Namespace: FsToolkit.ErrorHandling.Operator.Result

FsToolkit.ErrorHandling provides the standard infix operators for the map (<!>), apply (<*>), and bind (>>=) functions of the Result type.


Example 1

The example that we saw in the Result.map3 can be solved using the map and apply operators as below:

open FsToolkit.ErrorHandling.Operator.Result

let opResult =
  <!> tryParseInt "35"
  <*> tryParseInt "5"
  <*> tryParseInt "2"

Let's assume that we want to implement a function, tryParseEvenInt, which parses a string to an integer only if the string represents an even integer. We can implement it using the bind operator as below:

// int -> Result<int, string>
let evenInt x =
  if x % 2 = 0 then
    Ok x 
    Error (sprintf "%d is not a even integer" x)

// string -> Result<int,string>
let tryParseEvenInt str =
  tryParseInt str
  >>= evenInt

tryParseEvenInt "42" // Ok 42
tryParseEvenInt "41" // Error "41 is not a even integer"
tryParseEvenItn "foo" // Error "Unable to parse 'foo' to integer"

Note that >>= is just a shortcut for |> Result.bind:

let tryParseEvenInt str =
  tryParseInt str
  |> Result.bind evenInt

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