mapErrors

Namespace: FsToolkit.ErrorHandling

Similar to Validation.mapError, except that the mapping function is passed the full list of errors, rather than each one individually.

Function Signature

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

Examples

Take the following functions for example

// string -> int
let getErrorCode (messages: string list) =
    match messages |> List.tryFind ((=) "bad things happened") with
    | Some _ -> [1]
    | _ -> [0]

Example 1

let result =
    Validation.ok "all good" // Validation<string, string>
    |> Validation.mapErrors getErrorCode // Validation<string, int>

// Ok "all good"

Example 2

let result : Validation<string, int> =
    Validation.error "bad things happened" // Validation<string, string>
    |> Validation.mapErrors getErrorCode // Validation<string, int>

// Error [1]