anchor.diff:  
   ## install minimal set of haskell packages
   RUN apt-get update\
  - && apt-get install -y --force-yes --no-install-recommends\
  + && apt-get install ${OPTS_APT}\
         alex-"${VERSION_ALEX}"\
         cabal-install-"${VERSION_CABAL}"\
         ghc-"${VERSION_GHC}"\
  
positive.code: 
  ## install llvm for the ghc backend
  RUN apt-get update\
   && apt-get install -y --force-yes --no-install-recommends llvm
  
  ## haskell package versions; can be overriden via context hacks
  ENV VERSION_ALEX   3.1.3
  
negative.code: 
  ## disable prompts from apt
  ENV DEBIAN_FRONTEND noninteractive
  
  ## custom apt-get install options
  ENV OPTS_APT        -y --force-yes --no-install-recommends
  
  ## ensure locale is set during build
  ENV LC_ALL          en_US.UTF-8
  