include ..\Utilitys.tlhy


:fib %f !f
    %fr
    [ %n !n
        $n 2 <
        ( [$n]
          [$n 1 - $fr eval $n 2 - $fr eval +] )
        if
    ] !fr

    $f 0 <
    ( ["Error: number is negative"]
      [$f true $fr if] )
    if
;


25 fib ?
msec ?
"End " input