anchor.diff:   && apt-get install ${OPTS_APT}\
         ghc-"${VERSION_GHC}"
   
  -## set the VERSION vars and PATH for login shells
  -RUN\
  -  ( exec >> /etc/profile.d/haskell.sh\
  - && echo "VERSION_ALEX=${VERSION_ALEX}"\
  - && echo "VERSION_CABAL=${VERSION_CABAL}"\
  - && echo "VERSION_HAPPY=${VERSION_HAPPY}"\
  - && echo "VERSION_GHC=${VERSION_GHC}"\
  - && echo 'PATH=${HOME}/.cabal/bin:${PATH}'\
  -  )
  -
   ## link the binaries into /usr/local/bin
   RUN find /opt -maxdepth 3 -name bin -type d\
     -exec sh -c\
  
positive.code: ## Dockerfile for a haskell environment
  ## https://github.com/darinmorrison/docker-haskell
  FROM       phusion/baseimage:0.9.12
  MAINTAINER Darin Morrison <darinmorrison+docker@gmail.com>
  
  ## disable prompts from apt
  
negative.code: ENV OPTS_APT        -y --force-yes --no-install-recommends
  
  ## ensure locale is set during build
  ENV LC_ALL          C.UTF-8
  ENV LANG            C.UTF-8
  ENV LANGUAGE        C.UTF-8
  
  ## ensure locale is set for new logins
  RUN echo    'LC_ALL=C.UTF-8' >> '/etc/default/locale'\
   && echo      'LANG=C.UTF-8' >> '/etc/default/locale'\
   && echo  'LANGUAGE=C.UTF-8' >> '/etc/default/locale'
  
  ## add ppa for ubuntu trusty haskell packages
  RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys F6F88286\
   && echo 'deb     http://ppa.launchpad.net/hvr/ghc/ubuntu trusty main' >> /etc/apt/sources.list.d/haskell.list\
   && echo 'deb-src http://ppa.launchpad.net/hvr/ghc/ubuntu trusty main' >> /etc/apt/sources.list.d/haskell.list
  
  ## haskell package versions; can be overriden via context hacks
  ENV VERSION_ALEX   3.1.3
  