Is it possible to pass discriminated union tags as arguments?

Question

Is it possible to pass the type of a discriminated union tag to another function so it can use it for pattern matching?

Non working example of what I mean:

Answer 1

Just for completeness, I'll list this solution.
If you quoted your input, you'd be able to reason about the names of the tags:

open Microsoft.FSharp.Quotations

type Animal = Pig of string | Cow of string | Fish of string

let isAnimal (animalType : Expr) (animal : Expr) =
    match animal with
        | NewUnionCase(at, _) ->
            match animalType with
                | Lambda (_, NewUnionCase (aatt, _)) -> aatt.Name = at.Name
                | _ -> false
        | _ -> false

let animal = <@ Pig "Mike" @>
isAnimal <@ Pig @> animal  // True
isAnimal <@ Cow @> animal  // False

This is admittedly quite verbose though, and it would become even more so if you wanted to quote a list instead of a single value.

A slightly different version, where we quote only the animal type, would let you easily filter lists of animals, as you need (at the price of some questionable comparison of strings):

open Microsoft.FSharp.Quotations

type Animal = Pig of string | Cow of string | Fish of string

let isAnimal (animalType : Expr) animal =
    match animalType with
        | Lambda (_, NewUnionCase (aatt, _)) -> animal.ToString().EndsWith(aatt.Name)
        | _ -> false

let animal = Pig "Mike"  // No quote now, so we can process Animal lists easily
isAnimal <@ Pig @> animal  // True
isAnimal <@ Cow @> animal  // False

let animals = [Pig "Mike"; Pig "Sarah"; Fish "Eve"; Cow "Laura"; Pig "John"]
let pigs = animals |> List.filter (isAnimal <@ Pig @>)

The latter version is not really superior to passing the tag name as a string.