Comment by munchler

I'm more familiar with F#, so I got stuck at this line:

    type ('a,'b) app += List_name : 'a list -> ('a,list_name) app

I understand that app is an extensible type and this line adds a union case called List_name to the type, but the signature of List_name confuses me. If I write (List_name x) is x a list or a function?