以下代码来自yesod-simple scaffold创建的Home.hs文件。 我喜欢在文本输入上进行简单的字符串操作,但不知道如何将其解析为Text值。 例如,我如何在fileDescription上使用toUpper? 我尝试过使用lookupPostParam 但我正在努力使用它的类型签名:
module Handler.Home where
import Import
import Yesod.Form.Bootstrap3 (BootstrapFormLayout (..), renderBootstrap3)
import Text.Julius (RawJS (..))
data FileForm = FileForm
{ fileInfo :: FileInfo
, fileDescription :: Text
}
getHomeR :: Handler Html
getHomeR = do
(formWidget, formEnctype) <- generateFormPost sampleForm
let submission = Nothing :: Maybe FileForm
handlerName = "getHomeR" :: Text
defaultLayout $ do
let (commentFormId, commentTextareaId, commentListId) = commentIds
aDomId <- newIdent
setTitle "Welcome To Yesod!"
$(widgetFile "homepage")
postHomeR :: Handler Html
postHomeR = do
((result, formWidget), formEnctype) <- runFormPost sampleForm
let handlerName = "postHomeR" :: Text
submission = case result of
FormSuccess res -> Just res
_ -> Nothing
defaultLayout $ do
let (commentFormId, commentTextareaId, commentListId) = commentIds
aDomId <- newIdent
setTitle "Welcome To Yesod!"
$(widgetFile "homepage")
sampleForm :: Form FileForm
sampleForm = renderBootstrap3 BootstrapBasicForm $ FileForm
<$> fileAFormReq "Choose a file"
<*> areq textField textSettings Nothing
where textSettings = FieldSettings
{ fsLabel = "What's on the file?"
, fsTooltip = Nothing
, fsId = Nothing
, fsName = Nothing
, fsAttrs =
[ ("class", "form-control")
, ("placeholder", "File description")
]
}
commentIds :: (Text, Text, Text)
commentIds = ("js-commentForm", "js-createCommentTextarea", "js-
commentList")
Home.hs
import { Directive, Input, HostListener } from '@angular/core';
@Directive({
selector: '[limitTo]'
})
export class LimitToDirective {
@Input() limit: number;
constructor() {
}
@HostListener("keypress", ["$event"])
onkeypress(event) {
if (event.target.value.length === this.limit) {
event.preventDefault();
}
}
}
答案 0 :(得分:1)
遗憾的是,这是文档和沟通方面的错误。
鉴于
lookupPostParam :: (MonadResource m, MonadHandler m) => Text -> m (Maybe Text)
读者可以推断m
不仅是MonadResouce
和MonadHandler
,还有Monad
。这一小段代码将很多意图包含在一个非常小的句子中; Haskell库的大量使用是隐含的和潜在的,这是一个疣。例如,要在此类型的toUpper
内调用Text
,您就是这样做的:
{-# language OverloadedStrings #-}
foo :: (MonadResource m, MonadHandler m) => m (Maybe Text)
foo = do
valueMaybe <- lookupPostParam "key"
case valueMaybe of
Just value ->
pure (toUpper value)
Nothing ->
Nothing
请注意,monad堆栈(MonadHandler
,MonadResource
)已“感染”了您的代码。这是故意的,以便通过类型检查器限制您只在预期的Yesod环境/状态机/上下文/中运行此函数。
您使用的是yesod-forms,在该框架内执行相同的操作会很不错。与lookupPostParam
一样,我们可以利用monad-applicative-functor类型类。
我们可以根据您的Form FileForm
值进行调整。
sampleForm :: AForm Handler FileForm
sampleForm =
FileForm <$> fileAFormReq "Choose a file"
<*> (toUpper <$> areq textField textSettings Nothing)
我认为版本之间yesod-forms
的类型发生了变化。我在写作时将我的类型从最新版本复制到1.4.11。
这里我们利用Monad m => Functor (AForm m)
实例。知道我们确实在monad(Handler
monad)中意味着我们可以使用fmap
及其不相关的兄弟<$>
来areq textField textSettings Nothing
返回的值。这允许我们将Text
上的任意函数提升到AForm m
堆栈中。例如,我们从Text -> Text
转到AForm Handler Text -> AForm Handler Text
。
希望有所帮助。