even-odd-generator.js

even-odd-generator.js

const fill = function* (start = 0, end = 100, filter = (_) => true, mapper = (x) => x) {
    while (start < end) {
        if (filter(start))
            yield start;
        mapper(start++);
    }
};
const isEven = (num) => num % 2 === 0;
const isOdd = (num) => num % 2 !== 0;
const evens = [...fill(0, 100, isEven)];
const odds = [...fill(0, 100, isOdd)];
const evensSquares = [...fill(0, 100, isEven, (x) => x * x)];

console.log(evens); //[0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,92,94,96,98]
console.log(odds); //[1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,95,97,99]
console.log(evensSquares); //[0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,92,94,96,98]

const fillNaturalNumbers = (start, end) => fill(start, end + 1);
const naturals = [...fillNaturalNumbers(1, 100)];
console.log(naturals);//[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100]

fill.ts

/**
* Original author @christiantakle
*/

const identity = <A>(a: A) => a;
const constTrue = <A>(a: A) => true;

interface FillInput<A> {
  range: [start: number, end: number];
  filter: (a: number) => boolean;
  mapper: (a: number) => A;
}

function* fill<A>({
  range: [start, end],
  filter = constTrue,
  mapper,
}: FillInput<A>): Generator<A, void, undefined> {
  while (start < end) {
    if (filter(start)) yield mapper(start);
    start++;
  }
}

const isEven = (num: number) => num % 2 === 0;
const isOdd = (num: number) => num % 2 !== 0;
const evens = [
  ...fill({
    range: [1, 101],
    filter: isEven,
    mapper: identity,
  }),
];

console.log(evens);

console.log([
  ...fill({
    range: [1, 101],
    filter: isEven,
    mapper: (x) => x * x,
  }),
]);

I tried something similar to write, However, the default to mapper still issue.

Type 'number' is not assignable to type 'A'.

If that could be solve.

@deepakshrma I've updated my first comment with information from our dialog. I removed the generics from the example where mapper is optional you cannot typecheck it unless you use any or unknown neither which is ideal.

I've also added an example with generics but you have to supply a mapper function to use it to make the type checker happy