Hash sets

This module develops the type Std.Data.HashSet of dependent hash sets.

Lemmas about the operations on Std.Data.HashSet are available in the module Std.Data.HashSet.Lemmas.

See the module Std.Data.HashSet.Raw for a variant of this type which is safe to use in nested inductive types.

structure Std.HashSet (α : Type u) [BEq α] [Hashable α] : Type u

Hash sets.

This is a simple separate-chaining hash table. The data of the hash set consists of a cached size and an array of buckets, where each bucket is a linked list of keys. The number of buckets is always a power of two. The hash set doubles its size upon inserting an element such that the number of elements is more than 75% of the number of buckets.

The hash table is backed by an Array. Users should make sure that the hash set is used linearly to avoid expensive copies.

The hash set uses == (provided by the BEq typeclass) to compare elements and hash (provided by the Hashable typeclass) to hash them. To ensure that the operations behave as expected, == should be an equivalence relation and a == b should imply hash a = hash b (see also the EquivBEq and LawfulHashable typeclasses). Both of these conditions are automatic if the BEq instance is lawful, i.e., if a == b implies a = b.

These hash sets contain a bundled well-formedness invariant, which means that they cannot be used in nested inductive types. For these use cases, Std.Data.HashSet.Raw and Std.Data.HashSet.Raw.WF unbundle the invariant from the hash set. When in doubt, prefer HashSet over HashSet.Raw.

• inner : Std.HashMap α Unit

  Internal implementation detail of the hash set.

@[inline]

def Std.HashSet.empty {α : Type u} [BEq α] [Hashable α] (capacity : optParam Nat 8) : Std.HashSet α

Creates a new empty hash set. The optional parameter capacity can be supplied to presize the set so that it can hold the given number of elements without reallocating. It is also possible to use the empty collection notations ∅ and {} to create an empty hash set with the default capacity.

Equations

• Std.HashSet.empty capacity = { inner := Std.HashMap.empty capacity }

instance Std.HashSet.instEmptyCollection {α : Type u} [BEq α] [Hashable α] : EmptyCollection (Std.HashSet α)

Equations

• Std.HashSet.instEmptyCollection = { emptyCollection := Std.HashSet.empty }

instance Std.HashSet.instInhabited {α : Type u} [BEq α] [Hashable α] : Inhabited (Std.HashSet α)

Equations

• Std.HashSet.instInhabited = { default := ∅ }

@[inline]

def Std.HashSet.insert {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → α → Std.HashSet α

Inserts the given element into the set. If the hash set already contains an element that is equal (with regard to ==) to the given element, then the hash set is returned unchanged.

Equations

• m.insert a = { inner := m.inner.insertIfNew a () }

@[inline]

def Std.HashSet.containsThenInsert {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → α → Bool × Std.HashSet α

Checks whether an element is present in a set and inserts the element if it was not found. If the hash set already contains an element that is equal (with regard to ==) to the given element, then the hash set is returned unchanged.

Equivalent to (but potentially faster than) calling contains followed by insert.

Equations

• m.containsThenInsert a = match m.inner.containsThenInsertIfNew a () with | (replaced, r) => (replaced, { inner := r })

@[inline]

def Std.HashSet.contains {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → α → Bool

Returns true if the given key is present in the set. There is also a Prop-valued version of this: a ∈ m is equivalent to m.contains a = true.

Observe that this is different behavior than for lists: for lists, ∈ uses = and contains use == for comparisons, while for hash sets, both use ==.

Equations

• m.contains a = m.inner.contains a

instance Std.HashSet.instMembership {α : Type u} [BEq α] [Hashable α] : Membership α (Std.HashSet α)

Equations

• Std.HashSet.instMembership = { mem := fun (a : α) (m : Std.HashSet α) => a ∈ m.inner }

instance Std.HashSet.instDecidableMem {α : Type u} [BEq α] [Hashable α] {m : Std.HashSet α} {a : α} : Decidable (a ∈ m)

Equations

• Std.HashSet.instDecidableMem = inferInstanceAs (Decidable (a ∈ m.inner))

@[inline]

def Std.HashSet.erase {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → α → Std.HashSet α

Removes the element if it exists.

Equations

• m.erase a = { inner := m.inner.erase a }

@[inline]

def Std.HashSet.size {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → Nat

The number of elements present in the set

Equations

• m.size = m.inner.size

@[inline]

def Std.HashSet.isEmpty {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → Bool

Returns true if the hash set contains no elements.

Note that if your BEq instance is not reflexive or your Hashable instance is not lawful, then it is possible that this function returns false even though m.contains a = false for all a.

Equations

• m.isEmpty = m.inner.isEmpty

We currently do not provide lemmas for the functions below.

@[inline]

def Std.HashSet.filter {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → (α → Bool) → Std.HashSet α → Std.HashSet α

Removes all elements from the hash set for which the given function returns false.

Equations

• Std.HashSet.filter f m = { inner := Std.HashMap.filter (fun (a : α) (x : Unit) => f a) m.inner }

@[inline]

def Std.HashSet.foldM {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → {m : Type v → Type v} → [inst : Monad m] → {β : Type v} → (β → α → m β) → β → Std.HashSet α → m β

Monadically computes a value by folding the given function over the elements in the hash set in some order.

Equations

• Std.HashSet.foldM f init b = Std.HashMap.foldM (fun (b : β) (a : α) (x : Unit) => f b a) init b.inner

@[inline]

def Std.HashSet.fold {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → {β : Type v} → (β → α → β) → β → Std.HashSet α → β

Folds the given function over the elements of the hash set in some order.

Equations

• Std.HashSet.fold f init m = Std.HashMap.fold (fun (b : β) (a : α) (x : Unit) => f b a) init m.inner

@[inline]

def Std.HashSet.forM {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → {m : Type v → Type v} → [inst : Monad m] → (α → m PUnit) → Std.HashSet α → m PUnit

Carries out a monadic action on each element in the hash set in some order.

Equations

• Std.HashSet.forM f b = Std.HashMap.forM (fun (a : α) (x : Unit) => f a) b.inner

@[inline]

def Std.HashSet.forIn {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → {m : Type v → Type v} → [inst : Monad m] → {β : Type v} → (α → β → m (ForInStep β)) → β → Std.HashSet α → m β

Support for the for loop construct in do blocks.

Equations

• Std.HashSet.forIn f init b = Std.HashMap.forIn (fun (a : α) (x : Unit) (acc : β) => f a acc) init b.inner

instance Std.HashSet.instForM {α : Type u} [BEq α] [Hashable α] {m : Type v → Type v} : ForM m (Std.HashSet α) α

Equations

• Std.HashSet.instForM = { forM := fun [Monad m] (m_1 : Std.HashSet α) (f : α → m PUnit) => Std.HashSet.forM f m_1 }

instance Std.HashSet.instForIn {α : Type u} [BEq α] [Hashable α] {m : Type v → Type v} : ForIn m (Std.HashSet α) α

Equations

• Std.HashSet.instForIn = { forIn := fun {β : Type v} [Monad m] (m_1 : Std.HashSet α) (init : β) (f : α → β → m (ForInStep β)) => Std.HashSet.forIn f init m_1 }

@[inline]

def Std.HashSet.toList {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → List α

Transforms the hash set into a list of elements in some order.

Equations

• m.toList = m.inner.keys

@[inline]

def Std.HashSet.toArray {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → Array α

Transforms the hash set into an array of elements in some order.

Equations

• m.toArray = m.inner.keysArray

@[inline]

def Std.HashSet.insertMany {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → {ρ : Type v} → [inst : ForIn Id ρ α] → Std.HashSet α → ρ → Std.HashSet α

Inserts multiple elements into the hash set. Note that unlike repeatedly calling insert, if the collection contains multiple elements that are equal (with regard to ==), then the last element in the collection will be present in the returned hash set.

Equations

• m.insertMany l = { inner := m.inner.insertManyUnit l }

@[inline]

def Std.HashSet.ofList {α : Type u} [BEq α] [Hashable α] (l : List α) : Std.HashSet α

Creates a hash set from a list of elements. Note that unlike repeatedly calling insert, if the collection contains multiple elements that are equal (with regard to ==), then the last element in the collection will be present in the returned hash set.

Equations

• Std.HashSet.ofList l = { inner := Std.HashMap.unitOfList l }

def Std.HashSet.Internal.numBuckets {α : Type u} : {x : BEq α} → {x_1 : Hashable α} → Std.HashSet α → Nat

Returns the number of buckets in the internal representation of the hash set. This function may be useful for things like monitoring system health, but it should be considered an internal implementation detail.

Equations

• Std.HashSet.Internal.numBuckets m = Std.HashMap.Internal.numBuckets m.inner

instance Std.HashSet.instRepr {α : Type u} [BEq α] [Hashable α] [Repr α] : Repr (Std.HashSet α)

Equations

• Std.HashSet.instRepr = { reprPrec := fun (m : Std.HashSet α) (prec : Nat) => Repr.addAppParen (Std.Format.text "Std.HashSet.ofList " ++ reprArg m.toList) prec }