消化函子和 listOf

Question

我已经能够在 snap 应用程序中成功地使用带有简单表单的 digestive-functors；但是，我在尝试处理隐藏输入列表时遇到了困难。关于如何使用listOf，有些事情我不太了解。谁能指出我正确的方向？谢谢。

上一页呈现的 html 包含以下隐藏字段：

<div id='messageForm.recipients' class='inputList'>
  <input type='hidden' name='messageForm.recipients.indices' value='0' />
  <input type='hidden' id='messageForm.recipients.-1.email' name='messageForm.recipients.-1.email' value />
  <input type='hidden' id='messageForm.recipients.0.email' name='messageForm.recipients.0.email' value='emai1l@email.com' /> 
  <input type='hidden' id='messageForm.recipients.1.email' name='messageForm.recipients.1.email' value='email2@email.com' /> 
</div>

数据类型有：

data ConfirmMessage = ConfirmMessage {
  isoDate :: T.Text,
  subject :: T.Text,
  body    :: T.Text,
  action  :: T.Text,
  recipients :: [Recipient]
} deriving (Show) 

data Recipient = Recipient {
  email :: T.Text 
} deriving (Show)

表格有：

messageForm :: (Monad m) => Form T.Text m ConfirmMessage
messageForm = ConfirmMessage
  <$> "isoDate"    .: stringRead "Missing ISOdate" Nothing
  <*> "subject"    .: stringRead "Subject required" Nothing
  <*> "body"       .: stringRead "Body required" Nothing
  <*> "action"     .: stringRead "Missing action" Nothing
  <*> "recipients" .: listOf recipientForm' Nothing

recipientForm' :: (Monad m) => Formlet T.Text m Recipient
recipientForm'= Recipient
  <$> "email"      .: text Nothing

我得到的错误信息是：

Couldn't match type `Text.Digestive.Form.Internal.FormTree
                       m0 v0 m0 Recipient'
              with `Maybe Recipient -> Form T.Text m Recipient'
Expected type: Formlet T.Text m Recipient
  Actual type: Text.Digestive.Form.Internal.FormTree
                 m0 v0 m0 Recipient
Relevant bindings include
  recipientForm' :: Formlet T.Text m Recipient
    (bound at src/Handler/TradeNotifyConfirm.hs:191:1)
In the expression: Recipient <$> "email" .: text Nothing
In an equation for `recipientForm'':
    recipientForm' = Recipient <$> "email" .: text Nothing

Answer 1

好的免责声明：我从未使用过digestive-functors，但这是我处理此类问题的方法：

1) 您的错误消息显示Expected type: Formlet T.Text m Recipient 和Actual type: Text.Digestive.Form.Internal.FormTree m0 v0 m0 Recipient

2）查看文档并看到：

type Formlet v m a = Maybe a -> Form v m a 
type Form v m a = FormTree m v m a

所以我们从上面扩展预期得到：

Formlet T.Text m Recipient 
-- v ~ T.Text, a ~ Recipient
Maybe Recipient -> Form T.Text m Recipient
--
Maybe Recipient -> FormTree m T.Text m Recipient

现在再看一遍：

• 预期类型：Maybe Recipient -> FormTree m T.Text m Recipient
• 实际类型：FormTree m0 v0 m0 Recipient

我们缺少Maybe Recipient！根据我在上面看到的情况，我猜您只想忽略该论点，因此我们有：

recipientForm' :: (Monad m) => Formlet T.Text m Recipient
recipientForm' _ = Recipient <$> "email" .: text Nothing

编译得很好，耶:)