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Experiments with partial function application in Swift
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| func partial<A, B, T>(f: (A, B) -> T, a: A) -> (B) -> T { | |
| return { f(a, $0) } | |
| } | |
| func bind2nd<A, B, T>(f: (A, B) -> T, b: B) -> (A) -> T { | |
| return { f($0, b) } | |
| } | |
| func partial<A, B, C, T>(f: (A, B, C) -> T, a: A) -> (B, C) -> T { | |
| return { f(a, $0, $1) } | |
| } | |
| func partial<A, B, C, T>(f: (A, B, C) -> T, a: A, b: B) -> (C) -> T { | |
| return { f(a, b, $0) } | |
| } | |
| func partial<A, B, C, D, T>(f: (A, B, C, D) -> T, a: A, b: B, c: C) -> (D) -> T { | |
| return { f(a, b, c, $0) } | |
| } | |
| func partial<A, B, C, D, T>(f: (A, B, C, D) -> T, a: A, b: B) -> (C, D) -> T { | |
| return { f(a, b, $0, $1) } | |
| } | |
| func partial<A, B, C, D, T>(f: (A, B, C, D) -> T, a: A) -> (B, C, D) -> T { | |
| return { f(a, $0, $1, $2) } | |
| } | |
| // pipe-forward operator used in examples | |
| operator infix |> { associativity left } | |
| func |> <A, B>(a: A, f: A -> B) -> B { | |
| return f(a) | |
| } | |
| // Numeric examples | |
| func add(a: Int, b: Int) -> Int { return a + b } | |
| func subtract(a: Int, b: Int) -> Int { return a - b } | |
| let addOneTo = partial(add, 1) | |
| let subtractFromOne = partial(subtract, 1) | |
| let subtractOneFrom = bind2nd(subtract, 1) | |
| addOneTo(10) // 11 | |
| subtractOneFrom(10) // 9 | |
| subtractFromOne(10) // -9 | |
| 100 |> addOneTo |> addOneTo // 102 | |
| // String examples | |
| func join2(a: String, b: String) -> String { | |
| return a + b | |
| } | |
| func join3(a: String, b: String, c: String) -> String { | |
| return a + b + c | |
| } | |
| join2("Hello, ", "world!") // "Hello, world!" | |
| join3("1", "2", "3") // "123" | |
| let prependHello = partial(join2, "Hello, ") | |
| prependHello("Dolly") // "Hello, Dolly" | |
| let appendWorld = bind2nd(join2, "World!") | |
| appendWorld("Goodbye, ") // "Goodbye, World!" | |
| let prependFirstSecond = partial(join3, "First ", "Second ") | |
| prependFirstSecond("Third") // "First Second Third" | |
| let prependFirst = partial(join3, "First ") | |
| prependFirst("Second ", "Third") // "First Second Third" | |
| func bracket(prefix: String, suffix: String, s: String) -> String { | |
| return prefix + s + suffix | |
| } | |
| "Hello" // "<div><p>Hello</p></div>" | |
| |> partial(bracket, "<p>", "</p>") | |
| |> partial(bracket, "<div>", "</div>") |
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