dduan/Comprehension

Installation

Swift Package Manager

.package(url: "git@github.com:dduan/Comprehension.git", .branch("master")),

(and "Comprehension" to the target's dependencies.)

CocoaPods

use_frameworks!

pod "Comprehension"

Carthage

github "dduan/Comprehension"

Direct Embed

Include Sources/Comprehension/Comprehension.swift in your project.

What's List Comprehension?

List comprehension is a powerful syntax for processing lists in languages such as Haskell, Python, etc. It's particularly handy when you need to deal with combinations of each elements in multiple lists (their [Cartesian product][2]).

The origin of list comprehension is often attribute to set comprehension in mathematics, whereas

{2·x|x ∈ ℕ, x ≤ 10}

… means "take all integers (element of set ℕ) that are less that 10, multiply each by 2 and form a new set with the results."

Here's an example of how list comprehension works in Haskell:

ghci> [x+y | x <- [1,2,3], y <- [10,100,1000]]
[11,101,1001,12,102,1002,13,103,1003]

Here, integers from one list is sequentially paired with that from the other list, resulting in 3 * 3 = 9 pairs. The sum of each pair forms the resulting list of integers.

Comprehension on a single list is equivalent of list.filter(f).map(g). When input is 2 lists:

// Comprehension syntax
let result = Array(list0, list1, where: f) { g($0, $1) }

… is equivalent of …

var result = [TypeOfElementInList0, TypeOfElementInList1]()
for e0 in list0 {
    for e1 in list1 {
        if f(e0, e1) {
            result.append(g(e0, e1))
        }
    }
}
// The fact that `result` is a var is not equivalent, but 🤷‍♀️.

… or in functional style …

let result = list0
    .map { e0 in
        list1.map { e1 in
            (e0, e1)
        }
    }
    .joined()
    .filter(f)
    .map(g)

Note how the list comprehension version is much more concise above. And imagine expanding the example to 3, 4, 5 lists!

License

MIT, see [LICENSE][3].

[1]: https://en.wikipedia.org/wiki/List_comprehension [2]: https://en.wikipedia.org/wiki/Cartesian_product [3]: https://github.com/dduan/Comprehension/blob/master/LICENSE.md

Package Metadata

Repository: dduan/Comprehension

Stars: 17

Forks: 1

Open issues: 0

Default branch: master

Primary language: swift

License: MIT

Topics: swift

README: README.md