mapErrors

CancellableTaskValidation.mapErrors

Namespace: FsToolkit.ErrorHandling

Function Signature:

('errorInput list -> 'errorOutput list)
  -> CancellableTaskValidation<'ok, 'errorInput>
  -> CancellableTaskValidation<'ok, 'errorOutput>

Applies a mapping function to the entire error list inside a CancellableTaskValidation. If the computation is Ok, the mapping function is not called and the value is propagated unchanged.

Note: mapErrors operates on the whole list at once. To map over individual errors, use mapError.

Examples

Example 1

Deduplicating errors before returning them:

let validateInput (input: FormInput) : CancellableTaskValidation<ValidatedForm, string> =
    runValidation input
    |> CancellableTaskValidation.mapErrors List.distinct

Example 2

Sorting and limiting the number of errors returned to a caller:

let validateOrder (order: Order) : CancellableTaskValidation<ValidatedOrder, string> =
    runOrderValidation order
    |> CancellableTaskValidation.mapErrors (fun errs -> errs |> List.sort |> List.truncate 5)

Example 3

Converting a list of typed errors to a list of user-facing messages:

let processRequest (req: Request) : CancellableTaskValidation<Response, string> =
    validateRequest req
    |> CancellableTaskValidation.mapErrors (List.map (fun (e: DomainError) -> e.UserMessage))