func decimal(args ...interface{}) Validation {
	return func(value interface{}, builders ...interface{}) (interface{}, interface{}) {
		if value == nil || value == "" {
			return value, nil
		}
		switch v := value.(type) {
		case float64:
			return v, nil
		case string:
			if f, err := strconv.ParseFloat(v, 64); err == nil {
				return f, nil
			}
			return nil, errors.New("NOT_DECIMAL")
		default:
			return nil, errors.New("FORMAT_ERROR")
		}
	}
}
decimal - check that validated value is decimal number.
package livr
import (
	"errors"
	"strconv"
)