嵌套形式导致 Haskell

Question

我有以下 handler/template 组合：

handler/automation.hs

data AutomationRequest = AutomationRequest {
    arEnabled :: Bool
  , arTemplate :: Text
  , arSchedules :: Textarea
}

getAutomationR :: Handler Html
getAutomationR = do
    (formWidget, formEnctype) <- generateFormPost form
    defaultLayout $(widgetFile "automation")

form :: Form AutomationRequest
form extra = do
    (enabledRes, enabledView) <- mreq checkBoxField "" Nothing
    (templateRes, templateView) <- mreq textField (withPlaceholder "..." $ bfs (""::Text)) Nothing
    (schedulesRes, schedulesView) <- mreq textareaField (withPlaceholder "..." $ bfs (""::Text)) Nothing
    (_, submitView) <- mbootstrapSubmit $ BootstrapSubmit ("Save"::Text) ("btn-primary"::Text) []
    let requestRes = AutomationRequest <$> enabledRes <*> templateRes <*> schedulesRes
        widget = $(widgetFile "automation-form")
    return (requestRes, widget)

templates/automation.hamlet

<form method=post role=form action=@{AutomationR} enctype=#{formEnctype}>
    ^{formWidget}

templates/automation-form.hamlet

#{extra}

<div .panel .panel-default>
    <div .panel-heading>^{fvInput enabledView} ...
    <div .panel-body>
        ^{fvInput templateView}
        ^{fvInput schedulesView}

^{fvInput submitView}

这按预期工作，但我需要额外的功能：

a) 我希望能够像这样嵌套数据结构：

data AutomationRequestCollection = AutomationRequestCollection {
    arcItemAbc :: AutomationRequest
  , arcItemDef :: AutomationRequest
  ... -- 10 Items

}

data AutomationRequest = AutomationRequest {
    arEnabled :: Bool
  , arTemplate :: Text
  , arSchedules :: Textarea
}

我不知道如何将嵌套应用到 let requestRes = AutomationRequest <$> enabledRes <*> templateRes <*> schedulesRes

b) 为 itemAbc、itemDef、...重复使用 HTML 面板：

-- loop somehow
<div .panel .panel-default>
    <div .panel-heading>^{fvInput enabledView} ...
    <div .panel-body>
        ^{fvInput templateView}
        ^{fvInput schedulesView}

有什么想法可以将我推向正确的方向吗？

Answer 1

我不确定(b)，但(a)应该是直截了当的应用组合，例如：

Foo <$> (Bar <$> baz <*> bin) <*> qux

如果把它分解成多个函数也能更容易看出来：

bar = Bar <$> baz <*> bin
foo = Foo <$> bar <*> qux

嵌套形式导致 Haskell

Nested form result in Haskell

haskell

yesod

applicative

yesod-forms