From c0c8865eaac7089b0304c9b21d981f82ea4c2ebd Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Sat, 20 Feb 2021 23:40:02 -0800
Subject: HTML reader: small performance tweak.

---
 src/Text/Pandoc/Readers/HTML.hs | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/src/Text/Pandoc/Readers/HTML.hs b/src/Text/Pandoc/Readers/HTML.hs
index 50201fe77..b73c138ab 100644
--- a/src/Text/Pandoc/Readers/HTML.hs
+++ b/src/Text/Pandoc/Readers/HTML.hs
@@ -157,11 +157,10 @@ pHead = pInTags "head" $ pTitle <|> pMetaTag <|> pBaseTag <|> (mempty <$ pAny)
           return mempty
 
 block :: PandocMonad m => TagParser m Blocks
-block = do
+block = ((do
+  tag <- lookAhead (pSatisfy isBlockTag)
   exts <- getOption readerExtensions
-  tag <- lookAhead pAny
-  res <-
-   (case tag of
+  case tag of
     TagOpen name attr ->
       let type' = fromMaybe "" $
                      lookup "type" attr <|> lookup "epub:type" attr
@@ -214,11 +213,8 @@ block = do
           | epubExts
           -> eSwitch B.para block
         _ -> mzero
-    _ -> mzero)
-   <|> pPlain
-   <|> pRawHtmlBlock
-  trace (T.take 60 $ tshow $ B.toList res)
-  return res
+    _ -> mzero) <|> pPlain <|> pRawHtmlBlock) >>= \res ->
+        res <$ trace (T.take 60 $ tshow $ B.toList res)
 
 namespaces :: PandocMonad m => [(Text, TagParser m Inlines)]
 namespaces = [(mathMLNamespace, pMath True)]
-- 
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