map

Namespace: FsToolkit.ErrorHandling

map applies a transformation to the value inside a Validation if it represents a successful result (Ok). It allows you to perform a computation on the value while preserving the success/error status of the original Validation. If the original Validation is an Error, map does nothing and returns the same Error unchanged.

Function Signature

('okInput -> 'okOutput) -> Validation<'okInput, 'error> -> Validation<'okOutput, 'error>

Examples

Take the following functions for example

// string -> int
let remainingCharacters (prompt: string) =
    280 - prompt.Length

Example 1

let validation =
    Validation.ok "foo" // Validation<string, string>
    |> Validation.map remainingCharacters // Validation<int, string>

// Ok 277

Example 2

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

// Error ["bad things happened"]