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import Foundation
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/// Foldable describes types that have the ability to be folded to a summary value.
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public protocol Foldable {
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/// Eagerly folds a value to a summary value from left to right.
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///
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/// - Parameters:
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/// - fa: Value to be folded.
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/// - b: Initial value for the folding process.
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/// - f: Folding function.
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/// - Returns: Summary value resulting from the folding process.
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static func foldLeft<A, B>(_ fa: Kind<Self, A>, _ b: B, _ f: @escaping (B, A) -> B) -> B
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/// Lazily folds a value to a summary value from right to left.
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///
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/// - Parameters:
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/// - fa: Value to be folded.
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/// - b: Initial value for the folding process.
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/// - f: Folding function.
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/// - Returns: Summary value resulting from the folding process.
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static func foldRight<A, B>(_ fa: Kind<Self, A>, _ b: Eval<B>, _ f: @escaping (A, Eval<B>) -> Eval<B>) -> Eval<B>
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}
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public extension Foldable {
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/// Folds a structure of values provided that its type has an instance of `Monoid`.
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///
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/// It uses the monoid empty value as initial value and the combination method for the fold.
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///
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/// - Parameter fa: Value to be folded.
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/// - Returns: Summary value resulting from the folding process.
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static func fold<A: Monoid>(_ fa : Kind<Self, A>) -> A {
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return foldLeft(fa, A.empty(), { acc, a in acc.combine(a) })
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}
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/// Reduces the elements of a structure down to a single value by applying the provided transformation and aggregation funtions in a left-associative manner.
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///
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/// - Parameters:
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/// - fa: Value to be folded.
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/// - f: Transforming function.
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/// - g: Folding function.
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/// - Returns: Optional summary value resulting from the folding process. It will be an `Option.none` if the structure is empty, or a value if not.
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static func reduceLeftToOption<A, B>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> B, _ g: @escaping (B, A) -> B) -> Option<B> {
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return Option.fix(foldLeft(fa, Option.empty, { option, a in
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Option.fix(option).fold(constant(Option.some(f(a))),
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{ b in Option.some(g(b, a)) })
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}))
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}
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/// Reduces the elements of a structure down to a single value by applying the provided transformation and aggregation functions in a right-associative manner.
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///
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/// - Parameters:
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/// - fa: Value to be folded.
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/// - f: Transforming function.
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/// - g: Folding function.
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/// - Returns: Optional summary value resulting from the folding process. It will be an `Option.none` if the structure is empty, or a value if not.
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static func reduceRightToOption<A, B>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> B, _ g: @escaping (A, Eval<B>) -> Eval<B>) -> Eval<Option<B>> {
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return Eval.fix(foldRight(fa, Eval.now(Option.empty), { a, lb in
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Eval.fix(Eval.fix(lb).flatMap({ option in
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Option.fix(option).fold({ Eval.later({ Option.some(f(a)) }) },
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{ b in Eval.fix(g(a, Eval.now(b)).map(Option.some)) })
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}))
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}).map { x in Option.fix(x) })
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}
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/// Reduces the elements of a structure down to a single value by applying the provided aggregation function in a left-associative manner.
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///
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/// - Parameters:
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/// - fa: Value to be folded.
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/// - f: Folding function.
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/// - Returns: Optional summary value resulting from the folding process.
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static func reduceLeftOption<A>(_ fa: Kind<Self, A>, _ f: @escaping (A, A) -> A) -> Option<A> {
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return reduceLeftToOption(fa, id, f)
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}
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/// Reduces the elements of a structure down to a single value by applying the provided aggregation function in a right-associative manner.
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///
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/// - Parameters:
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/// - fa: Value to be folded.
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/// - f: Folding function.
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/// - Returns: Optional summary value resulting from the folding process.
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static func reduceRightOption<A>(_ fa: Kind<Self, A>, _ f: @escaping (A, Eval<A>) -> Eval<A>) -> Eval<Option<A>> {
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return reduceRightToOption(fa, id, f)
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}
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/// Folds a structure of values provided that its type has an instance of `Monoid`.
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///
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/// It uses the monoid empty value as initial value and the combination method for the fold.
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///
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/// - Parameter fa: Value to be folded.
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/// - Returns: Summary value resulting from the folding process.
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static func combineAll<A: Monoid>(_ fa: Kind<Self, A>) -> A {
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return fold(fa)
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}
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/// Transforms the elements of a structure to a type with a `Monoid` instance and folds them using the empty and combine methods of such `Monoid` instance.
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///
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/// - Parameters:
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/// - fa: Value to be transformed and folded.
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/// - f: Transforming function.
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/// - Returns: Summary value resulting from the transformation and folding process.
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static func foldMap<A, B: Monoid>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> B) -> B {
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return foldLeft(fa, B.empty(), { b, a in b.combine(f(a)) })
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}
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/// Traverses a structure of values, transforming them with a provided function and discarding the result of its effect.
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///
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/// - Parameters:
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/// - fa: Structure of values.
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/// - f: Transforming function.
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/// - Returns: Unit in the context of the effect of the result of the transforming function.
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static func traverse_<G: Applicative, A, B>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> Kind<G, B>) -> Kind<G, Unit> {
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return foldRight(fa, Eval.always({ G.pure(unit) }), { a, acc in
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G.map2Eval(f(a), acc, { _, _ in unit })
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}).value()
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}
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/// Traverses a structure of effects, performing them and discarding their result.
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///
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/// - Parameter fga: Structure of effects.
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/// - Returns: Unit in the context of the effects contained in the structure.
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static func sequence_<G: Applicative, A>(_ fga: Kind<Self, Kind<G, A>>) -> Kind<G, Unit> {
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return traverse_(fga, id)
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}
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/// Looks for an element that matches a given predicate.
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///
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/// - Parameters:
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/// - fa: Structure of values where the element matching the predicate needs to be found.
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/// - f: Predicate.
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/// - Returns: A value if there is any that matches the predicate, or `Option.none`.
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static func find<A>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> Bool) -> Option<A> {
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return foldRight(fa, Eval.now(Option.none()), { a, lb in
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f(a) ? Eval.now(Option.some(a)) : lb
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}).value()
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}
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/// Checks if any element in a structure matches a given predicate.
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///
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/// - Parameters:
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/// - fa: Structure of values where the element matching the predicate needs to be found.
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/// - predicate: Predicate.
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/// - Returns: A boolean value indicating if any elements in the structure match the predicate.
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static func exists<A>(_ fa: Kind<Self, A>, _ predicate: @escaping (A) -> Bool) -> Bool {
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return foldRight(fa, Eval.false, { a, lb in
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predicate(a) ? Eval.true : lb
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}).value()
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}
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/// Checks if all elements in a structure match a given predicate.
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///
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/// - Parameters:
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/// - fa: Structure of values where all elements should match the predicate.
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/// - predicate: Predicate.
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/// - Returns: A boolean value indicating if all elements in the structure match the predicate.
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static func forall<A>(_ fa: Kind<Self, A>, _ predicate: @escaping (A) -> Bool) -> Bool {
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return foldRight(fa, Eval.true, { a, lb in
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predicate(a) ? lb : Eval.false
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}).value()
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}
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/// Checks if a structure of values is empty.
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///
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/// - Parameter fa: Structure of values.
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/// - Returns: `false` if the structure contains any value, `true` otherwise.
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static func isEmpty<A>(_ fa: Kind<Self, A>) -> Bool {
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return foldRight(fa, Eval.true, { _, _ in Eval.false }).value()
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}
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/// Checks if a structure of values is not empty.
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///
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/// - Parameter fa: Structure of values.
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/// - Returns: `true` if the structure contains any value, `false` otherwise.
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static func nonEmpty<A>(_ fa: Kind<Self, A>) -> Bool {
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return !isEmpty(fa)
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}
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/// Performs a monadic left fold from the source context to the target monad.
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///
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/// - Parameters:
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/// - fa: Structure of values.
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/// - b: Initial value for the fold.
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/// - f: Folding function.
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/// - Returns: Summary value resulting from the folding process in the context of the target monad.
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static func foldM<G: Monad, A, B>(_ fa: Kind<Self, A>, _ b: B, _ f: @escaping (B, A) -> Kind<G, B>) -> Kind<G, B> {
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return foldLeft(fa, G.pure(b), { gb, a in G.flatMap(gb, { b in f(b, a) }) })
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}
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/// Performs a monadic left fold by mapping the values in a structure to ones in the target monad context and using the `Monoid` instance to combine them.
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///
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/// - Parameters:
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/// - fa: Structure of values.
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/// - f: Trasnforming function.
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/// - Returns: Summary value resulting from the transformation and folding process in the context of the target monad.
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static func foldMapM<G: Monad, A, B: Monoid>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> Kind<G, B>) -> Kind<G, B> {
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return foldM(fa, B.empty(), { b, a in G.map(f(a), { bb in b.combine(bb) }) })
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}
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/// Obtains a specific element of a structure of elements given its indexed position.
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///
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/// - Parameters:
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/// - fa: Structure of values.
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/// - index: Indexed position of the element to retrieve.
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/// - Returns: A value if there is any at the given position, or `Option.none` otherwise.
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static func get<A>(_ fa: Kind<Self, A>, _ index: Int64) -> Option<A> {
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return Either.fix(foldM(fa, Int64(0), { i, a in
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(i == index) ?
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Either<A, Int64>.left(a) :
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Either<A, Int64>.right(i + 1)
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})).fold(Option<A>.some,
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constant(Option<A>.none()))
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}
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/// Counts how many elements a structure contains.
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///
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/// - Parameter fa: Structure of values.
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/// - Returns: An integer value with the count of how many elements are contained in the structure.
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static func count<A>(_ fa: Kind<Self, A>) -> Int64 {
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return foldMap(fa, constant(1))
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}
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static func foldK<A, G: MonoidK>(_ fga: Kind<Self, Kind<G, A>>) -> Kind<G, A> {
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return reduceK(fga)
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}
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static func reduceK<A, G: MonoidK>(_ fga: Kind<Self, Kind<G, A>>) -> Kind<G, A> {
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return foldLeft(fga, Kind<G, A>.emptyK(), { b, a in b.combineK(a) })
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}
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}
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// MARK: Syntax for Foldable
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public extension Kind where F: Foldable {
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/// Eagerly folds this value to a summary value from left to right.
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///
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/// - Parameters:
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/// - b: Initial value for the folding process.
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/// - f: Folding function.
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/// - Returns: Summary value resulting from the folding process.
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func foldLeft<B>(_ b: B, _ f: @escaping (B, A) -> B) -> B {
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return F.foldLeft(self, b, f)
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}
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/// Lazily folds this value to a summary value from right to left.
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///
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/// - Parameters:
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/// - b: Initial value for the folding process.
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/// - f: Folding function.
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/// - Returns: Summary value resulting from the folding process.
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func foldRight<B>(_ b: Eval<B>, _ f: @escaping (A, Eval<B>) -> Eval<B>) -> Eval<B> {
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return F.foldRight(self, b, f)
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}
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/// Reduces the elements of this structure down to a single value by applying the provided transformation and aggregation funtions in a left-associative manner.
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///
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/// - Parameters:
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/// - f: Transforming function.
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/// - g: Folding function.
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/// - Returns: Optional summary value resulting from the folding process. It will be an `Option.none` if the structure is empty, or a value if not.
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func reduceLeftToOption<B>(_ f: @escaping (A) -> B, _ g: @escaping (B, A) -> B) -> Option<B> {
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return F.reduceLeftToOption(self, f, g)
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}
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/// Reduces the elements of this structure down to a single value by applying the provided transformation and aggregation functions in a right-associative manner.
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///
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/// - Parameters:
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/// - f: Transforming function.
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/// - g: Folding function.
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/// - Returns: Optional summary value resulting from the folding process. It will be an `Option.none` if the structure is empty, or a value if not.
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func reduceRightToOption<B>(_ f: @escaping (A) -> B, _ g: @escaping (A, Eval<B>) -> Eval<B>) -> Eval<Option<B>> {
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return F.reduceRightToOption(self, f, g)
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}
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/// Reduces the elements of this structure down to a single value by applying the provided aggregation function in a left-associative manner.
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///
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/// - Parameters:
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/// - f: Folding function.
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/// - Returns: Optional summary value resulting from the folding process.
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func reduceLeftOption(_ f: @escaping (A, A) -> A) -> Option<A> {
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return F.reduceLeftOption(self, f)
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280
|
|
}
|
|
281
|
|
|
|
282
|
|
/// Reduces the elements of this structure down to a single value by applying the provided aggregation function in a right-associative manner.
|
|
283
|
|
///
|
|
284
|
|
/// - Parameters:
|
|
285
|
|
/// - f: Folding function.
|
|
286
|
|
/// - Returns: Optional summary value resulting from the folding process.
|
|
287
|
0
|
func reduceRightOption(_ f: @escaping (A, Eval<A>) -> Eval<A>) -> Eval<Option<A>> {
|
|
288
|
0
|
return F.reduceRightOption(self, f)
|
|
289
|
|
}
|
|
290
|
|
|
|
291
|
|
/// Transforms the elements of this structure to a type with a `Monoid` instance and folds them using the empty and combine methods of such `Monoid` instance.
|
|
292
|
|
///
|
|
293
|
|
/// - Parameters:
|
|
294
|
|
/// - fa: Value to be transformed and folded.
|
|
295
|
|
/// - f: Transforming function.
|
|
296
|
|
/// - Returns: Summary value resulting from the transformation and folding process.
|
|
297
|
1
|
func foldMap<B: Monoid>(_ f: @escaping (A) -> B) -> B {
|
|
298
|
1
|
return F.foldMap(self, f)
|
|
299
|
|
}
|
|
300
|
|
|
|
301
|
|
/// Traverses this structure of values, transforming them with a provided function and discarding the result of its effect.
|
|
302
|
|
///
|
|
303
|
|
/// - Parameters:
|
|
304
|
|
/// - f: Transforming function.
|
|
305
|
|
/// - Returns: Unit in the context of the effect of the result of the transforming function.
|
|
306
|
0
|
func traverse_<G: Applicative, B>(_ f: @escaping (A) -> Kind<G, B>) -> Kind<G, Unit> {
|
|
307
|
0
|
return F.traverse_(self, f)
|
|
308
|
|
}
|
|
309
|
|
|
|
310
|
|
/// Traverses this structure of effects, performing them and discarding their result.
|
|
311
|
|
///
|
|
312
|
|
/// - Returns: Unit in the context of the effects contained in the structure.
|
|
313
|
0
|
func sequence_<G: Applicative, AA>() -> Kind<G, Unit> where A == Kind<G, AA> {
|
|
314
|
0
|
return F.sequence_(self)
|
|
315
|
|
}
|
|
316
|
|
|
|
317
|
|
/// Looks for an element that matches a given predicate.
|
|
318
|
|
///
|
|
319
|
|
/// - Parameters:
|
|
320
|
|
/// - f: Predicate.
|
|
321
|
|
/// - Returns: A value if there is any that matches the predicate, or `Option.none`.
|
|
322
|
0
|
func find(_ f: @escaping (A) -> Bool) -> Option<A> {
|
|
323
|
0
|
return F.find(self, f)
|
|
324
|
|
}
|
|
325
|
|
|
|
326
|
|
/// Checks if any element in this structure matches a given predicate.
|
|
327
|
|
///
|
|
328
|
|
/// - Parameters:
|
|
329
|
|
/// - predicate: Predicate.
|
|
330
|
|
/// - Returns: A boolean value indicating if any elements in the structure match the predicate.
|
|
331
|
1
|
func exists(_ predicate: @escaping (A) -> Bool) -> Bool {
|
|
332
|
1
|
return F.exists(self, predicate)
|
|
333
|
|
}
|
|
334
|
|
|
|
335
|
|
/// Checks if all elements in this structure match a given predicate.
|
|
336
|
|
///
|
|
337
|
|
/// - Parameters:
|
|
338
|
|
/// - predicate: Predicate.
|
|
339
|
|
/// - Returns: A boolean value indicating if all elements in the structure match the predicate.
|
|
340
|
1
|
func forall(_ predicate: @escaping (A) -> Bool) -> Bool {
|
|
341
|
1
|
return F.forall(self, predicate)
|
|
342
|
|
}
|
|
343
|
|
|
|
344
|
|
/// Checks if this structure of values is empty.
|
|
345
|
|
///
|
|
346
|
|
/// - Returns: `false` if the structure contains any value, `true` otherwise.
|
|
347
|
1
|
var isEmpty: Bool {
|
|
348
|
1
|
return F.isEmpty(self)
|
|
349
|
|
}
|
|
350
|
|
|
|
351
|
|
/// Checks if this structure of values is not empty.
|
|
352
|
|
///
|
|
353
|
|
/// - Returns: `true` if the structure contains any value, `false` otherwise.
|
|
354
|
0
|
var nonEmpty: Bool {
|
|
355
|
0
|
return F.nonEmpty(self)
|
|
356
|
|
}
|
|
357
|
|
|
|
358
|
|
/// Performs a monadic left fold from the source context to the target monad.
|
|
359
|
|
///
|
|
360
|
|
/// - Parameters:
|
|
361
|
|
/// - b: Initial value for the fold.
|
|
362
|
|
/// - f: Folding function.
|
|
363
|
|
/// - Returns: Summary value resulting from the folding process in the context of the target monad.
|
|
364
|
0
|
func foldM<G: Monad, B>(_ b: B, _ f: @escaping (B, A) -> Kind<G, B>) -> Kind<G, B> {
|
|
365
|
0
|
return F.foldM(self, b, f)
|
|
366
|
|
}
|
|
367
|
|
|
|
368
|
|
/// Performs a monadic left fold by mapping the values in this structure to ones in the target monad context and using the `Monoid` instance to combine them.
|
|
369
|
|
///
|
|
370
|
|
/// - Parameters:
|
|
371
|
|
/// - f: Trasnforming function.
|
|
372
|
|
/// - Returns: Summary value resulting from the transformation and folding process in the context of the target monad.
|
|
373
|
0
|
func foldMapM<G: Monad, B: Monoid>(_ f: @escaping (A) -> Kind<G, B>) -> Kind<G, B> {
|
|
374
|
0
|
return F.foldMapM(self, f)
|
|
375
|
|
}
|
|
376
|
|
|
|
377
|
|
/// Obtains a specific element of a structure of elements given its indexed position.
|
|
378
|
|
///
|
|
379
|
|
/// - Parameters:
|
|
380
|
|
/// - index: Indexed position of the element to retrieve.
|
|
381
|
|
/// - Returns: A value if there is any at the given position, or `Option.none` otherwise.
|
|
382
|
0
|
func get(_ index: Int64) -> Option<A> {
|
|
383
|
0
|
return F.get(self, index)
|
|
384
|
|
}
|
|
385
|
|
|
|
386
|
|
/// Counts how many elements this structure contains.
|
|
387
|
|
///
|
|
388
|
|
/// - Returns: An integer value with the count of how many elements are contained in the structure.
|
|
389
|
1
|
var count: Int64 {
|
|
390
|
1
|
return F.count(self)
|
|
391
|
|
}
|
|
392
|
|
|
|
393
|
1
|
func foldK<G: MonoidK, B>() -> Kind<G, B> where A == Kind<G, B> {
|
|
394
|
1
|
return F.foldK(self)
|
|
395
|
|
}
|
|
396
|
|
|
|
397
|
0
|
func reduceK<G: MonoidK, B>() -> Kind<G, B> where A == Kind<G, B> {
|
|
398
|
0
|
return F.reduceK(self)
|
|
399
|
|
}
|
|
400
|
|
}
|
|
401
|
|
|
|
402
|
|
public extension Kind where F: Foldable, A: Monoid {
|
|
403
|
|
/// Folds this structure of values provided that its type has an instance of `Monoid`.
|
|
404
|
|
///
|
|
405
|
|
/// It uses the monoid empty value as initial value and the combination method for the fold.
|
|
406
|
|
///
|
|
407
|
|
/// - Returns: Summary value resulting from the folding process.
|
|
408
|
0
|
func fold() -> A {
|
|
409
|
0
|
return F.fold(self)
|
|
410
|
|
}
|
|
411
|
|
|
|
412
|
|
/// Folds this structure of values provided that its type has an instance of `Monoid`.
|
|
413
|
|
///
|
|
414
|
|
/// It uses the monoid empty value as initial value and the combination method for the fold.
|
|
415
|
|
///
|
|
416
|
|
/// - Returns: Summary value resulting from the folding process.
|
|
417
|
0
|
func combineAll() -> A {
|
|
418
|
0
|
return F.combineAll(self)
|
|
419
|
|
}
|
|
420
|
|
}
|
truizlop