Add vertical space only if there is no pagebreak

Question

I'd like to define a new listings environment where the listing has an \hrule before and after the listing itself. In order to do this I've defined this environment:

\lstnewenvironment{haskell}[1][]
    {
        \vspace{0.4cm}
        \mathligsoff
        \hrule
        \lstset{language=haskell, basicstyle=\small, #1}
    }{
        \hrule
        \mathligson
        \vspace{0.4cm}
}

The problem is that sometimes, when a listing ends up at the bottom of a page, the closing \hrule moves to the next page:

As you can see the highlighted rule ended up at the start of the new page, which is just ugly.

How can I avoid to produce a pagebreak between the listing and the rule at the end? I have already tried to add a \nopagebreak before \hrule but it didn't solve the problem.

Answer 1

Like indicated in the comments by Jubobs I'd use tcolorbox for this. The following code mimicks the layout outlined in the question but with tcolorbox a lot fancier layouts easily are possible.

\documentclass{article}
\usepackage{tcolorbox,listings}
\tcbuselibrary{listings,xparse}
\tcbset{listing engine=listings}

\NewTCBListing{haskell}{O{}}{%
  % colors:
  colback = white , colframe = black , coltitle = black ,
  % rules:
  boxrule = 0pt , toprule = 1pt , bottomrule = 1pt , arc = 0pt ,
  % spacing:
  boxsep = 0pt , left = 0pt , right = 0pt ,
  % listing options:
  listing options = {
    language = haskell ,
    basicstyle = \small ,
    gobble = 2 ,%
    #1%
  } ,
  listing only
}

\begin{document}

\begin{haskell}
  sums = zipWith (\x y -> x + y) numbers1 numbers2
  products = zipWith (\x y -> x * y) numbers1 numbers2
  pairs = zipWith (\x y -> (x, y)) numbers1 numbers2
\end{haskell}

\end{document}

Unless you specify the breakable option of tcolorbox (needs the breakable library) the complete listing will stay on one page.