ApplicativeSwift

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ApplicativeSwift

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Provides the operators to realize the applicative style for Swift, which is used in Haskell.

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ApplicativeSwift
=========================

_ApplicativeSwift_ provides the operators to realize the __applicative style__ for Swift, which is used in Haskell.

```swift
let a: Int? = 2
let b: Int? = 3

let result: Int? = (+) <^> a <*> b // Optional(5)
```

Purpose
-------------------------

We use a lot of `Optional` values in Swift. Sometimes we want to apply operators or functions to 2 or more optional values. But it is too complicated.

```swift
let a: Int? = 2
let b: Int? = 3

// How to calculate a + b? (wants nil if a or b is nil)

// Too complicated
let result: Int? = {
    if let a0 = a {
        if let b0 = b {
            return a0 + b0
        }
    }
    return nil
}()
```

In Haskell, it can be done easily in the applicative style.

```haskell
-- Haskell
(+) <$> a <*> b
```

_ApplicativeSwift_ provides such operators for Swift. Because the letter `$` cannot be used for operators in Swift, _ApplicativeSwift_ provides `<^>` instead of `<$>`. Therefore `a + b` can be calculated in the following way.

```swift
// Swift
(+) <^> a <*> b
```

Usage
-------------------------

```swift
// Optional
let a: Int? = 2
let b: Int? = 3
let c: Int? = 5
let d: Int? = 7
let e: Int? = 11
let f: Int? = 13
let g: Int? = 17

(+) <^> a <*> b
sum3 <^> a <*> b <*> c
sum4 <^> a <*> b <*> c <*> d
sum5 <^> a <*> b <*> c <*> d <*> e
sum6 <^> a <*> b <*> c <*> d <*> e <*> f
sum7 <^> a <*> b <*> c <*> d <*> e <*> f <*> g

// Array
(*) <^> [1, 2] <*> [3, 4]

// Currying
curry(+)(2) <*> .Some(3)
[curry(+), curry(*)] <*> [1, 2] <*> [3, 4]
```

Installation
-------------------------

### Carthage

[_Carthage_](https://github.com/Carthage/Carthage) is available to install _ApplicativeSwift_. Add it to your _Cartfile_:

```
github "koher/ApplicativeSwift" ~> 2.0.0
```

### Manually

#### Embedded Framework

For iOS 8 or later,

1. Put [ApplicativeSwift.xcodeproj](ApplicativeSwift.xcodeproj) into your project in Xcode.
2. Click the project icon and select the "General" tab.
3. Add ApplicativeSwift.framework to "Embedded Binaries".
4. `import ApplicativeSwift` in your swift files.

#### Source

For iOS 7, put [Applicative.swift](ApplicativeSwift/Applicative.swift) into your project.

License
-------------------------

[The MIT License](LICENSE)

References
-------------------------

1. [Applicative functors - Learn You a Haskell for Great Good!](http://learnyouahaskell.com/functors-applicative-functors-and-monoids#applicative-functors)
2. [Advanced Operators - The Swift Programming Language](https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html)

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