traverseResult

FsToolkit.ErrorHandling

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Result

traverseResult

Option.traverseResult
Namespace: FsToolkit.ErrorHandling
Function Signature:
('a -> Result<'b,'c>) -> 'a option -> Result<'b option, 'c>
Note that traverse is the same as map >> sequence. See also Option.sequenceResult.
See also Scott Wlaschin's Understanding traverse and sequence.
Examples
Example 1
If we have a value of type string option and want to call the tryParseInt function that we defined in the Result.map2 example, we can achieve it using the traverseResult function as below:
Some "42" |> Option.traverseResult tryParseInt
// Ok (Some 42)
​
None |> Option.traverseResult tryParseInt
// Ok None
​
Some "foo" |> Option.traverseResult tryParseInt
// Error "unable to parse 'foo' to integer"
Example 2
The CreatePostRequest type that we defined in Result.map3 example contains a Location option. The corresponding DTO objects would look like this:
type LocationDto = {
  Latitude : float
  Longitude : float
}
​
type CreatePostRequestDto = {
  Tweet : string
  Location : LocationDto option
}
Let's assume that we have this function to convert a LocationDto to a Location:
// LocationDto -> Result<Location, string>
let locationFromDto (dto : LocationDto) = result {
  let! lat = Latitude.TryCreate dto.Latitude
  let! lng = Longitude.TryCreate dto.Longitude
  return {Location.Latitude = lat; Longitude = lng}
}
Then in order to create a similar function to convert a CreatePostRequestDto to a CreatePostRequest, we can make use of traverseResult as below:
let createPostRequestFromDto (dto : CreatePostRequestDto) = result {
    // Parse the location DTO option to a Location option,
    // returning an error if it's Some and invalid
    let! location =
      dto.Location |> Option.traverseResult locationDtoToLocation
​
    let! tweet = Tweet.TryCreate dto.Tweet
    return {
      Tweet = tweet
      Location = location
    }
  }
See also the example 2 of ResultOption.map2.

Option

sequenceResult

Last modified 9mo ago

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Outline

Option.traverseResult

Examples