Option Explicit

Sub SetCrvLength

  Dim crv, lold, lnew, dom, pts, t

  crv = Rhino.GetCurveObject("Select curve to set length", 4, True)
  If Not IsArray(crv) Then Exit Sub

  If Rhino.IsCurveClosed(crv(0)) Then
    Rhino.Print "Cannot set the length of closed curves."
    Exit Sub
  End If

  lold = Rhino.CurveLength(crv(0))
  lnew = Rhino.GetReal("New curve length", lold, 0.0, lold)
  If Not IsNumeric(lnew) Then Exit Sub
  If (lnew <= 0) Or (lnew >= lold) Then Exit Sub

  dom = Rhino.CurveDomain(crv(0))
  If (dom(1)-crv(4)) < (crv(4)-dom(0)) Then
    Rhino.ReverseCurve crv(0)
    dom = Rhino.CurveDomain(crv(0))
  End If

  pts = Rhino.DivideCurveLength(crv(0), lnew)
  t = Rhino.CurveClosestPoint(crv(0), pts(1))
  Rhino.TrimCurve crv(0), Array(dom(0), t), True

End Sub