@thi.ng/transducers/juxtr.js

Collection of ~170 lightweight, composable transducers, reducers, generators, iterators for functional data transformations

import { isReduced, reduced, unreduced } from "./reduced.js";
function juxtR(...rs) {
  let [a, b, c] = rs;
  const n = rs.length;
  switch (n) {
    case 1: {
      const r = a[2];
      return [
        () => [a[0]()],
        (acc) => [a[1](acc[0])],
        (acc, x) => {
          const aa1 = r(acc[0], x);
          if (isReduced(aa1)) {
            return reduced([unreduced(aa1)]);
          }
          return [aa1];
        }
      ];
    }
    case 2: {
      const ra = a[2];
      const rb = b[2];
      return [
        () => [a[0](), b[0]()],
        (acc) => [a[1](acc[0]), b[1](acc[1])],
        (acc, x) => {
          const aa1 = ra(acc[0], x);
          const aa2 = rb(acc[1], x);
          if (isReduced(aa1) || isReduced(aa2)) {
            return reduced([unreduced(aa1), unreduced(aa2)]);
          }
          return [aa1, aa2];
        }
      ];
    }
    case 3: {
      const ra = a[2];
      const rb = b[2];
      const rc = c[2];
      return [
        () => [a[0](), b[0](), c[0]()],
        (acc) => [a[1](acc[0]), b[1](acc[1]), c[1](acc[2])],
        (acc, x) => {
          const aa1 = ra(acc[0], x);
          const aa2 = rb(acc[1], x);
          const aa3 = rc(acc[2], x);
          if (isReduced(aa1) || isReduced(aa2) || isReduced(aa3)) {
            return reduced([
              unreduced(aa1),
              unreduced(aa2),
              unreduced(aa3)
            ]);
          }
          return [aa1, aa2, aa3];
        }
      ];
    }
    default:
      return [
        () => rs.map((r) => r[0]()),
        (acc) => rs.map((r, i) => r[1](acc[i])),
        (acc, x) => {
          let done = false;
          const res = [];
          for (let i = 0; i < n; i++) {
            let a2 = rs[i][2](acc[i], x);
            if (isReduced(a2)) {
              done = true;
              a2 = unreduced(a2);
            }
            res[i] = a2;
          }
          return done ? reduced(res) : res;
        }
      ];
  }
}
export {
  juxtR
};