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Result.ts
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177 lines (161 loc) · 3.59 KB
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export enum Status {
/**
* The Result has completed, but an error has occurred
*/
Failed,
/**
* The Result has completed, and the data is available
*/
Ok,
/**
* The Result is currently waiting to complete
*/
Pending,
/**
* The Result is currently waiting to complete, but stale data is available
*/
Stale,
}
/**
* The Result has completed, but an error has occurred
*/
export interface Failed<E extends Error> {
_tag: Status.Failed;
/**
* The error that has occurred
*/
error: E;
}
export interface Ok<D> {
_tag: Status.Ok;
/**
* The data that was fetched
*/
data: D;
}
export interface Pending {
_tag: Status.Pending;
}
export interface Stale<D> {
_tag: Status.Stale;
/**
* The stale data that is being replaced
*/
data: D;
}
/**
* Data in various asynchronous states.
*/
export type Result<D, E extends Error = Error> =
| Failed<E>
| Ok<D>
| Pending
| Stale<D>;
/**
* Creates a `Result` in the `Failed` state.
*/
export function failed<E extends Error = Error>(error: E): Failed<E> {
return { _tag: Status.Failed, error };
}
/**
* Creates a `Result` in the `Ok` state.
*/
export function ok<D>(data: D): Ok<D> {
return { _tag: Status.Ok, data };
}
/**
* Creates a `Result` in the `Pending` state.
*/
export function pending(): Pending {
return { _tag: Status.Pending };
}
/**
* Creates a `Result` in the `Stale` state.
*/
export function stale<D>(data: D): Stale<D> {
return { _tag: Status.Stale, data };
}
/**
* Map over the data of a `Result` that is in the Ok or Stale states
*/
export function map<D, R>(
fn: (data: D) => R,
): <E extends Error = Error>(result: Result<D, E>) => Result<R, E> {
return (result) => {
if (result._tag === Status.Ok || result._tag === Status.Stale) {
return {
_tag: result._tag,
data: fn(result.data),
};
}
return result;
};
}
/**
* Match over the Result
*/
export function match<D, R, E extends Error = Error>(
onFailure: (error: E) => R,
onPending: () => R,
onOk: (data: D) => R,
onStale: (data: D) => R,
): (result: Result<D, E>) => R;
export function match<D, R, E extends Error = Error>(
onFailure: (error: E) => R,
onPending: () => R,
onOk: (data: D, isStale: boolean) => R,
): (result: Result<D, E>) => R;
export function match<D, R, E extends Error = Error>(
onFailure: (error: E) => R,
onPending: () => R,
onOk: (data: D, isStale: boolean) => R,
onStale?: (data: D) => R,
): (result: Result<D, E>) => R {
return (result) => {
if (isFailed(result)) {
return onFailure(result.error);
} else if (isPending(result)) {
return onPending();
} else if (isStale(result)) {
if (onStale) {
return onStale(result.data);
} else {
return onOk(result.data, true);
}
} else {
return onOk(result.data, false);
}
};
}
/**
* Determine if a `Result` is a `Failed`
*/
export function isFailed<D, E extends Error = Error>(
result: Result<D, E>,
): result is Failed<E> {
return result._tag === Status.Failed;
}
/**
* Determine if a `Result` is an `Ok`
*/
export function isOk<D, E extends Error = Error>(
result: Result<D, E>,
): result is Ok<D> {
return result._tag === Status.Ok;
}
/**
* Determine if a `Result` is a `Pending`
*/
export function isPending<D, E extends Error = Error>(
result: Result<D, E>,
): result is Pending {
return result._tag === Status.Pending;
}
/**
* Determine if a `Result` is a `Stale`
*/
export function isStale<D, E extends Error = Error>(
result: Result<D, E>,
): result is Stale<D> {
return result._tag === Status.Stale;
}