From e3d8d57fc1a2c0e9f48605c4cd943d10eb6f27b9 Mon Sep 17 00:00:00 2001
From: Oleg Grenrus <oleg.grenrus@iki.fi>
Date: Fri, 19 Nov 2021 12:02:37 +0200
Subject: [PATCH 1/3] Add reproducer for issue 127

---
 parsec.cabal     |  7 +++++++
 test/issue127.hs | 13 +++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 test/issue127.hs

diff --git a/parsec.cabal b/parsec.cabal
index d549068..ef5deec 100644
--- a/parsec.cabal
+++ b/parsec.cabal
@@ -128,3 +128,10 @@ test-suite parsec.
         ghc-options: -Wcompat -Wnoncanonical-monad-instances -Wnoncanonical-monadfail-instances
     else
         build-depends: semigroups
+
+test-suite parsec-issue127
+    default-language: Haskell2010
+    type: exitcode-stdio-1.0
+    main-is: issue127.hs
+    hs-source-dirs: test
+    build-depends: base, parsec
diff --git a/test/issue127.hs b/test/issue127.hs
new file mode 100644
index 0000000..2ce827b
--- /dev/null
+++ b/test/issue127.hs
@@ -0,0 +1,13 @@
+module Main (main) where
+  
+import Text.Parsec
+import System.Environment (getArgs)
+import Control.Monad (replicateM_)
+
+main :: IO ()
+main = do
+  n <- getArgs >>= \args -> return $ case args of
+      arg : _ -> read arg
+      _       -> 1000000
+
+  print $ runParser (replicateM_ n $ return ()) () "test" ""

From b00129b5c18be6b2ffba3519761d90bc7ad0764c Mon Sep 17 00:00:00 2001
From: Zubin Duggal <zubin@cmi.ac.in>
Date: Mon, 22 Mar 2021 16:14:32 +0530
Subject: [PATCH 2/3] plug leak in bind

---
 src/Text/Parsec/Prim.hs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/Text/Parsec/Prim.hs b/src/Text/Parsec/Prim.hs
index 1dfd7bd..9da4b48 100644
--- a/src/Text/Parsec/Prim.hs
+++ b/src/Text/Parsec/Prim.hs
@@ -318,7 +318,9 @@ parserBind m k
   = ParsecT $ \s cok cerr eok eerr ->
     let
         -- consumed-okay case for m
-        mcok x s err =
+        mcok x s err
+          | errorIsUnknown err = unParser (k x) s cok cerr cok cerr
+          | otherwise =
             let
                  -- if (k x) consumes, those go straigt up
                  pcok = cok
@@ -335,7 +337,9 @@ parserBind m k
             in  unParser (k x) s pcok pcerr peok peerr
 
         -- empty-ok case for m
-        meok x s err =
+        meok x s err
+          | errorIsUnknown err = unParser (k x) s cok cerr eok eerr
+          | otherwise =
             let
                 -- in these cases, (k x) can return as empty
                 pcok = cok

From a07385ae6caf037196787dffa81a3bf701655f7f Mon Sep 17 00:00:00 2001
From: Oleg Grenrus <oleg.grenrus@iki.fi>
Date: Fri, 19 Nov 2021 12:04:08 +0200
Subject: [PATCH 3/3] Add changelog entry

---
 ChangeLog.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ChangeLog.md b/ChangeLog.md
index 58e6980..690c717 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -2,6 +2,7 @@
 
 - Add `INLINABLE` pragmas to most overloaded combinators
 - Support recent versions of dependencies
+- Fix memory leak in `>>=` https://github.com/haskell/parsec/issues/127
 
 ### 3.1.14.0