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import Foundation
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/// An Invariant Functor provides a type the ability to transform its value type into another type. An instance of `Functor` or `Contravariant` are Invariant Functors as well.
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public protocol Invariant {
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/// Transforms the value type using the functions provided.
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///
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/// The implementation of this function must obey the following laws:
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///
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/// imap(fa, id, id) == fa
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/// imap(imap(fa, f1, g1), f2, g2) == imap(fa, compose(f2, f1), compose(g2, g1))
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///
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/// - Parameters:
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/// - fa: Value whose value type will be transformed.
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/// - f: Transforming function.
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/// - g: Transforming function.
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/// - Returns: A new value in the same context as the original value, with the value type transformed.
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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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}
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// MARK: Syntax for Invariant
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public extension Kind where F: Invariant {
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/// Transforms the value type using the functions provided.
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///
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/// This is a conveninece method to call `Invariant.imap` as an instance method.
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///
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/// - Parameters:
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/// - f: Transforming function.
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/// - g: Transforming function.
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/// - Returns: A new value in the same context as the original value, with the value type transformed.
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func imap<B>(_ f : @escaping (A) -> B, _ g : @escaping (B) -> A) -> Kind<F, B> {
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return F.imap(self, f, g)
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}
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}
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truizlop