From 7fa5fbed9e0440694e9c52a8dc83f3e4f29c8a96 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Thu, 28 Mar 2019 13:51:15 -0700
Subject: Use strict instead of lazy sum.

sum is lazy; replace with `foldl' (+) 0` to avoid stack
overflow in Text.Pandoc.Pretty with very long strings.

Closes #5401.
---
 src/Text/Pandoc/Pretty.hs         | 6 +++---
 src/Text/Pandoc/Writers/Shared.hs | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/Text/Pandoc/Pretty.hs b/src/Text/Pandoc/Pretty.hs
index 2d7a3a725..ad223274e 100644
--- a/src/Text/Pandoc/Pretty.hs
+++ b/src/Text/Pandoc/Pretty.hs
@@ -65,7 +65,7 @@ import Control.Monad
 import Control.Monad.State.Strict
 import Data.Char (isSpace)
 import Data.Foldable (toList)
-import Data.List (intersperse)
+import Data.List (intersperse, foldl')
 import Data.Sequence (Seq, ViewL (..), fromList, mapWithIndex, singleton, viewl,
                       (<|))
 import qualified Data.Sequence as Seq
@@ -305,7 +305,7 @@ renderList (BreakingSpace : xs) = do
   let xs' = dropWhile isBreakingSpace xs
   let next = takeWhile isText xs'
   st <- get
-  let off = sum $ map offsetOf next
+  let off = foldl' (+) 0 $ map offsetOf next
   case lineLength st of
         Just l | column st + 1 + off > l -> do
           outp (-1) "\n"
@@ -540,4 +540,4 @@ charWidth c =
 -- | Get real length of string, taking into account combining and double-wide
 -- characters.
 realLength :: String -> Int
-realLength = sum . map charWidth
+realLength = foldl' (+) 0 . map charWidth
diff --git a/src/Text/Pandoc/Writers/Shared.hs b/src/Text/Pandoc/Writers/Shared.hs
index 7027a9576..f4370b7bf 100644
--- a/src/Text/Pandoc/Writers/Shared.hs
+++ b/src/Text/Pandoc/Writers/Shared.hs
@@ -41,7 +41,7 @@ import Data.Aeson (FromJSON (..), Result (..), ToJSON (..), Value (Object),
                    encode, fromJSON)
 import Data.Char (chr, ord, isSpace, isDigit)
 import qualified Data.HashMap.Strict as H
-import Data.List (groupBy, intersperse, transpose)
+import Data.List (groupBy, intersperse, transpose, foldl')
 import qualified Data.Map as M
 import Data.Maybe (isJust)
 import qualified Data.Text as T
@@ -279,7 +279,7 @@ gridTable opts blocksToDoc headless aligns widths headers rows = do
   -- handleGivenWidths
   let handleZeroWidths = do
         (widthsInChars', rawHeaders', rawRows') <- handleFullWidths
-        if sum widthsInChars' > writerColumns opts
+        if foldl' (+) 0 widthsInChars' > writerColumns opts
            then -- use even widths
                 handleGivenWidths
                   (replicate numcols (1.0 / fromIntegral numcols) :: [Double])
-- 
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