Operators

Namespace: FsToolkit.ErrorHandling.Operator.ResultOption

FsToolkit.ErrorHandling provides the standard infix operators for the map (<!>), apply (<*>), and bind (>>=) functions of the Result<'T option, 'E> type.

In addition to these, it also offers an another infix operator <*^> for usage with normal Result values (without an inner Option). It has the following function signature:

Result<('a -> 'b) option, 'c> -> Result<'a, 'c> 
  -> Result<'b option, 'c>

Examples

Example 1

Assume that we have the following function:

// int -> int -> int -> int
let add a b c = a + b + c

Then using the infix operators, we can do the following:

// Ok (Some 42)
let opResult : Result<int option, string> =
  add
  <!> (Ok (Some 30)) 
  <*> (Ok (Some 10)) 
  <*> (Ok (Some 2)) 

If we have values that are not Option wrapped, we can use the <*^> operator:

let opResult : Result<int option, string> =
  add
  <!> (Ok (Some 30)) 
  <*^> (Ok 10) 
  <*> (Ok (Some 2))

Example 2

The ResultOption.map2 example can be written using the infix operators as below:

let toCreatePostRequest (dto : CreatePostRequestDto) = 

  // Result<Location option, string>
  let locationR = 
    location
    <!> Option.traverseResult Latitude.TryCreate dto.Latitude
    <*> Option.traverseResult Longitude.TryCreate dto.Longitude

  // Result<Tweet, string>
  let tweetR = Tweet.TryCreate dto.Tweet

  // Result<CreatePostRequest, string>
  Result.map2 createPostRequest tweetR locationR