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aal89/currying.swift

Last active Sep 26, 2019
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Examples whereby we curry an arithmetic operator over a collection of natural numbers and curry a greetings functions over a collection of strings, in Swift.
// ========================== Generic (limited) curry function:
func curry<A, B, C>(_ f: @escaping (A, B) -> C) -> (A) -> (B) -> C {
return { a in { b in f(a, b) }}
}
// ========================== Example 1:
let add = curry((+) as ((Int, Int) -> Int))
let add2 = add(2)
let numbers = 1...100
numbers.map(add2) // [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102]
// ========================== Example 2:
let stringConcat = { (s1: String, s2: String) in
return "\(s1) \(s2)"
}
let curriedStringConcat = curry(stringConcat)
let sayHi = curriedStringConcat("Hello")
[
"John",
"Jane"
].map(sayHi) // ["Hello John", "Hello Jane"]
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