purescript - 我如何才能将 Maybe 转换为 Value？

Question

我的代码有问题 我正在尝试编译它，但它抛出无法匹配 Maybe Element 与 Element

为什么？ Maybe 如何工作？如何将其转换为值？为什么 monads 和 functor 这么难理解，为什么没有一个简单的库可以让一些新手开始使用纯脚本？:P

(对于那些不明白的人我只问了前3个)

module Main where

import Prelude --(Unit, bind, pure,  ($), (<$>))
import Effect (Effect)
import Data.Maybe --(Just,Maybe,fromJust, fromMaybe)
import Data.Foldable (traverse_)
import Effect.Console (log)

import Web.HTML (window)
import Web.HTML.Window (document)
import Web.HTML.HTMLDocument (toNonElementParentNode)
import Web.Event.Event (Event, target)
import Web.HTML.HTMLInputElement (value, fromEventTarget)

import Web.DOM.NonElementParentNode (NonElementParentNode,getElementById)
import Web.DOM.Node (setTextContent)
import Web.DOM.Element (Element,toNode)
import Web.Event.EventTarget (addEventListener)

pname = "#inputName" :: String
bname = "#badgeName" :: String

main :: Effect Unit
main = do
  nod1 <- returnNonElementParentNode
--querySelector :: QuerySelector -> ParentNode -> Effect (Maybe Element)
  elementTarget <- getElementById pname nod1
--addEventListener :: EventType -> EventListener -> Boolean -> EventTarget
  addEventListener "input" updateBadge false elementTarget

updateBadge :: Event -> Unit
updateBadge event = do
  nod2 <- returnNonElementParentNode
  elementTarget <- getElementById bname nod2

  tget <- target event
  inml <- fromEventTarget tget
  input <- value inml

  badge <- toNode (pure elementTarget)

  if not(badge == Nothing) 
    then setTextContent input (toNode badge) 
    else Nothing

returnNonElementParentNode :: Effect NonElementParentNode
returnNonElementParentNode = do 
  win <- window
  doc <- document win
  --let nd  = toNonElementParentNode doc
  let 
      nod = toNonElementParentNode doc
  pure nod

我只想了解如何从 htmlInputElement 获取输入值并将其传递给另一个 HTMLElement 的 textContent

关于如何将 Maybe 转换为 Value 以传递给 toNode 函数

Answer 1

• 模式匹配... https://github.com/purescript/documentation/blob/master/language/Pattern-Matching.md
• Data.Maybe#v:也许... https://pursuit.purescript.org/packages/purescript-maybe/4.0.1/docs/Data.Maybe#v:maybe
• Data.Maybe#v:fromMaybe ... https://pursuit.purescript.org/packages/purescript-maybe/4.0.1/docs/Data.Maybe#v:fromMaybe
• Partial.Unsafe#v:unsafePartial + Data.Maybe#v:fromJust https://pursuit.purescript.org/packages/purescript-partial/2.0.1/docs/Partial.Unsafe#v:unsafePartial https://pursuit.purescript.org/packages/purescript-maybe/4.0.1/docs/Data.Maybe#v:fromJust