282 lines
8.6 KiB
Coq
282 lines
8.6 KiB
Coq
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From Coq Require Import Strings.String.
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From Coq Require Import Lists.List.
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Import ListNotations.
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Require Import terms.
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Inductive type_DeBruijn : Type :=
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| ty_id : string -> type_DeBruijn
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| ty_fvar : string -> type_DeBruijn
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| ty_bvar : nat -> type_DeBruijn
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| ty_univ : type_DeBruijn -> type_DeBruijn
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| ty_spec : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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| ty_func : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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| ty_morph : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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| ty_ladder : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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.
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Inductive expr_DeBruijn : Type :=
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| ex_var : nat -> expr_DeBruijn
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| ex_ty_abs : expr_DeBruijn -> expr_DeBruijn
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| ex_ty_app : expr_DeBruijn -> type_DeBruijn -> expr_DeBruijn
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| ex_abs : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_morph : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_app : expr_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| varlet : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_ascend : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_descend : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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.
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(* get the list of all free variables in a type term *)
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Fixpoint type_fv (τ : type_DeBruijn) {struct τ} : (list string) :=
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match τ with
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| ty_id s => []
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| ty_fvar α => [α]
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| ty_bvar x => []
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| ty_univ τ => (type_fv τ)
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| ty_spec σ τ => (type_fv σ) ++ (type_fv τ)
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| ty_func σ τ => (type_fv σ) ++ (type_fv τ)
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| ty_morph σ τ => (type_fv σ) ++ (type_fv τ)
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| ty_ladder σ τ => (type_fv σ) ++ (type_fv τ)
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end.
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(* substitute free variable x with type σ in τ *)
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Fixpoint subst_type (x:string) (σ:type_DeBruijn) (τ:type_DeBruijn) {struct τ} : type_DeBruijn :=
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match τ with
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| ty_id s => ty_id s
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| ty_fvar s => if eqb x s then σ else τ
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| ty_bvar y => ty_bvar y
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| ty_univ τ => ty_univ (subst_type x σ τ)
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| ty_spec τ1 τ2 => ty_spec (subst_type x σ τ1) (subst_type x σ τ2)
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| ty_func τ1 τ2 => ty_func (subst_type x σ τ1) (subst_type x σ τ2)
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| ty_morph τ1 τ2 => ty_morph (subst_type x σ τ1) (subst_type x σ τ2)
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| ty_ladder τ1 τ2 => ty_ladder (subst_type x σ τ1) (subst_type x σ τ2)
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end.
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(* replace a free variable with a new (dangling) bound variable *)
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Fixpoint type_bind_fvar (x:string) (n:nat) (τ:type_DeBruijn) {struct τ} : type_DeBruijn :=
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match τ with
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| ty_id s => ty_id s
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| ty_fvar s => if eqb x s then ty_bvar n else τ
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| ty_bvar n => ty_bvar n
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| ty_univ τ1 => ty_univ (type_bind_fvar x (S n) τ1)
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| ty_spec τ1 τ2 => ty_spec (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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| ty_func τ1 τ2 => ty_func (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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| ty_morph τ1 τ2 => ty_morph (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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| ty_ladder τ1 τ2 => ty_ladder (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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end.
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(* replace (dangling) index with another type *)
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Fixpoint type_open_rec (k:nat) (σ:type_DeBruijn) (τ:type_DeBruijn) {struct τ} : type_DeBruijn :=
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match τ with
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| ty_id s => ty_id s
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| ty_fvar s => ty_fvar s
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| ty_bvar i => if Nat.eqb k i then σ else τ
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| ty_univ τ1 => ty_univ (type_open_rec (S k) σ τ1)
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| ty_spec τ1 τ2 => ty_spec (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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| ty_func τ1 τ2 => ty_func (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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| ty_morph τ1 τ2 => ty_morph (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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| ty_ladder τ1 τ2 => ty_ladder (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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end.
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Notation "'[' z '~>' u ']' e" := (subst_type z u e) (at level 68).
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Notation "'{' k '~>' σ '}' τ" := (type_open_rec k σ τ) (at level 67).
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Definition type_open σ τ := type_open_rec 0 σ τ.
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(* is the type locally closed ? *)
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Inductive type_lc : type_DeBruijn -> Prop :=
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| Tlc_Id : forall s, type_lc (ty_id s)
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| Tlc_Var : forall s, type_lc (ty_fvar s)
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| Tlc_Univ : forall τ1 L,
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(forall x, ~ (In x L) -> type_lc (type_open (ty_fvar x) τ1)) ->
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type_lc (ty_univ τ1)
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| Tlc_Spec : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_spec τ1 τ2)
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| Tlc_Func : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_func τ1 τ2)
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| Tlc_Morph : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_morph τ1 τ2)
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| Tlc_Ladder : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_ladder τ1 τ2)
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.
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(* number of abstractions *)
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Fixpoint type_debruijn_depth (τ:type_DeBruijn) : nat :=
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match τ with
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| ty_id s => 0
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| ty_fvar s => 0
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| ty_bvar x => 0
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| ty_func s t => max (type_debruijn_depth s) (type_debruijn_depth t)
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| ty_morph s t => max (type_debruijn_depth s) (type_debruijn_depth t)
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| ty_univ t => (1 + (type_debruijn_depth t))
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| ty_spec s t => ((type_debruijn_depth s) - 1)
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| ty_ladder s t => max (type_debruijn_depth s) (type_debruijn_depth t)
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end.
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Fixpoint type_named2debruijn (τ:type_term) {struct τ} : type_DeBruijn :=
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match τ with
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| type_id s => ty_id s
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| type_var s => ty_fvar s
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| type_univ x t => let t':=(type_named2debruijn t) in (ty_univ (type_bind_fvar x 0 t'))
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| type_spec s t => ty_spec (type_named2debruijn s) (type_named2debruijn t)
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| type_fun s t => ty_func (type_named2debruijn s) (type_named2debruijn t)
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| type_morph s t => ty_morph (type_named2debruijn s) (type_named2debruijn t)
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| type_ladder s t => ty_ladder (type_named2debruijn s) (type_named2debruijn t)
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end.
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Coercion type_named2debruijn : type_term >-> type_DeBruijn.
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Lemma list_in_tail : forall x (E:list string) f,
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In x E ->
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In x (cons f E).
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Proof.
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intros.
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simpl.
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right.
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apply H.
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Qed.
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Lemma list_in_concatA : forall x (E:list string) (F:list string),
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In x E ->
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In x (E ++ F).
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Proof.
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Admitted.
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Lemma list_in_concatB : forall x (E:list string) (F:list string),
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In x F ->
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In x (E ++ F).
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Proof.
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intros.
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induction E.
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auto.
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apply list_in_tail.
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Admitted.
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Lemma list_notin_singleton : forall (x:string) (y:string),
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((eqb x y) = false) -> ~ In x [ y ].
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Proof.
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Admitted.
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Lemma list_elim_notin_singleton : forall (x:string) (y:string),
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~ In x [y] -> ((eqb x y) = false).
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Proof.
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Admitted.
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Lemma subst_fresh_type : forall (x : string) (τ:type_DeBruijn) (σ:type_DeBruijn),
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~(In x (type_fv τ)) ->
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(subst_type x σ τ) = τ
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.
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Proof.
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intros.
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induction τ.
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- reflexivity.
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- unfold type_fv in H.
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apply list_elim_notin_singleton in H.
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simpl.
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case_eq (x =? s)%string.
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congruence.
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reflexivity.
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- reflexivity.
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- simpl. rewrite IHτ.
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reflexivity.
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apply H.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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simpl type_fv in H.
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contradict H. apply list_in_concatB, H.
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contradict H. apply list_in_concatA, H.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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contradict H. apply list_in_concatB, H.
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contradict H. apply list_in_concatA, H.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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contradict H. apply list_in_concatB, H.
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contradict H. apply list_in_concatA, H.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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contradict H. apply list_in_concatB, H.
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contradict H. apply list_in_concatA, H.
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Qed.
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Lemma open_rec_lc_core : forall τ j σ1 i σ2,
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i <> j ->
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{j ~> σ1} τ = {i ~> σ2} ({j ~> σ1} τ) ->
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τ = {i ~> σ1} τ.
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Proof with (eauto with *).
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induction τ;
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intros j v i u Neq H;
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simpl in *; try solve [inversion H; f_equal; eauto].
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(* case (ty_bvar).*)
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destruct (Nat.eqb j n)...
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destruct (Nat.eqb i n)...
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Admitted.
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Lemma type_open_rec_lc : forall k σ τ,
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type_lc τ ->
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{ k ~> σ } τ = τ.
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Proof.
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intros.
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generalize dependent k.
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induction H.
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- auto.
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- auto.
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- intro k.
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unfold type_open in *.
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(*
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pick fresh x for L.
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apply open_rec_lc_core with (i := S k) (j := 0) (u := u) (v := x). auto. auto.
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*)
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admit.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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Admitted.
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Lemma type_subst_open_rec : forall τ1 τ2 σ x k,
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type_lc σ ->
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[x ~> σ] ({k ~> τ2} τ1) = {k ~> [x ~> σ] τ2} ([x ~> σ] τ1).
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Proof.
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intros.
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induction τ1.
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(* id *)
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- auto.
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(* free var *)
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- simpl.
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case_eq (eqb x s).
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intro.
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apply eq_sym.
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apply type_open_rec_lc, H.
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auto.
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(* bound var *)
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- simpl.
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case_eq (Nat.eqb k n).
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auto.
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auto.
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(* univ *)
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- simpl.
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admit.
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- simpl. rewrite IHτ1_1. rewrite IHτ1_2. reflexivity.
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- simpl. rewrite IHτ1_1. rewrite IHτ1_2. reflexivity.
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- simpl. rewrite IHτ1_1. rewrite IHτ1_2. reflexivity.
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- simpl. rewrite IHτ1_1. rewrite IHτ1_2. reflexivity.
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Admitted.
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