Iterators

iterators.ts

import assert from "assert";
import { Option, isSome, none, some } from '@keiii/k-stream';

const range = (
  [a, b]: [number, number],
  inclusive = false
): Iterable<number> => {
  assert(b >= a, "Invalid range");
  const isDone = inclusive ? (x: number) => x > b : (x: number) => x >= b;
  return {
    [Symbol.iterator]: (): Iterator<number> => {
      let current = a;
      return {
        next: (): IteratorResult<number> => {
          return isDone(current)
            ? { done: true, value: current }
            : { done: false, value: current++ };
        },
      };
    },
  };
};

const filterMap = <A, B>(
  ia: Iterable<A>,
  f: (a: A) => Option<B>,
): Iterable<B> => {
  return {
    [Symbol.iterator]: () => {
      const i = ia[Symbol.iterator]();
      let current;
      const go = (): IteratorResult<B> => {
        current = i.next();
        if (current.done) return { done: true, value: current.value };
        const x = f(current.value);
        return isSome(x) ? { done: false, value: x.value } : go();
      };
      return { next: go };
    },
  };
};

const map = <A, B>(ia: Iterable<A>, f: (a: A) => B): Iterable<B> => {
  return {
    [Symbol.iterator]: () => {
      const i = ia[Symbol.iterator]();
      let current;
      return {
        next: () => {
          current = i.next();
          return current.done
            ? { done: true, value: current.value }
            : {
                done: false,
                value: f(current.value),
              };
        },
      };
    },
  };
};