@effect-ts/system/_src/Managed/methods/loop.ts

Effect-TS is a zero dependency set of libraries to write highly productive, purely functional TypeScript at scale.

// ets_tracing: off

import { pipe } from "../../Function/index.js"
import { chain_, map } from "../core.js"
import type { Managed } from "../managed.js"
import { succeed } from "../succeed.js"
import { unit } from "./api.js"
import { suspend } from "./suspend.js"

/**
 * Loops with the specified effectual function, collecting the results into a
 * list. The moral equivalent of:
 *
 * ```
 * let s  = initial
 * let as = [] as readonly A[]
 *
 * while (cont(s)) {
 *   as = [body(s), ...as]
 *   s  = inc(s)
 * }
 *
 * A.reverse(as)
 * ```
 */
export function loop<Z>(initial: Z, cont: (z: Z) => boolean, inc: (z: Z) => Z) {
  return <R, E, A>(
    body: (z: Z) => Managed<R, E, A>,
    __trace?: string
  ): Managed<R, E, readonly A[]> =>
    suspend(() => {
      if (cont(initial)) {
        return chain_(body(initial), (a) =>
          pipe(
            loop(inc(initial), cont, inc)(body),
            map((as) => [a, ...as])
          )
        )
      }
      return succeed([])
    }, __trace)
}

/**
 * Loops with the specified effectual function purely for its effects. The
 * moral equivalent of:
 *
 * ```
 * var s = initial
 *
 * while (cont(s)) {
 *   body(s)
 *   s = inc(s)
 * }
 * ```
 */
export function loopUnit<Z>(initial: Z, cont: (z: Z) => boolean, inc: (z: Z) => Z) {
  return <R, E, X>(
    body: (z: Z) => Managed<R, E, X>,
    __trace?: string
  ): Managed<R, E, void> =>
    suspend(() => {
      if (cont(initial)) {
        return chain_(body(initial), () => loopUnit(inc(initial), cont, inc)(body))
      }
      return unit
    }, __trace)
}