func GetLens(name string) (Lens, error) {
	lens, ok := lensReg[name]
	if !ok {
		return nil, ErrInvalidLensName
	}
	return lens, nil
}
func GetLens(name string) (Lens, error) {
	lens, ok := lensReg[name]
	if !ok {
		return nil, ErrInvalidLensName
	}
	return lens, nil
}
func GetLens ( name string ) ( Lens , error ) { lens , ok := lensReg [ name ] if ! ok { return nil , ErrInvalidLensName } return lens , nil }
// GetLens returns a Lens by name, if it exists; otherwise it returns an error.
GetLens returns a Lens by name if it exists ; otherwise it returns an error .