Recursion & Immutability in F#

Question

Consider the following simplistic example:

type Parent = { Children : Child list }
and Child = { Value : int ; Parent : Parent }

let rec children = [ { Value = 0 ; Parent = parent } ]
and parent = { Children = children }

The F# compiler is smart enough to correctly initialize these recursive objects, as can be verified by running

obj.ReferenceEquals(parent, parent.Children.Head.Parent)

Now, consider the following generalization:

let length = 100 // assume arbitrary

let rec children = List.init length (fun i -> { Value = i ; Parent = parent })
and parent = { Children = children }

This definition will result in a compiler error. My question is the following: is there any way I could make the above binding without resorting to reflection or mutable fields?

Answer 1

let rec mkChild i = {Value = i; Parent = parent}
and parent = { Children = children }
and children = List.init length mkChild