map

Namespace: FsToolkit.ErrorHandling

map applies a transformation to the value inside a Result 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 Result. If the original Result is an Error, map does nothing and returns the same Error unchanged.

Function Signature

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

Examples

Take the following functions for example

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

Example 1

let result =
    Ok "foo" // Result<string, string>
    |> Result.map remainingCharacters // Result<int, string>

// Ok 277

Example 2

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

// Error "bad things happened"