add all validator, simplify error messages

length.go

@@ -2,17 +2,19 @@ package validate
 
 import (
 	"errors"
-	"fmt"
+)
+
+// Validation error.
+var (
+	ErrTooFewChars  = errors.New("too few characters")
+	ErrTooManyChars = errors.New("too many characters")
 )
 
 // MaxLength validates the length of a string as being less than or equal to a given maximum.
 func MaxLength(l int) func(string) error {
 	return func(value string) error {
 		if len(value) > l {
-			if l != 1 {
-				return fmt.Errorf("Must not be longer than %d characters", l)
-			}
-			return errors.New("Must not be longer than 1 character")
+			return ErrTooManyChars
 		}
 		return nil
 	}
@@ -22,10 +24,7 @@ func MaxLength(l int) func(string) error {
 func MinLength(l int) func(string) error {
 	return func(value string) error {
 		if len(value) < l {
-			if l != 1 {
-				return fmt.Errorf("Must not be shorter than %d characters", l)
-			}
-			return errors.New("Must not be shorter than 1 character")
+			return ErrTooFewChars
 		}
 		return nil
 	}