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import Foundation
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/// A Contravariant Functor is the dual of a Covariant Functor, usually referred to as just `Functor`. Whereas an intuition behind Covariant Functors is that they can be seen as containing or producing values, Contravariant Functors can be seen as consuming values.
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public protocol Contravariant: Invariant {
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/// Creates a new value transforming the type using the provided function, preserving the structure of the original type.
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///
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/// - Parameters:
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/// - fa: Value to be transformed.
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/// - f: Transforming function.
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/// - Returns: The result of transforming the value type using the provided function, maintaining the structure of the original value.
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static func contramap<A, B>(_ fa: Kind<Self, A>, _ f: @escaping (B) -> A) -> Kind<Self, B>
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}
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public extension Contravariant {
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// Docs inherited from `Invariant`.
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static func imap<A, B>(_ fa: Kind<Self, A>, _ f: @escaping (A) -> B, _ g: @escaping (B) -> A) -> Kind<Self, B> {
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return contramap(fa, g)
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}
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/// Given a function, provides a new function lifted to the context type implementing this instance of `Contravariant`, but reversing the direction of the arrow.
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///
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/// - Parameter f: Function to be lifted.
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/// - Returns: Function in the context implementing this instance.
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static func contralift<A, B>(_ f: @escaping (A) -> B) -> (Kind<Self, B>) -> Kind<Self, A> {
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return { fa in contramap(fa, f) }
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}
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}
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// MARK: Syntax for Contravariant
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public extension Kind where F: Contravariant {
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/// Creates a new value transforming the type using the provided function, preserving the structure of the original type.
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///
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/// - Parameters:
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/// - f: Transforming function.
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/// - Returns: The result of transforming the value type using the provided function, maintaining the structure of the original value.
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func contramap<B>(_ f : @escaping (B) -> A) -> Kind<F, B> {
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return F.contramap(self, f)
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}
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/// Given a function, provides a new function lifted to the context type implementing this instance of `Contravariant`, but reversing the direction of the arrow.
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///
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/// - Parameter f: Function to be lifted.
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/// - Returns: Function in the context implementing this instance.
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static func contralift<B>(_ f : @escaping (A) -> B) -> (Kind<F, B>) -> Kind<F, A> {
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return F.contralift(f)
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}
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}
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truizlop