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HXT: Amazing behavior when reading and writing HTML in String in pure code

I want to read HTML from String, process it, and return the modified document as a string using HXT. Since this operation does not require I / O, I would rather runLA arrow with runLA than with runX .

The code looks like this (excluding processing for simplicity):

 runLA (hread >>> writeDocumentToString [withOutputHTML, withIndent yes]) html

However, the html tag is missing the result:

 ["\n <head>\n <title>Bogus</title>\n </head>\n <body>\n Some trivial bogus text.\n </body>\n",""]

When I use runX instead:

 runX (readString [] html >>> writeDocumentToString [withOutputHTML, withIndent yes])

I get the expected result:

 ["<html>\n <head>\n <title>Bogus</title>\n </head>\n <body>\n Some trivial bogus text.\n </body>\n</html>\n"]

Why is this and how can I fix it?

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1 answer

If you look at XmlTree for both, you will see that readString adds a top-level "/" element. For non- IO runLA :

 > putStr . formatTree show . head $ runLA xread html ---XTag "html" [] | +---XText "\n " | +---XTag "head" [] ...

And with runX :

 > putStr . formatTree show . head =<< runX (readString [] html) ---XTag "/" [NTree (XAttr "transfer-Status") [NTree (XText "200")... | +---XTag "html" [] | +---XText "\n " | +---XTag "head" [] ...

writeDocumentToString uses getChildren to remove this root element.

One easy way is to use something like selem to wrap the xread output in a similar root element so that it looks like the type of writeDocumentToString input:

 > runLA (selem "/" [xread] >>> writeDocumentToString [withOutputHTML, withIndent yes]) html ["<html>\n <head>\n <title>Bogus</title>\n </head>\n <body>\n Some trivial bogus text.\n </body>\n</html>\n"]

This gives the desired result.

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Source: https://habr.com/ru/post/1369211/

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