gistfile1.txt

type Animal() = class end

type Dog() = inherit Animal()

let feed (animals: seq<Animal>) = ()

feed [ Dog(); Animal() ]

This works indeed, but unfortunately it prevents other use cases which would be allowed by using seq<#Animal>:

type Animal(name: string) = class end

type Dog(name: string) = inherit Animal(name)

let feed (animals: seq<Animal>) = ()

let myDogs = List.map Dog ["Lassie"; "Rex"]
feed myDogs
// the type 'Dog list' is not compatible with the type 'seq<Animal>'

unless we open the can of worms of co/contravariant type parameters :-)

But

let myDogs:seq<Animal> = [ Dog(); Animal() ]

doesn't compile and I find that highly irritating