beginningOfLine: true,
		macros:          predefine(flags.D),
	}
}

// predefine installs the macros set by the -D flag on the command line.
func predefine(defines flags.MultiFlag) map[string]*Macro {
	macros := make(map[string]*Macro)
	for _, name := range defines {
		value := "1"
		i := strings.IndexRune(name, '=')
		if i > 0 {
			name, value = name[:i], name[i+1:]
		}