我一直承认自己镜头不好，但是通过实例学习不是一件好事吗？我想获取 HTML，使用 taggy-lens 解析它，然后从内部删除所有 script 元素。这是我的尝试:
#!/usr/bin/env stack
-- stack --resolver lts-7.1 --install-ghc runghc --package text --package lens --package taggy-lens --package string-class --package classy-prelude
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
import ClassyPrelude
import Control.Lens hiding (children, element)
import Data.String.Class (toText, fromText, toString)
import Data.Text (Text)
import Text.Taggy.Lens
import qualified Text.Taggy.Lens as Taggy
import qualified Text.Taggy.Renderer as Renderer
somehtmlSmall :: Text
somehtmlSmall =
"<!doctype html><html><body>\
\<div id=\"article\"><div>first</div><div>second</div><script>this should be removed</script><div>third</div></div>\
\</body></html>"
renderWithoutScriptTag :: Text
renderWithoutScriptTag =
let mArticle :: Maybe Taggy.Element
mArticle =
(fromText somehtmlSmall) ^? html .
allAttributed (ix "id" . only "article")
mArticleFiltered =
fmap
(\el ->
el ^.. to universe . traverse .
filtered (\n -> n ^. name /= "script"))
mArticle
in maybe "" (toText . concatMap Renderer.render) mArticleFiltered
main :: IO ()
main = print renderWithoutScriptTag
将此文件标记为可执行文件并运行它，您将看到:
➜ tmp ./scraping-question.hs
"<div id=\"article\"><div>first</div><div>second</div><script>this should be removed</script><div>third</div></div><div>first</div><div>second</div><div>third</div>"
所以，这不起作用。我愿意:
- 有可行的解决方案
- 了解可行的解决方案
如果您能帮助我意识到我的问题出在哪里，我会特别感激。谢谢!
最佳答案
问题的根源是universe，它将 DOM 树扁平化为一个列表。如果再次查看输出，您将看到过滤工作正常，但树结构丢失了——因此您得到未修改的article元素(所有子元素仍在其中)，后面跟着子节点减去script元素。
一个可以实现您想要的功能的 Control.Lens.Plated 组合器是 transform ，它以自下而上的方式转换“树中的每个元素”:
transform :: Plated a => (a -> a) -> a -> a
特别是，您可以使用它递归地过滤子节点:
renderWithoutScriptTag :: Text
renderWithoutScriptTag =
let mArticle :: Maybe Taggy.Element
mArticle =
(fromText somehtmlSmall) ^? html .
allAttributed (ix "id" . only "article")
mArticleFiltered =
fmap
(transform (children %~ filter (\n ->
n ^? element . name /= Just "script")))
mArticle
in maybe "" (toText . Renderer.render) mArticleFiltered
关于haskell - 通过镜头过滤树中的内部元素，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39786824/