A F# tail-recursive question

Posted by ksharp on Stack Overflow See other posts from Stack Overflow or by ksharp
Published on 2010-06-01T08:21:40Z Indexed on 2010/06/01 8:23 UTC
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Recently, I'm learning F#. I try to solve problem in different ways. Like this:

(*

[0;1;2;3;4;5;6;7;8] -> [(0,1,2);(3,4,5);(6,7,8)]

*)

//head-recursive
let rec toTriplet_v1 list=
    match list with
    | a::b::c::t -> (a,b,c)::(toTriplet_v1 t) 
    | _ -> []

//tail-recursive
let toTriplet_v2 list=
    let rec loop lst acc=
        match lst with
        | a::b::c::t -> loop t ((a,b,c)::acc)
        | _ -> acc
    loop list []

//tail-recursive(???)
let toTriplet_v3 list=
    let rec loop lst accfun=
        match lst with
        | a::b::c::t -> loop t (fun ls -> accfun ((a,b,c)::ls))
        | _ -> accfun []
    loop list (fun x -> x)

let funs = [toTriplet_v1; toTriplet_v2; toTriplet_v3];
funs |> List.map (fun x -> x [0..8]) |> List.iteri (fun i x -> printfn "V%d : %A" (i+1) x)

I thought the results of V2 and V3 should be the same. But, I get the result below:

V1 : [(0, 1, 2); (3, 4, 5); (6, 7, 8)]
V2 : [(6, 7, 8); (3, 4, 5); (0, 1, 2)]
V3 : [(0, 1, 2); (3, 4, 5); (6, 7, 8)]

Why the results of V2 and V3 are different?

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