flatten

flatten.fsx

type 'a Node =
    | One of 'a
    | Many of 'a Node list

let testList = [ One "a" ; Many [ One "b" ; Many [ One "c" ; One "d" ] ; One "e" ] ]


let rec flatten (list: 'a Node list) : 'a list = 
    let rec flatten_nodes acc (node: 'a Node list) : 'a list = 
        match node with 
        | []            -> acc
        | One(n)::ns    -> n :: flatten_nodes acc ns
        | Many(n)::ns   -> flatten_nodes (flatten_nodes acc n) ns
        
    flatten_nodes [] list
    
flatten testList