59 lines
1.9 KiB
TypeScript
59 lines
1.9 KiB
TypeScript
//---------------------------------------------------------------------------
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// @syndicate-lang/core, an implementation of Syndicate dataspaces for JS.
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// Copyright (C) 2016-2021 Tony Garnock-Jones <tonyg@leastfixedpoint.com>
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>.
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//---------------------------------------------------------------------------
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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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