From cc543cf5b64cccc91ad6a1a455831b8c3f6d80b2 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Sun, 28 Feb 2021 14:34:04 -0800
Subject: LaTeX reader: another small efficiency improvement.

---
 src/Text/Pandoc/Readers/LaTeX.hs | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

(limited to 'src/Text')

diff --git a/src/Text/Pandoc/Readers/LaTeX.hs b/src/Text/Pandoc/Readers/LaTeX.hs
index 4956b90cb..4062e8a53 100644
--- a/src/Text/Pandoc/Readers/LaTeX.hs
+++ b/src/Text/Pandoc/Readers/LaTeX.hs
@@ -1855,12 +1855,18 @@ orderedList' = try $ do
 
 block :: PandocMonad m => LP m Blocks
 block = do
-  res <- (mempty <$ spaces1)
-    <|> environment
-    <|> macroDef (rawBlock "latex")
-    <|> blockCommand
-    <|> paragraph
-    <|> grouped block
+  Tok _ toktype _ <- lookAhead anyTok
+  res <- (case toktype of
+            Newline           -> mempty <$ spaces1
+            Spaces            -> mempty <$ spaces1
+            Comment           -> mempty <$ spaces1
+            Word              -> paragraph
+            CtrlSeq "begin"   -> environment
+            CtrlSeq _         -> macroDef (rawBlock "latex")
+                               <|> blockCommand
+            _                 -> mzero)
+          <|> paragraph
+          <|> grouped block
   trace (T.take 60 $ tshow $ B.toList res)
   return res
 
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