LazyList

SampleLazyList.fs

// see also. https://gist.github.com/1430157

open Microsoft.FSharp.Collections

let distanceOfSameValueElements xs =
    let rec loop i dict xs =
        let x = LazyList.head xs
        match Map.tryFind x dict with
        | None   -> loop (i + 1) (Map.add x i dict) (LazyList.tail xs)
        | Some j -> i - j
    loop 0 Map.empty (LazyList.ofSeq xs)