new errors

internal/executor/add.go

@@ -265,11 +265,11 @@ func (a *AddExecutor) addVoteToPoll(gtsClient *client.Client) error {
 	}
 
 	if poll.Expired {
-		return errors.New("this poll has expired")
+		return ExpiredPollError{}
 	}
 
 	if !poll.Multiple && len(a.choices) > 1 {
-		return errors.New("this poll does not allow multiple choices")
+		return MultipleChoiceError{}
 	}
 
 	if err := gtsClient.VoteInPoll(a.pollID, []int(a.choices)); err != nil {

internal/executor/errors.go

@@ -66,3 +66,15 @@ type UnknownCommandError struct {
 func (e UnknownCommandError) Error() string {
 	return "unknown command '" + e.Command + "'"
 }
+
+type ExpiredPollError struct{}
+
+func (e ExpiredPollError) Error() string {
+	return "this poll has expired"
+}
+
+type MultipleChoiceError struct{}
+
+func (e MultipleChoiceError) Error() string {
+	return "this poll does not allow multiple choices"
+}