joanllenas / ts.data.maybe Goto Github PK

This is a very nice library. But one issue I came across was the fact that isNothing and isJust are defined as:

typescript
export declare const isJust: (value: Maybe) => boolean;
export declare const isNothing: (value: Maybe) => boolean;

...when it would be much better if they were defined as:

```typescript
export declare const isJust: <T>(value: Maybe<T>) => value is Just<T>;
export declare const isNothing: <T>(value: Maybe<T>) => value is Nothing;

This would allow type narrowing. Unfortunately, I can't write these myself because of another issue which is that you don't export the types for Just and Nothing. So they can't be referred to outside the package. I realized that I can use caseOf as well to narrow types, sometimes it is better to do this in an imperative vs. functional way (although I appreciate the option).