From fe5fd12812e657c720cc2c2ddff314ad7c1547fd Mon Sep 17 00:00:00 2001
From: Alexander Krotov <ilabdsf@gmail.com>
Date: Mon, 5 Feb 2018 15:41:51 +0300
Subject: Muse reader: avoid reparsing at the top level

Blocks following paragraphs are parsed only once at the top level.
Lists still take exponential time to parse, but this time is not
doubled anymore when this list terminates paragraph.
---
 src/Text/Pandoc/Readers/Muse.hs | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

(limited to 'src')

diff --git a/src/Text/Pandoc/Readers/Muse.hs b/src/Text/Pandoc/Readers/Muse.hs
index d985f5cf8..f24ad9274 100644
--- a/src/Text/Pandoc/Readers/Muse.hs
+++ b/src/Text/Pandoc/Readers/Muse.hs
@@ -130,8 +130,7 @@ instance HasLogMessages MuseState where
 parseMuse :: PandocMonad m => MuseParser m Pandoc
 parseMuse = do
   many directive
-  blocks <- mconcat <$> many parseBlock
-  eof
+  blocks <- parseBlocks
   st <- getState
   let doc = runF (do Pandoc _ bs <- B.doc <$> blocks
                      meta <- museMeta st
@@ -250,6 +249,19 @@ directive = do
 -- block parsers
 --
 
+parseBlocks :: PandocMonad m
+            => MuseParser m (F Blocks)
+parseBlocks =
+  try (mempty <$ eof) <|>
+  try blockStart <|>
+  try paraStart
+  where
+    blockStart = do first <- blockElements
+                    rest <- parseBlocks
+                    return $ first B.<> rest
+    paraStart = do (first, rest) <- paraUntil ((mempty <$ eof) <|> (blankline >> blockStart))
+                   return $ first B.<> rest
+
 parseBlock :: PandocMonad m => MuseParser m (F Blocks)
 parseBlock = do
   res <- blockElements <|> para
-- 
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