let print (text : string) offset =
    text.ToCharArray() 
    |> Array.mapi (fun i c -> (i, c))
    |> Seq.groupBy (fun (i, _) -> i % offset)
    |> Seq.map (fun (_, s) -> s |> Seq.map (fun (_, c) -> c.ToString()) |> Seq.reduce (fun c1 c2 -> c2 + "|" + c1))
    |> Seq.iter (fun str -> printfn "%s" str)

print "床前明月光疑似地上霜举头望明月低头思故乡" 5

//低|举|疑|床
//头|头|似|前
//思|望|地|明
//故|明|上|月
//乡|月|霜|光