mapError

Namespace: FsToolkit.ErrorHandling

mapError takes a validation and a normal function and returns a new validation value based on the input error value and the function

Function Signature

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

Examples

Take the following functions for example

// string -> int
let getErrorCode (message: string) =
    match message with
    | "bad things happened" -> 1
    | _ -> 0

Example 1

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

// Ok "all good"

Example 2

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

// Error [1]