Library Coq.Init.Datatypes


Set Implicit Arguments.

Require Import Notations.
Require Import Logic.

Datatypes with zero and one element

Empty_set is a datatype with no inhabitant

Inductive Empty_set : Set :=.

unit is a singleton datatype with sole inhabitant tt

Inductive unit : Set :=
    tt : unit.

The boolean datatype

bool is the datatype of the boolean values true and false

Inductive bool : Set :=
  | true : bool
  | false : bool.

Add Printing If bool.

Delimit Scope bool_scope with bool.


Basic boolean operators

Definition andb (b1 b2:bool) : bool := if b1 then b2 else false.

Definition orb (b1 b2:bool) : bool := if b1 then true else b2.

Definition implb (b1 b2:bool) : bool := if b1 then b2 else true.

Definition xorb (b1 b2:bool) : bool :=
  match b1, b2 with
    | true, true => false
    | true, false => true
    | false, true => true
    | false, false => false
  end.

Definition negb (b:bool) := if b then false else true.

Infix "||" := orb : bool_scope.
Infix "&&" := andb : bool_scope.

Basic properties of andb

Lemma andb_prop : forall a b:bool, andb a b = true -> a = true /\ b = true.
Hint Resolve andb_prop: bool.

Lemma andb_true_intro :
  forall b1 b2:bool, b1 = true /\ b2 = true -> andb b1 b2 = true.
Hint Resolve andb_true_intro: bool.

Interpretation of booleans as propositions

Inductive eq_true : bool -> Prop := is_eq_true : eq_true true.

Hint Constructors eq_true : eq_true.

Another way of interpreting booleans as propositions

Definition is_true b := b = true.

is_true can be activated as a coercion by (Local) Coercion is_true : bool >-> Prop.
Additional rewriting lemmas about eq_true

Lemma eq_true_ind_r :
  forall (P : bool -> Prop) (b : bool), P b -> eq_true b -> P true.

Lemma eq_true_rec_r :
  forall (P : bool -> Set) (b : bool), P b -> eq_true b -> P true.

Lemma eq_true_rect_r :
  forall (P : bool -> Type) (b : bool), P b -> eq_true b -> P true.

The BoolSpec inductive will be used to relate a boolean value and two propositions corresponding respectively to the true case and the false case. Interest: BoolSpec behave nicely with case and destruct. See also Bool.reflect when Q = ~P.

Inductive BoolSpec (P Q : Prop) : bool -> Prop :=
  | BoolSpecT : P -> BoolSpec P Q true
  | BoolSpecF : Q -> BoolSpec P Q false.
Hint Constructors BoolSpec.

Peano natural numbers

nat is the datatype of natural numbers built from O and successor S; note that the constructor name is the letter O. Numbers in nat can be denoted using a decimal notation; e.g. 3%nat abbreviates S (S (S O))

Inductive nat : Set :=
  | O : nat
  | S : nat -> nat.

Delimit Scope nat_scope with nat.

Container datatypes

option A is the extension of A with an extra element None

Inductive option (A:Type) : Type :=
  | Some : A -> option A
  | None : option A.


Definition option_map (A B:Type) (f:A->B) o :=
  match o with
    | Some a => Some (f a)
    | None => None
  end.

sum A B, written A + B, is the disjoint sum of A and B

Inductive sum (A B:Type) : Type :=
  | inl : A -> sum A B
  | inr : B -> sum A B.

Notation "x + y" := (sum x y) : type_scope.


prod A B, written A * B, is the product of A and B; the pair pair A B a b of a and b is abbreviated (a,b)

Inductive prod (A B:Type) : Type :=
  pair : A -> B -> prod A B.

Add Printing Let prod.

Notation "x * y" := (prod x y) : type_scope.
Notation "( x , y , .. , z )" := (pair .. (pair x y) .. z) : core_scope.


Section projections.
  Variables A B : Type.
  Definition fst (p:A * B) := match p with
                                | (x, y) => x
                              end.
  Definition snd (p:A * B) := match p with
                                | (x, y) => y
                              end.
End projections.

Hint Resolve pair inl inr: core.

Lemma surjective_pairing :
  forall (A B:Type) (p:A * B), p = pair (fst p) (snd p).

Lemma injective_projections :
  forall (A B:Type) (p1 p2:A * B),
    fst p1 = fst p2 -> snd p1 = snd p2 -> p1 = p2.

Definition prod_uncurry (A B C:Type) (f:prod A B -> C)
  (x:A) (y:B) : C := f (pair x y).

Definition prod_curry (A B C:Type) (f:A -> B -> C)
  (p:prod A B) : C := match p with
                       | pair x y => f x y
                       end.

Polymorphic lists and some operations

Inductive list (A : Type) : Type :=
 | nil : list A
 | cons : A -> list A -> list A.

Infix "::" := cons (at level 60, right associativity) : list_scope.
Delimit Scope list_scope with list.

Local Open Scope list_scope.

Definition length (A : Type) : list A -> nat :=
  fix length l :=
  match l with
   | nil => O
   | _ :: l' => S (length l')
  end.

Concatenation of two lists

Definition app (A : Type) : list A -> list A -> list A :=
  fix app l m :=
  match l with
   | nil => m
   | a :: l1 => a :: app l1 m
  end.

Infix "++" := app (right associativity, at level 60) : list_scope.

The comparison datatype


Inductive comparison : Set :=
  | Eq : comparison
  | Lt : comparison
  | Gt : comparison.

Definition CompOpp (r:comparison) :=
  match r with
    | Eq => Eq
    | Lt => Gt
    | Gt => Lt
  end.

Lemma CompOpp_involutive : forall c, CompOpp (CompOpp c) = c.

Lemma CompOpp_inj : forall c c', CompOpp c = CompOpp c' -> c = c'.

Lemma CompOpp_iff : forall c c', CompOpp c = c' <-> c = CompOpp c'.

The CompareSpec inductive relates a comparison value with three propositions, one for each possible case. Typically, it can be used to specify a comparison function via some equality and order predicates. Interest: CompareSpec behave nicely with case and destruct.

Inductive CompareSpec (Peq Plt Pgt : Prop) : comparison -> Prop :=
 | CompEq : Peq -> CompareSpec Peq Plt Pgt Eq
 | CompLt : Plt -> CompareSpec Peq Plt Pgt Lt
 | CompGt : Pgt -> CompareSpec Peq Plt Pgt Gt.
Hint Constructors CompareSpec.

For having clean interfaces after extraction, CompareSpec is declared in Prop. For some situations, it is nonetheless useful to have a version in Type. Interestingly, these two versions are equivalent.

Inductive CompareSpecT (Peq Plt Pgt : Prop) : comparison -> Type :=
 | CompEqT : Peq -> CompareSpecT Peq Plt Pgt Eq
 | CompLtT : Plt -> CompareSpecT Peq Plt Pgt Lt
 | CompGtT : Pgt -> CompareSpecT Peq Plt Pgt Gt.
Hint Constructors CompareSpecT.

Lemma CompareSpec2Type : forall Peq Plt Pgt c,
 CompareSpec Peq Plt Pgt c -> CompareSpecT Peq Plt Pgt c.

As an alternate formulation, one may also directly refer to predicates eq and lt for specifying a comparison, rather that fully-applied propositions. This CompSpec is now a particular case of CompareSpec.

Definition CompSpec {A} (eq lt : A->A->Prop)(x y:A) : comparison -> Prop :=
 CompareSpec (eq x y) (lt x y) (lt y x).
Definition CompSpecT {A} (eq lt : A->A->Prop)(x y:A) : comparison -> Type :=
 CompareSpecT (eq x y) (lt x y) (lt y x).
Hint Unfold CompSpec CompSpecT.

Lemma CompSpec2Type : forall A (eq lt:A->A->Prop) x y c,
 CompSpec eq lt x y c -> CompSpecT eq lt x y c.

Misc Other Datatypes

identity A a is the family of datatypes on A whose sole non-empty member is the singleton datatype identity A a a whose sole inhabitant is denoted refl_identity A a

Inductive identity (A:Type) (a:A) : A -> Type :=
  identity_refl : identity a a.
Hint Resolve identity_refl: core.


Identity type

Definition ID := forall A:Type, A -> A.
Definition id : ID := fun A x => x.