Operators

Result Infix Operators

Namespace: FsToolkit.ErrorHandling.Operator.Result

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

Examples

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 =
add
<!> 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
else
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