Created
May 22, 2025 08:59
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Monadic handles for return values in do-notation for Cont
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| import { Cont } from "prelude"; | |
| let div = document.createElement("div"); | |
| div.style.setProperty("position", "absolute"); | |
| div.style.setProperty("left", "20px"); | |
| div.style.setProperty("top", "20px"); | |
| div.style.setProperty("width", "300px"); | |
| div.style.setProperty("z-index", "100"); | |
| div.style.setProperty("background-color", "rgba(0,0,0,0.7)"); | |
| setTimeout(() => { | |
| document.body.appendChild(div); | |
| main().run(); | |
| }, 3000); | |
| export function onUnload() { | |
| document.body.removeChild(div); | |
| } | |
| function main(): Cont<void> { | |
| return do_(() => { | |
| fork(proc("A", 4)); | |
| fork(proc("B", 2)); | |
| dequeue(); | |
| print("done main."); | |
| let name = ask("Whats your name?"); | |
| exec(name.then( | |
| (name) => do_(() => | |
| print(`Hello: ${name}`)) | |
| )); | |
| }); | |
| } | |
| function proc(id: string, n: number): Cont<void> { | |
| return do_(() => { | |
| for (let i = 1; i <= n; ++i) { | |
| sleep(1000); | |
| print(`${id}: ${i}`); | |
| pause(); | |
| } | |
| }); | |
| } | |
| let doContext: Cont<void> | undefined = undefined; | |
| function do_(fn: () => void): Cont<void> { | |
| let outer = doContext; | |
| try { | |
| doContext = undefined; | |
| fn(); | |
| return doContext ?? Cont.of<void>((k) => k()); | |
| } finally { | |
| doContext = outer; | |
| } | |
| } | |
| function exec(instr: Cont<void>) { | |
| if (doContext == undefined) { | |
| doContext = instr; | |
| } else { | |
| doContext = doContext.then((_) => instr); | |
| } | |
| } | |
| function ask(msg: string): Cont<string> { | |
| let result: string | undefined = undefined; | |
| let kResult: ((a: string) => void) | undefined = undefined; | |
| exec(Cont.of((k) => { | |
| result = window.prompt(msg); | |
| if (kResult != undefined) { | |
| kResult(result); | |
| } | |
| k(); | |
| })); | |
| return Cont.of((k) => { | |
| if (result != undefined) { | |
| k(result); | |
| } else { | |
| kResult = k; | |
| } | |
| }); | |
| } | |
| function print(msg: string) { | |
| exec(Cont.of((k) => { | |
| div.append(msg); | |
| div.appendChild(document.createElement("br")); | |
| k(); | |
| })); | |
| } | |
| function sleep(ms: number) { | |
| exec(Cont.of((k) => { | |
| setTimeout(k, ms); | |
| })); | |
| } | |
| const processQueue: Cont<void>[] = []; | |
| function pause() { | |
| exec(Cont.callCC<void, void>((k) => { | |
| processQueue.push(k()); | |
| return do_(dequeue); | |
| })); | |
| } | |
| function dequeue() { | |
| exec(Cont.of<void>((k) => { | |
| if (processQueue.length != 0) { | |
| let next = processQueue.shift(); | |
| next.run(k); | |
| return; | |
| } | |
| k(); | |
| })); | |
| }; | |
| function fork(proc: Cont<void>) { | |
| exec(Cont.of((k) => { | |
| processQueue.push( | |
| proc.then((_) => do_(dequeue)) | |
| ); | |
| k(); | |
| })); | |
| } |
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