initial commits

errors/errors.go

@@ -10,6 +10,10 @@ const (
 	ErrUnexpectedEndOfFile = erorr.Error("rfc8259: unexpected end-of-file")
 )
 
+func ErrInternalError(msg string) error {
+	return erorr.Errorf("rfc8259: JSON parser had an unexpected internal-error — %s", msg)
+}
+
 func ErrProblemReadingRune(err error) error {
 	return erorr.Errorf("rfc8259: JSON parser had a problem — problem reading rune: %w", err)
 }

naturalnumber/parse_test.go

@@ -21,6 +21,10 @@ func TestParse_success(t *testing.T) {
 			Value: []byte("0"),
 			Expected: rfc8259naturalnumber.Zero(),
 		},
+		{
+			Value: []byte("-0"),
+			Expected: rfc8259naturalnumber.Something("-0"),
+		},