traverseAsync

Option.traverseAsync

Namespace: FsToolkit.ErrorHandling

Function Signature:

('a -> Async<'b>) -> 'a option -> Async<'b option>

Note that traverse is the same as map >> sequence. See also Option.sequenceAsync.

See also Scott Wlaschin's Understanding traverse and sequence.

Examples

Example 1

Let's assume we have a type Customer:

type Customer = {
  Id : int
  Email : string
}

And we have a function called getCustomerByEmail that retrieves a Customer by email address asynchronously from some external source -- a database, a web service, etc:

// string -> Async<Customer>
let getCustomerByEmail email : Async<Customer> = async {
    return { Id = 1; Email = "[e-mail]" } // return a constant for simplicity
}

If we have a value of type string option and want to call the getCustomerByEmail function, we can achieve it using the traverseAsync function as below:

Some "[e-mail]" |> Option.traverseAsync getCustomerByEmail
// async { return Some { Id = 1; Email = "[e-mail]" } }

None |> Option.traverseAsync getCustomerByEmail
// async { return None }