func Parse(regexp string) (Regexp, error) {
	pt, err := syntax.Parse(regexp, syntax.Perl)
	if err != nil {
		return Regexp{}, err
	}
	pt = pt.Simplify()
	return Regexp{pt: pt}, nil
}
Parse takes a regexp in Perl syntax (as implemented by regexp/syntax) and
returns a Regexp, for introspecting the regexp.
package regexputil
import (
	"regexp/syntax"
)
type Regexp struct {
	pt *syntax.Regexp
}