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From stdpp Require Export binders strings.
From iris.prelude Require Import options.
From semantics.lib Require Export maps.
Declare Scope expr_scope.
Declare Scope val_scope.
Delimit Scope expr_scope with E.
Delimit Scope val_scope with V.
(** Expressions and vals. *)
Inductive base_lit : Set :=
| LitInt (n : Z) | LitBool (b : bool) | LitUnit.
Inductive un_op : Set :=
| NegOp | MinusUnOp.
Inductive bin_op : Set :=
| PlusOp | MinusOp | MultOp (* Arithmetic *)
| LtOp | LeOp | EqOp. (* Comparison *)
Inductive expr :=
| Lit (l : base_lit)
(* Base lambda calculus *)
| Var (x : string)
| Lam (x : binder) (e : expr)
| App (e1 e2 : expr)
(* Base types and their operations *)
| UnOp (op : un_op) (e : expr)
| BinOp (op : bin_op) (e1 e2 : expr)
| If (e0 e1 e2 : expr)
(* Polymorphism *)
| TApp (e : expr)
| TLam (e : expr)
| Pack (e : expr)
| Unpack (x : binder) (e1 e2 : expr)
(* Products *)
| Pair (e1 e2 : expr)
| Fst (e : expr)
| Snd (e : expr)
(* Sums *)
| InjL (e : expr)
| InjR (e : expr)
| Case (e0 : expr) (e1 : expr) (e2 : expr).
Bind Scope expr_scope with expr.
Inductive val :=
| LitV (l : base_lit)
| LamV (x : binder) (e : expr)
| TLamV (e : expr)
| PackV (v : val)
| PairV (v1 v2 : val)
| InjLV (v : val)
| InjRV (v : val)
.
Bind Scope val_scope with val.
Fixpoint of_val (v : val) : expr :=
match v with
| LitV l => Lit l
| LamV x e => Lam x e
| TLamV e => TLam e
| PackV v => Pack (of_val v)
| PairV v1 v2 => Pair (of_val v1) (of_val v2)
| InjLV v => InjL (of_val v)
| InjRV v => InjR (of_val v)
end.
Fixpoint to_val (e : expr) : option val :=
match e with
| Lit l => Some $ LitV l
| Lam x e => Some (LamV x e)
| TLam e => Some (TLamV e)
| Pack e =>
to_val e = (λ v, Some $ PackV v)
| Pair e1 e2 =>
to_val e1 = (λ v1, to_val e2 = (λ v2, Some $ PairV v1 v2))
| InjL e => to_val e = (λ v, Some $ InjLV v)
| InjR e => to_val e = (λ v, Some $ InjRV v)
| _ => None
end.
(** Equality and other typeclass stuff *)
Lemma to_of_val v : to_val (of_val v) = Some v.
Proof.
by induction v; simplify_option_eq; repeat f_equal; try apply (proof_irrel _).
Qed.
Lemma of_to_val e v : to_val e = Some v of_val v = e.
Proof.
revert v; induction e; intros v ?; simplify_option_eq; auto with f_equal.
Qed.
#[export] Instance of_val_inj : Inj (=) (=) of_val.
Proof. by intros ?? Hv; apply (inj Some); rewrite <-!to_of_val, Hv. Qed.
(** structural computational version *)
Fixpoint is_val (e : expr) : Prop :=
match e with
| Lit l => True
| Lam x e => True
| TLam e => True
| Pack e => is_val e
| Pair e1 e2 => is_val e1 is_val e2
| InjL e => is_val e
| InjR e => is_val e
| _ => False
end.
Lemma is_val_spec e : is_val e v, to_val e = Some v.
Proof.
induction e as [ | | ? e IH | e1 IH1 e2 IH2 | e IH | ? e1 IH1 e2 IH2 | e1 IH1 e2 IH2 e3 IH3 | e IH | e IH | e IH | ? e1 IH1 e2 IH2 | e1 IH1 e2 IH2 | e IH | e IH | e IH | e IH | e1 IH1 e2 IH2 e3 IH3 ];
simpl; (split; [ | intros (v & Heq)]); simplify_option_eq; try done; eauto.
- rewrite IH. intros (v & ->). eauto.
- apply IH. eauto.
- rewrite IH1, IH2. intros [(v1 & ->) (v2 & ->)]. eauto.
- rewrite IH1, IH2. eauto.
- rewrite IH. intros (v & ->). eauto.
- apply IH. eauto.
- rewrite IH. intros (v & ->); eauto.
- apply IH. eauto.
Qed.
Ltac simplify_val :=
repeat match goal with
| H: to_val (of_val ?v) = ?o |- _ => rewrite to_of_val in H
| H: is_val ?e |- _ => destruct (proj1 (is_val_spec e) H) as (? & ?); clear H
end.
(* Misc *)
Lemma is_val_of_val v : is_val (of_val v).
Proof. apply is_val_spec. rewrite to_of_val. eauto. Qed.
(* literals and our operators have decidable equality. *)
Global Instance base_lit_eq_dec : EqDecision base_lit.
Proof. solve_decision. Defined.
Global Instance un_op_eq_dec : EqDecision un_op.
Proof. solve_decision. Defined.
Global Instance bin_op_eq_dec : EqDecision bin_op.
Proof. solve_decision. Defined.
(** Substitution *)
Fixpoint subst (x : string) (es : expr) (e : expr) : expr :=
match e with
| Lit _ => e
| Var y => if decide (x = y) then es else Var y
| Lam y e =>
Lam y $ if decide (BNamed x = y) then e else subst x es e
| App e1 e2 => App (subst x es e1) (subst x es e2)
| TApp e => TApp (subst x es e)
| TLam e => TLam (subst x es e)
| Pack e => Pack (subst x es e)
| Unpack y e1 e2 => Unpack y (subst x es e1) (if decide (BNamed x = y) then e2 else subst x es e2)
| UnOp op e => UnOp op (subst x es e)
| BinOp op e1 e2 => BinOp op (subst x es e1) (subst x es e2)
| If e0 e1 e2 => If (subst x es e0) (subst x es e1) (subst x es e2)
| Pair e1 e2 => Pair (subst x es e1) (subst x es e2)
| Fst e => Fst (subst x es e)
| Snd e => Snd (subst x es e)
| InjL e => InjL (subst x es e)
| InjR e => InjR (subst x es e)
| Case e0 e1 e2 => Case (subst x es e0) (subst x es e1) (subst x es e2)
end.
Definition subst' (mx : binder) (es : expr) : expr expr :=
match mx with BNamed x => subst x es | BAnon => id end.
(** The stepping relation *)
Definition un_op_eval (op : un_op) (v : val) : option val :=
match op, v with
| NegOp, LitV (LitBool b) => Some $ LitV $ LitBool (negb b)
| MinusUnOp, LitV (LitInt n) => Some $ LitV $ LitInt (- n)
| _, _ => None
end.
Definition bin_op_eval_int (op : bin_op) (n1 n2 : Z) : option base_lit :=
match op with
| PlusOp => Some $ LitInt (n1 + n2)
| MinusOp => Some $ LitInt (n1 - n2)
| MultOp => Some $ LitInt (n1 * n2)
| LtOp => Some $ LitBool (bool_decide (n1 < n2))
| LeOp => Some $ LitBool (bool_decide (n1 n2))
| EqOp => Some $ LitBool (bool_decide (n1 = n2))
end%Z.
Definition bin_op_eval (op : bin_op) (v1 v2 : val) : option val :=
match v1, v2 with
| LitV (LitInt n1), LitV (LitInt n2) => LitV <$> bin_op_eval_int op n1 n2
| _, _ => None
end.
Inductive base_step : expr expr Prop :=
| BetaS x e1 e2 e' :
is_val e2
e' = subst' x e2 e1
base_step (App (Lam x e1) e2) e'
| TBetaS e1 :
base_step (TApp (TLam e1)) e1
| UnpackS e1 e2 e' x :
is_val e1
e' = subst' x e1 e2
base_step (Unpack x (Pack e1) e2) e'
| UnOpS op e v v' :
to_val e = Some v
un_op_eval op v = Some v'
base_step (UnOp op e) (of_val v')
| BinOpS op e1 v1 e2 v2 v' :
to_val e1 = Some v1
to_val e2 = Some v2
bin_op_eval op v1 v2 = Some v'
base_step (BinOp op e1 e2) (of_val v')
| IfTrueS e1 e2 :
base_step (If (Lit $ LitBool true) e1 e2) e1
| IfFalseS e1 e2 :
base_step (If (Lit $ LitBool false) e1 e2) e2
| FstS e1 e2 :
is_val e1
is_val e2
base_step (Fst (Pair e1 e2)) e1
| SndS e1 e2 :
is_val e1
is_val e2
base_step (Snd (Pair e1 e2)) e2
| CaseLS e e1 e2 :
is_val e
base_step (Case (InjL e) e1 e2) (App e1 e)
| CaseRS e e1 e2 :
is_val e
base_step (Case (InjR e) e1 e2) (App e2 e)
.
(** We define evaluation contexts *)
Inductive ectx :=
| HoleCtx
| AppLCtx (K: ectx) (v2 : val)
| AppRCtx (e1 : expr) (K: ectx)
| TAppCtx (K: ectx)
| PackCtx (K: ectx)
| UnpackCtx (x : binder)(K: ectx) (e2 : expr)
| UnOpCtx (op : un_op) (K: ectx)
| BinOpLCtx (op : bin_op) (K: ectx) (v2 : val)
| BinOpRCtx (op : bin_op) (e1 : expr) (K: ectx)
| IfCtx (K: ectx) (e1 e2 : expr)
| PairLCtx (K: ectx) (v2 : val)
| PairRCtx (e1 : expr) (K: ectx)
| FstCtx (K: ectx)
| SndCtx (K: ectx)
| InjLCtx (K: ectx)
| InjRCtx (K: ectx)
| CaseCtx (K: ectx) (e1 : expr) (e2 : expr) .
Fixpoint fill (K : ectx) (e : expr) : expr :=
match K with
| HoleCtx => e
| AppLCtx K v2 => App (fill K e) (of_val v2)
| AppRCtx e1 K => App e1 (fill K e)
| TAppCtx K => TApp (fill K e)
| PackCtx K => Pack (fill K e)
| UnpackCtx x K e2 => Unpack x (fill K e) e2
| UnOpCtx op K => UnOp op (fill K e)
| BinOpLCtx op K v2 => BinOp op (fill K e) (of_val v2)
| BinOpRCtx op e1 K => BinOp op e1 (fill K e)
| IfCtx K e1 e2 => If (fill K e) e1 e2
| PairLCtx K v2 => Pair (fill K e) (of_val v2)
| PairRCtx e1 K => Pair e1 (fill K e)
| FstCtx K => Fst (fill K e)
| SndCtx K => Snd (fill K e)
| InjLCtx K => InjL (fill K e)
| InjRCtx K => InjR (fill K e)
| CaseCtx K e1 e2 => Case (fill K e) e1 e2
end.
Fixpoint comp_ectx (K: ectx) (K' : ectx) : ectx :=
match K with
| HoleCtx => K'
| AppLCtx K v2 => AppLCtx (comp_ectx K K') v2
| AppRCtx e1 K => AppRCtx e1 (comp_ectx K K')
| TAppCtx K => TAppCtx (comp_ectx K K')
| PackCtx K => PackCtx (comp_ectx K K')
| UnpackCtx x K e2 => UnpackCtx x (comp_ectx K K') e2
| UnOpCtx op K => UnOpCtx op (comp_ectx K K')
| BinOpLCtx op K v2 => BinOpLCtx op (comp_ectx K K') v2
| BinOpRCtx op e1 K => BinOpRCtx op e1 (comp_ectx K K')
| IfCtx K e1 e2 => IfCtx (comp_ectx K K') e1 e2
| PairLCtx K v2 => PairLCtx (comp_ectx K K') v2
| PairRCtx e1 K => PairRCtx e1 (comp_ectx K K')
| FstCtx K => FstCtx (comp_ectx K K')
| SndCtx K => SndCtx (comp_ectx K K')
| InjLCtx K => InjLCtx (comp_ectx K K')
| InjRCtx K => InjRCtx (comp_ectx K K')
| CaseCtx K e1 e2 => CaseCtx (comp_ectx K K') e1 e2
end.
(** Contextual steps *)
Inductive contextual_step (e1 : expr) (e2 : expr) : Prop :=
Ectx_step K e1' e2' :
e1 = fill K e1' e2 = fill K e2'
base_step e1' e2' contextual_step e1 e2.
Definition reducible (e : expr) :=
e', contextual_step e e'.
Definition empty_ectx := HoleCtx.
(** Basic properties about the language *)
Lemma fill_empty e : fill empty_ectx e = e.
Proof. done. Qed.
Lemma fill_comp (K1 K2 : ectx) e : fill K1 (fill K2 e) = fill (comp_ectx K1 K2) e.
Proof. induction K1; simpl; congruence. Qed.
Lemma base_contextual_step e1 e2 :
base_step e1 e2 contextual_step e1 e2.
Proof. apply Ectx_step with empty_ectx; by rewrite ?fill_empty. Qed.
Lemma fill_contextual_step K e1 e2 :
contextual_step e1 e2 contextual_step (fill K e1) (fill K e2).
Proof.
destruct 1 as [K' e1' e2' -> ->].
rewrite !fill_comp. by econstructor.
Qed.
Fixpoint is_closed (X : list string) (e : expr) : bool :=
match e with
| Var x => bool_decide (x X)
| Lam x e => is_closed (x :b: X) e
| Unpack x e1 e2 => is_closed X e1 && is_closed (x :b: X) e2
| Lit _ => true
| UnOp _ e | Fst e | Snd e | InjL e | InjR e | TApp e | TLam e | Pack e => is_closed X e
| App e1 e2 | BinOp _ e1 e2 | Pair e1 e2 => is_closed X e1 && is_closed X e2
| If e0 e1 e2 | Case e0 e1 e2 =>
is_closed X e0 && is_closed X e1 && is_closed X e2
end.
(** [closed] states closedness as a Coq proposition, through the [Is_true] transformer. *)
Definition closed (X : list string) (e : expr) : Prop := Is_true (is_closed X e).
#[export] Instance closed_proof_irrel X e : ProofIrrel (closed X e).
Proof. unfold closed. apply _. Qed.
#[export] Instance closed_dec X e : Decision (closed X e).
Proof. unfold closed. apply _. Defined.
(** closed expressions *)
Lemma is_closed_weaken X Y e : is_closed X e X Y is_closed Y e.
Proof. revert X Y; induction e; naive_solver (eauto; set_solver). Qed.
Lemma is_closed_weaken_nil X e : is_closed [] e is_closed X e.
Proof. intros. by apply is_closed_weaken with [], list_subseteq_nil. Qed.
Lemma is_closed_subst X e x es :
is_closed [] es is_closed (x :: X) e is_closed X (subst x es e).
Proof.
intros ?.
induction e in X |-*; simpl; intros ?; destruct_and?; split_and?; simplify_option_eq;
try match goal with
| H : ¬(_ _) |- _ => apply not_and_l in H as [?%dec_stable|?%dec_stable]
end; eauto using is_closed_weaken with set_solver.
Qed.
Lemma is_closed_do_subst' X e x es :
is_closed [] es is_closed (x :b: X) e is_closed X (subst' x es e).
Proof. destruct x; eauto using is_closed_subst. Qed.
(** Substitution lemmas *)
Lemma subst_is_closed X e x es : is_closed X e x X subst x es e = e.
Proof.
induction e in X |-*; simpl; rewrite ?bool_decide_spec, ?andb_True; intros ??;
repeat case_decide; simplify_eq; simpl; f_equal; intuition eauto with set_solver.
Qed.
Lemma subst_is_closed_nil e x es : is_closed [] e subst x es e = e.
Proof. intros. apply subst_is_closed with []; set_solver. Qed.
Lemma subst'_is_closed_nil e x es : is_closed [] e subst' x es e = e.
Proof. intros. destruct x as [ | x]. { done. } by apply subst_is_closed_nil. Qed.
(* we derive a few lemmas about contextual steps *)
Lemma contextual_step_app_l e1 e1' e2:
is_val e2
contextual_step e1 e1'
contextual_step (App e1 e2) (App e1' e2).
Proof.
intros [v <-%of_to_val]%is_val_spec Hcontextual.
by eapply (fill_contextual_step (AppLCtx HoleCtx v)).
Qed.
Lemma contextual_step_app_r e1 e2 e2':
contextual_step e2 e2'
contextual_step (App e1 e2) (App e1 e2').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (AppRCtx e1 HoleCtx)).
Qed.
Lemma contextual_step_tapp e e':
contextual_step e e'
contextual_step (TApp e) (TApp e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (TAppCtx HoleCtx)).
Qed.
Lemma contextual_step_pack e e':
contextual_step e e'
contextual_step (Pack e) (Pack e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (PackCtx HoleCtx)).
Qed.
Lemma contextual_step_unpack x e e' e2:
contextual_step e e'
contextual_step (Unpack x e e2) (Unpack x e' e2).
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (UnpackCtx x HoleCtx e2)).
Qed.
Lemma contextual_step_unop op e e':
contextual_step e e'
contextual_step (UnOp op e) (UnOp op e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (UnOpCtx op HoleCtx)).
Qed.
Lemma contextual_step_binop_l op e1 e1' e2:
is_val e2
contextual_step e1 e1'
contextual_step (BinOp op e1 e2) (BinOp op e1' e2).
Proof.
intros [v <-%of_to_val]%is_val_spec Hcontextual.
by eapply (fill_contextual_step (BinOpLCtx op HoleCtx v)).
Qed.
Lemma contextual_step_binop_r op e1 e2 e2':
contextual_step e2 e2'
contextual_step (BinOp op e1 e2) (BinOp op e1 e2').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (BinOpRCtx op e1 HoleCtx)).
Qed.
Lemma contextual_step_if e e' e1 e2:
contextual_step e e'
contextual_step (If e e1 e2) (If e' e1 e2).
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (IfCtx HoleCtx e1 e2)).
Qed.
Lemma contextual_step_pair_l e1 e1' e2:
is_val e2
contextual_step e1 e1'
contextual_step (Pair e1 e2) (Pair e1' e2).
Proof.
intros [v <-%of_to_val]%is_val_spec Hcontextual.
by eapply (fill_contextual_step (PairLCtx HoleCtx v)).
Qed.
Lemma contextual_step_pair_r e1 e2 e2':
contextual_step e2 e2'
contextual_step (Pair e1 e2) (Pair e1 e2').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (PairRCtx e1 HoleCtx)).
Qed.
Lemma contextual_step_fst e e':
contextual_step e e'
contextual_step (Fst e) (Fst e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (FstCtx HoleCtx)).
Qed.
Lemma contextual_step_snd e e':
contextual_step e e'
contextual_step (Snd e) (Snd e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (SndCtx HoleCtx)).
Qed.
Lemma contextual_step_injl e e':
contextual_step e e'
contextual_step (InjL e) (InjL e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (InjLCtx HoleCtx)).
Qed.
Lemma contextual_step_injr e e':
contextual_step e e'
contextual_step (InjR e) (InjR e').
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (InjRCtx HoleCtx)).
Qed.
Lemma contextual_step_case e e' e1 e2:
contextual_step e e'
contextual_step (Case e e1 e2) (Case e' e1 e2).
Proof.
intros Hcontextual.
by eapply (fill_contextual_step (CaseCtx HoleCtx e1 e2)).
Qed.
#[export]
Hint Resolve
contextual_step_app_l contextual_step_app_r contextual_step_binop_l contextual_step_binop_r
contextual_step_case contextual_step_fst contextual_step_if contextual_step_injl contextual_step_injr
contextual_step_pack contextual_step_pair_l contextual_step_pair_r contextual_step_snd contextual_step_tapp
contextual_step_tapp contextual_step_unop contextual_step_unpack : core.