let bwa = 
  installable_tool 
    Machine.Tool.Default.bwa
    ~url:"http://downloads.sourceforge.net/project/bio-bwa/bwa-0.7.10.tar.bz2"
    ~install_program:(make_and_copy_bin "bwa")
    ~init_program:add_to_dollar_path
    ~witness:(witness_file "bwa")