The definition of list is: type 'a list = [] | (::) of 'a * 'a list When you write a list like: [x; y; z] This is syntactic sugar for: x::y::z::[] W

The definition of list is: type 'a list = [] | (::) of 'a * 'a list When you write a list like: [x; y; z] This is syntactic sugar for: x::y::z::[] Which is syntactic sugar for: (::) (x, (::) (y, (::) (z, []))) One can imagine using more ordinary constructor names instead: type 'a list = Nil | Cons of 'a * 'a list And then the above would be: Cons (x, Cons (y, Cons (z, Nil))) In OCaml, data constructor names mar be either a capital letter followed by set or more capital/lower letters/underscores/apostrophes/digits, or one of the following: [] () true false (::) Type directed constructor disambiguating means you can do funky things like: type 'a nonempty = (::) of 'a * 'a list And write such a value just like you would a normal list.