62 lines
1.4 KiB
TypeScript
62 lines
1.4 KiB
TypeScript
/// SPDX-License-Identifier: GPL-3.0-or-later
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/// SPDX-FileCopyrightText: Copyright © 2016-2023 Tony Garnock-Jones <tonyg@leastfixedpoint.com>
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export type NonEmptyStack<T> = { item: T, rest: Stack<T> };
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export type Stack<T> = null | NonEmptyStack<T>;
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export function empty<T>(): Stack<T> {
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return null;
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}
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export function push<T>(item: T, rest: Stack<T>): NonEmptyStack<T> {
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return { item, rest };
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}
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export function isEmpty<T>(s: Stack<T>): s is null {
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return s === null;
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}
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export function nonEmpty<T>(s: Stack<T>): s is NonEmptyStack<T> {
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return s !== null;
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}
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export function rest<T>(s: Stack<T>): Stack<T> {
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if (nonEmpty(s)) {
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return s.rest;
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} else {
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throw new Error("pop from empty Stack");
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}
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}
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export function drop<T>(s: Stack<T>, n: number): Stack<T> {
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while (n--) s = rest(s);
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return s;
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}
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export function dropNonEmpty<T>(s: NonEmptyStack<T>, n: number): NonEmptyStack<T> {
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while (n--) {
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const next = s.rest;
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if (!nonEmpty(next)) throw new Error("dropNonEmpty popped too far");
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s = next;
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}
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return s;
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}
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export function depth<T>(s: Stack<T>): number {
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let count = 0;
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while (s !== null) {
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count++;
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s = s.rest;
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}
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return count;
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}
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export function toArray<T>(s: Stack<T>): T[] {
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const result = [];
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while (s !== null) {
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result.push(s.item);
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s = s.rest;
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}
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return result;
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}
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