default do
  Environment.new(echo: :command) do |env|
    env.append('CPPPATH' => glob('src/**'))
    env.add_build_hook do |builder|
      if builder.name == "Object" && builder.sources.first =~ %r{one\.c}
        builder.vars["CFLAGS"] << "-O1"
        builder.sources = ['src/two/two.c']
      elsif builder.name == "Object" && builder.target =~ %r{two\.o}
        new_vars = builder.vars.clone
        new_vars["CFLAGS"] << "-O2"
        builder.vars = new_vars
      end
    end
    env.Object('one.o', 'src/one/one.c')
    env.Object('two.o', 'src/two/two.c')
  end
end