inamiy

-- Solving Fix / Mu / Nu exercise in
-- https://stackoverflow.com/questions/45580858/what-is-the-difference-between-fix-mu-and-nu-in-ed-kmetts-recursion-scheme-pac

{-# LANGUAGE RankNTypes, GADTs #-}

----------------------------------------
-- Fix / Mu / Nu

newtype Fix f = Fix { unFix :: f (Fix f) }

inamiy

// https://stackoverflow.com/questions/53011500/how-to-replace-properties-using-mapped-types-in-typescript
// https://twitter.com/inamiy/status/1278511811025711104

type ReplaceProps<T, From, To> = {
    [K in keyof T]: K extends keyof From
        ? T[K] extends From[K]
            ? K extends keyof To
                ? To[K]
                : T[K]
            : T[K]

inamiy

// https://twitter.com/inamiy/status/1257538502226358272

struct Hashable1: Hashable {
    struct Hashable1a: Hashable {}
}
struct Hashable2: Hashable {}

Hashable1().hashValue
Hashable1.Hashable1a().hashValue
Hashable2().hashValue

inamiy

Just(())
    .delay(for: 1, scheduler: DispatchQueue.main)
    .sink {
        print("Q1. Can you hear me?") // Yes, even without retaining cancellable. Do you know why? :)
    }

Just(())
    .delay(for: 1, scheduler: DispatchQueue.main)
    .flatMap { Just(()) }
    .sink {

inamiy

take 9 $ [0..] >>= flip replicateM [0, 1]
-- [[],[0],[1],[0,0],[0,1],[1,0],[1,1],[0,0,0],[0,0,1]]

inamiy

-- Data types a la carte
-- http://www.cs.ru.nl/~W.Swierstra/Publications/DataTypesALaCarte.pdf

-- [Wadler's Blog: Data Types a la Carte](http://wadler.blogspot.com/2008/02/data-types-la-carte.html)

{-# LANGUAGE TypeOperators, MultiParamTypeClasses, FlexibleInstances, FlexibleContexts, ScopedTypeVariables #-}

----------------------------------------
-- Expression Problem
----------------------------------------

inamiy

fmap . fmap . fmap
  :: (Functor f1, Functor f2, Functor f3) =>
     (a -> b) -> f1 (f2 (f3 a)) -> f1 (f2 (f3 b))

fmap . fmap . fmap
== fmap . (fmap . fmap)
== fmap . (fmap fmap fmap)
== fmap fmap (fmap fmap fmap)
== (fmap fmap . fmap fmap) fmap
== fmap (fmap fmap) (fmap fmap) fmap

inamiy

// Private Conformance (Generic Manifesto)
// https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#private-conformances
//
// > Right now, a protocol conformance can be no less visible than the minimum of the conforming type's access and the protocol's access.
// > Therefore, a public type conforming to a public protocol must provide the conformance publicly.
// > The main problem with private conformances is the interaction with dynamic casting

public protocol PublicProtocol {
    var foo: String { get }
}

inamiy

// Xcode 11.1 indent style

[1, 2, 3]
    .filter { x in
        x.isMultiple(of: 2)
}
.map { $0 }
.map { $0 }

[1, 2, 3]

inamiy

public protocol Transformer {
    associatedtype To
    associatedtype From
    static func convert(to: To) throws -> From
    static func convert(from: From) throws -> To
}

@propertyWrapper
public struct CustomCodable<T: Transformer> {
    public var wrappedValue: T.To