Last updated 3 months ago

Result Infix Operators

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

Namespace: FsToolkit.ErrorHandling.Operator.Result


Example 1

The example that we saw in the Result.map3 can be solved using the map & 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 contains a 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" // returns - Ok 42
tryParseEvenInt "41" // returns - Error "41 is not a even integer"
tryParseEvenItn "foo" // returns - Error "Unable to parse 'foo' to integer"

Note: The tryParseEvenInt can be return using the bind function as follow

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