map

Namespace: FsToolkit.ErrorHandling

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

Function Signature

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

Examples

Take the following functions for example

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

Example 1

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

// task { Ok 277 }

Example 2

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

// task { Error ["bad things happened"] }