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mod.ts
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mod.ts
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// deno-lint-ignore-file no-explicit-any
export interface Computation<T> {
[Symbol.iterator](): Iterator<Control, T, any>;
}
export interface Continuation<T = unknown, R = unknown> {
(value: T extends void ? void : T): Computation<R>;
}
export type Result<T> = { ok: true; value: T } | { ok?: false; error: Error };
export type Control =
| {
type: "shift";
block(k: Continuation, reject: Continuation<Error>): Computation<unknown>;
}
| {
type: "reset";
block(): Computation<unknown>;
}
| {
type: "resume";
result: Result<unknown>;
iter: Iterator<Control, unknown>;
};
export function* reset<T>(block: () => Computation<any>): Computation<T> {
return yield { type: "reset", block };
}
export function* shift<T, R = unknown>(
block: (
k: Continuation<T, R>,
reject: Continuation<Error>,
) => Computation<any>,
): Computation<T> {
return yield { type: "shift", block };
}
export function evaluate<T>(block: () => Computation<unknown>) {
let stack: Iterator<Control, unknown, any>[] = [];
let iter = block()[Symbol.iterator]();
let current = $next(undefined);
while (true) {
let result = safe(() => current(iter));
if (!result.ok) {
if (stack.length > 0) {
iter = stack.pop()!;
current = $throw(result.error);
} else {
throw result.error;
}
} else {
let next = result.value;
if (next.done) {
if (stack.length > 0) {
iter = stack.pop()!;
current = $next(next.value);
} else {
return next.value as T;
}
} else {
const control = next.value;
if (control.type === "reset") {
stack.push(iter);
iter = control.block()[Symbol.iterator]();
} else if (control.type === "shift") {
const continuation = iter;
let resolve = oneshot((value: unknown) => ({
type: "resume",
iter: continuation,
result: { ok: true, value },
}));
let reject = oneshot((error: Error) => {
return { type: "resume", iter: continuation, result: { error } };
});
iter = control.block(resolve, reject)[Symbol.iterator]();
} else {
iter = control.iter;
let { result } = control;
current = result.ok ? $next(result.value) : $throw(result.error);
}
}
}
}
}
function $next(value: unknown) {
return (iter: Iterator<Control, unknown, unknown>) => iter.next(value);
}
function $throw(error: Error): ReturnType<typeof $next> {
return (iter) => {
if (iter.throw) {
return iter.throw(error);
} else {
throw error;
}
};
}
function safe<T>(fn: () => T): Result<T> {
try {
return { ok: true, value: fn() };
} catch (error) {
return { error };
}
}
function oneshot<TArg, T>(
fn: (arg: TArg) => Control,
): (arg: TArg) => Computation<T> {
let computation: Computation<T> | undefined = undefined;
return function k(arg: TArg) {
if (!computation) {
let control = fn(arg);
let iterator: Iterator<Control, T> = {
next() {
iterator.next = () => ({
done: true,
value: undefined as unknown as T,
});
return { done: false, value: control };
},
};
computation = { [Symbol.iterator]: () => iterator };
}
return computation;
};
}