let cufflinks =
  let url = 
    "http://cole-trapnell-lab.github.io/cufflinks/assets/downloads/cufflinks-2.2.1.Linux_x86_64.tar.gz" in
  let witness = witness_file "cufflinks" in
  let install_program ~path = KEDSL.Program.(shf "cp * %s" path) in
  installable_tool Machine.Tool.Default.cufflinks ~install_program ~url 
    ~init_program:add_to_dollar_path ~witness