Question

Let’s say I have a discriminated union:

type foo = Bar | Baz | Batz

Then, I want to check how many members of a list are of type Baz:

List.sumBy (function Bar -> 1 | _ -> 0) foos

Is there a more idiomatic way to do this?

Answer 1

Notice that your example is incorrect. It should be:

List.sumBy (fun x -> match x with Baz -> 1 | _ -> 0) foos

which could be rewritten as:

List.sumBy (function Baz -> 1 | _ -> 0) foos

I don’t think there’s a more idomatic way than using List.sumBy here.