This is applicative, collecting all errors. Compare the example below with .
See also Scott Wlaschin's .
Examples
Example 1
// string -> Result<int, string>
let tryParseInt str =
match Int32.TryParse str with
| true, x -> Ok x
| false, _ -> Error $"unable to parse '{str}' to integer"
["1"; "2"; "3"]
|> Seq.map tryParseInt
|> Seq.sequenceResultA
// Ok [| 1; 2; 3 |]
["1"; "foo"; "3"; "bar"]
|> Seq.map tryParseInt
|> Seq.sequenceResultA
// Error [| "unable to parse 'foo' to integer"
// "unable to parse 'bar' to integer" |]
Example 2
// int -> Result<bool, string>
let isPrime (x: int) =
if x < 2 then Error $"{x} must be greater than 1"
elif x = 2 then Ok true
else
let rec isPrime' (x : int) (i : int) =
if i * i > x then Ok true
elif x % i = 0 then Ok false
else isPrime' x (i + 1)
isPrime' x 2
// seq<int> -> Result<bool, string[]>
let checkIfAllPrime (numbers: seq<int>) =
seq { for x in numbers -> isPrime x } // Result<bool, string> seq
|> Seq.sequenceResultA // Result<bool[], string[]>
|> Result.map (Seq.forall id) // shortened version of '|> Result.map (fun results -> results |> Array.forall (fun x -> x = true))'
let a = [| 1; 2; 3; 4; 5 |] |> checkIfAllPrime
// Error [| "1 must be greater than 1" |]
let b = [ 1; 2; 3; 4; 5; 0 ] |> checkIfAllPrime
// Error [| "1 must be greater than 1"; "0 must be greater than 1" |]
let a = seq { 2; 3; 4; 5 } |> checkIfAllPrime
// Ok false
let a = seq { 2; 3; 5 } |> checkIfAllPrime
// Ok true
