1 (Event_vstore chunk id ofs evarg) w2
  | possible_event_annot: forall w1 id args,
      possible_event w1 (Event_annot id args) w1.(** A trace is possible in a given world if all events correspond
  to non-stuck external calls according to the given world.
  Two predicates are defined, for finite and infinite traces respectively:
- [possible_trace w t w'], where [w] is the initial state of the
  world, [t] the finite trace of interest, and [w'] the state of the
  world after performing trace [t].
- [possible_traceinf w T], where [w] is the initial state of the
  world and [T] the infinite trace of interest.
*)

Inductive possible_event: world -> event -> world -> Prop :=
  | possible_event_syscall: forall w1 evname evargs evres w2,
      nextworld_io w1 evname evargs = Some (evres, w2) ->
      possible_event w1 (Event_syscall evname evargs evres) w2
  | possible_event_vload: forall w1 chunk id ofs evres w2,
      nextworld_vload w1 chunk id ofs = Some (evres, w2) ->
      possible_event w1 (Event_vload chunk id ofs evres) w2
  | possible_event_vstore: forall w1 chunk id ofs evarg w2,
      nextworld_vstore w1 chunk id ofs evarg = Some w2 ->
      possible_event w1 (Event_vstore chunk id ofs evarg) w2
  | possible_event_annot: forall w1 id args,
      possible_event w1 (Event_annot id args) w1.Inductive possible_trace: world -> trace -> world -> Prop :=
  | possible_trace_nil: forall w,
      possible_trace w E0 w
  | possible_trace_cons: forall w1 ev w2 t w3,
      possible_event w1 ev w2 -> possible_trace w2 t w3 ->
      possible_trace w1 (ev :: t) w3.Inductive possible_trace: world -> trace -> world -> Prop :=
  | possible_trace_nil: forall w,
      possible_trace w E0 w
  | possible_trace_cons: forall w1 ev w2 t w3,
      possible_event w1 ev w2 -> possible_trace w2 t w3 ->
      possible_trace w1 (ev :: t) w3.Inductive possible_trace: world -> trace -> world -> Prop :=
  | possible_trace_nil: forall w,
      possible_trace w E0 w
  | possible_trace_cons: forall w1 ev w2 t w3,
      possible_event w1 ev w2 -> possible_trace w2 t w3 ->
      possible_trace w1 (ev :: t) w3.

Lemma match_possible_traces: forall ge t1 t2 w0 w1 w2, match_traces ge t1 t2 -> possible_trace w0 t1 w1 -> possible_trace w0 t2 w2 -> t1 = t2 /\ w1 = w2.