List comprehensions
Basic idea in theoretical programming: a notation for Set builders from math.
Basic idea in practical programming: syntactic sugar for "map + filter" functional methods:
Example of map and filter, ES6
let x = N.filter(x => x > 10).map(x => x * x);Can be written as:
let x = [for (let x of N) if (x > 10) x * x];P.S.: details:
Set builder notation
In Math: (sounds as: "Build me a set consisting of squares of numbers from the natural numbers set, but only if a number is greater than 10")
x = {x · x | x ∈ N ^ x > 10}
In programming languages:
Erlang
X = [X * X | X <- N, X > 10]Python
x = [x * x for x in N if x > 10]JavaScript 1.8 (before ES6)
var x = [x * x for each (x in N) if (x > 10)];Previous ECMAScript 6 proposal
let x = [x * x for x of N if x > 10];ECMAScript 6 (current): swapped parts to look it similar to simple for-loop
let x = [for (let x of N) if (x > 10) x * x];Reference