[request for help] - casting right type on left #251
Description
I'm new to functional programming and I am probably doing this all wrong.
I very much like using Either to pass errors up the call chain.
In practice, I find myself using a type cast of the right side when the either is a Left very often which feels wrong.
This typically happens when a function in the middel of the call chain catches a left from a function down the chain that has a different Right type than the function itself.
I assume there must be a better way of doing this otherwise the cast function would probably be part of the library.
What is the better way ?
Here's an simplified example
function castRight_of_Left<RT>(either: Either<Error, unknown>) {
return Left<Error, RT>(either.left())
}
public async getOrder(orderNumber: string): Promise<Either<Error, Order>> {
let result = await this._orderRepo.getOrderByOrderNumber(orderNumber) // returns Promise<Either<Error, Order | null>>
if (result.isLeft()) return castRight_of_Left<Order_and_Sample>(result) // Database error, pass the error up the call chain
if (getSampleresult.right() == null) return Left(new Error(`order not found`)) // aanvraag niet gevonden
const order = result.right()!
// ... manipulations of the order object
return Right(order)
}