Recursive records in F#

Question

A friend and I are reading up on F# and are messing around with records at the moment.

We have made the following record for representing a person:

t         


        

Answer 1

If you declare father and mother as Parent option then you can use it like:

let f = { name = "Father"; father = None; mother = None }
let m = { name = "Mother"; father = None; mother = None }
let c = { name = "Child"; father = Some(f); mother = Some(m) }

without using Parent option for father and mother you would have to create a "null parent" instance and use that instead of None.

Answer 2

Lee shows a more useful definition, but you can create an instance of your Person type:

let rec loopy = { name = "loopy"; father = loopy; mother = loopy }

or

let rec male = { name = "male"; father = male; mother = female }
  and female = { name = "female"; father = male; mother = female}

Of course, these aren't at all helpful if you're modeling real people, but the compiler doesn't know that. A similar recursive type could be useful if you're trying to define a cycle, for instance.