F#: pattern matching on base types - f#

Question

I have a series of validation functions I want to put into an array to execute:
type result = {D: int; E: int; F: int; G: int}
type InvalidReason =
| AAA
| BBB
| CCC
| DDD
| EEE
type Validation =
| Valid
| Invalid of InvalidReason
let validators = [|AAA; BBB; CCC; DDD; EEE|]
let validateStuff result =
validators
|> Array.map(fun v -> v result)
|> Array.contains(Validation.Invalid _)
The problem is that last line of code. I am getting an "Unexpected value _ in the expression." The following does work
|> Array.contains(Validation.Valid)
|> Array.contains(Validation.Invalid InvalidReason.AAA)
But I don't want to spell out each of the sub types for InvalidReasons. Is there some syntax I am overlooking?

Answer 1

The function Array.contains takes a value and checks if that value is in the array. What you're trying to do is to give it a whole bunch of values to check. Well, this won't work: the function only takes one. And it doesn't help that there is no syntax like that in F# :-)
You might use another function that takes multiple values, but a better way to accomplish what you want is to use a function that takes a predicate - Array.exists. Make yourself a predicate to check if a value is "invalid":
let isInvalid x = match x with
| Valid -> false
| Invalid _ -> true
And pass it to Array.exists:
let validateStuff result =
validators
|> Array.map(fun v -> v result)
|> Array.exists isInvalid
Or you could even put that function inline:
let validateStuff result =
validators
|> Array.map(fun v -> v result)
|> Array.exists ( fun x -> match x with
| Valid -> false
| Invalid _ -> true )
Or even shorter, using the function keyword:
let validateStuff result =
validators
|> Array.map(fun v -> v result)
|> Array.exists ( function | Valid -> false | Invalid _ -> true )
Or even shorter, getting rid of as much noise as possible:
let validateStuff result =
validators
|> Array.map(fun v -> v result)
|> Array.exists ( function Invalid _ -> true | _ -> false )