title: Equivalent of "pip install -U -r requirements.txt" for Cabal?
body: <p>In Python there's a <code>pip install -U -r requirements.txt</code> mantra to get all packages in version listed in file <code>requirements.txt</code> installed, typically in virtualenv.</p>
  
  <p>Is there something similar in Cabal / Haskell? After all, cabal seems to have <code>cabal list --installed</code> which makes it theoretically possible to do a similar thing for a cabal sandbox.</p>