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The O.filter function doesn't have an overload that takes type guards into account. The only definition that exists looks like this:
export declare function filter<A>(predicateFn: (value: A) => boolean): (option: Option<A>) => Option<A>;Compare this to A.filter which has an overload that allows for a type guard to be passed in:
export declare function filter<A, B extends A>(predicateFn: (value: A) => value is B): (xs: Array<A>) => Array<B>;It would be nice to have the same for O.filter.
Here's an example that currently fails:
type WithOrWithoutYou = {type: 'with', you: string} | {type: 'without'};
declare const withOrWithout: WithOrWithoutYou;
pipe(
O.some(withOrWithout),
O.filter(w => w.type === 'with'),
O.map(w => w.you), // <--- Fails with: Property 'you' does not exist on type 'WithOrWithoutYou'.
)Thanks for a great library! 🙌
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