support for ghc 8.6

in the MonadFail proposal's transitional strategy
  (https://wiki.haskell.org/MonadFail_Proposal#Transitional_strategy),
they explain that in ghc 8.6, -XMonadFailDesugaring becomes on by
default, which means that failed pattern-matching in a do block now
desugars to "MonadFail.fail" instead of "Monad.fail". Thus, for
consistency, our explicit calls to the "fail" function should also call
"MonadFail.fail" instead of "Monad.fail".

haskell-awk.cabal

@@ -1,8 +1,10 @@
 cabal-version: 1.24
 
--- This file has been generated from package.yaml by hpack version 0.34.2.
+-- This file has been generated from package.yaml by hpack version 0.33.0.
 --
 -- see: https://github.com/sol/hpack
+--
+-- hash: 7dd381c447e05d6cb34cf285e92876a4733dfdf88c0f8caf7e5a6b5945fca4fd
 
 name:           haskell-awk
 version:        1.2
@@ -47,7 +49,7 @@ library
       base >=4.9 && <5
     , bytestring >=0.10.6
     , containers >=0.5.7
-    , ghc (>8.0 && <8.5) || >8.8
+    , ghc >8.0
     , list-t >=0.4
     , stringsearch >=0.3.6.6
   if os(windows)
@@ -104,7 +106,7 @@ executable hawk
     , extra >=1.4
     , filelock >=0.1
     , filepath >=1.4
-    , ghc (>8.0 && <8.5) || >8.8
+    , ghc >8.0
     , haskell-awk
     , haskell-src-exts >=1.18
     , hint >=0.4
@@ -182,7 +184,7 @@ test-suite reference
     , extra >=1.5
     , filelock >=0.1
     , filepath >=1.4.1
-    , ghc (>8.0 && <8.5) || >8.8
+    , ghc >8.0
     , haskell-awk
     , haskell-src-exts >=1.18
     , hint >=0.6

package.yaml

@@ -20,7 +20,7 @@ dependencies:
   - base >= 4.9 && < 5
   - bytestring >= 0.10.6
   - containers >= 0.5.7
-  - ghc (> 8.0 && < 8.5) || > 8.8
+  - ghc > 8.0
   - list-t >= 0.4
 
 # Windows is not currently supported, see issue #248

src/Control/Monad/Trans/OptionParser.hs

@@ -3,11 +3,15 @@
 --   designed to look as if the options had more precise types than String.
 module Control.Monad.Trans.OptionParser where
 
-import Control.Monad
-#if MIN_VERSION_base(4,13,0)
-import qualified Control.Monad.Fail as Fail
+import Prelude hiding (fail)
+
+import Control.Monad hiding (fail)
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (MonadFail, fail)
+#else
+import Prelude (MonadFail, fail)
 #endif
-import "mtl" Control.Monad.Identity
+import "mtl" Control.Monad.Identity hiding (fail)
 import "mtl" Control.Monad.Trans
 import Control.Monad.Trans.State
 import Data.List
@@ -76,9 +80,9 @@ instance Monad m => Monad (OptionParserT o m) where
   OptionParserT mx >>= f = OptionParserT (mx >>= f')
     where
       f' = unOptionParserT . f
-#if MIN_VERSION_base(4,13,0)
+#if MIN_VERSION_base(4,12,0)
 
-instance Monad m => Fail.MonadFail (OptionParserT o m) where
+instance Monad m => MonadFail (OptionParserT o m) where
 #endif
   fail s = OptionParserT (fail s)
 
@@ -370,7 +374,7 @@ filePath = Setting "path"
 -- | The value assigned to the option if the check function doesn't fail with
 -- an error. The check functions must return a file path.
 --
--- >>> import Control.Monad
+-- >>> import Control.Monad hiding (fail)
 -- >>> import System.EasyFile (doesDirectoryExist)
 -- >>> let testIO args tp p = runUncertainIO $ runOptionParserWith head id (const [""]) tp ["input-dir"] p args
 -- >>> let inputDir = const filePath

src/Control/Monad/Trans/State/Persistent.hs

@@ -4,6 +4,9 @@ module Control.Monad.Trans.State.Persistent where
 
 import Control.Applicative
 import Control.Monad
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (MonadFail)
+#endif
 import Control.Monad.IO.Class
 import "mtl" Control.Monad.Trans
 import Control.Monad.Trans.Maybe
@@ -68,7 +71,7 @@ withPersistentState f default_s sx = do
 --
 -- >>> removeFile f
 withPersistentStateT :: forall m s a. (Functor m, MonadIO m,
-#if MIN_VERSION_base(4,13,0)
+#if MIN_VERSION_base(4,12,0)
                                        MonadFail m,
 #endif
                                        Read s, Show s, Eq s)

src/Control/Monad/Trans/Uncertain.hs

@@ -2,11 +2,15 @@
 -- | A computation which may raise warnings or fail in error.
 module Control.Monad.Trans.Uncertain where
 
-#if MIN_VERSION_base(4,13,0)
-import qualified Control.Monad.Fail as Fail
+import Prelude hiding (fail)
+
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (MonadFail, fail)
+#else
+import Prelude (MonadFail, fail)
 #endif
 import "mtl" Control.Monad.Trans
-import "mtl" Control.Monad.Identity
+import "mtl" Control.Monad.Identity hiding (fail)
 import "transformers" Control.Monad.Trans.Except
 import "transformers" Control.Monad.Trans.Writer
 import System.Exit
@@ -34,9 +38,9 @@ instance Monad m => Monad (UncertainT m) where
   UncertainT mx >>= f = UncertainT (mx >>= f')
     where
       f' = unUncertainT . f
-#if MIN_VERSION_base(4,13,0)
+#if MIN_VERSION_base(4,12,0)
 
-instance Monad m => Fail.MonadFail (UncertainT m) where
+instance Monad m => MonadFail (UncertainT m) where
 #endif
   fail s = UncertainT (throwE s)
 

src/Data/HaskellModule/Parse.hs

@@ -1,7 +1,14 @@
-{-# LANGUAGE OverloadedStrings, PackageImports, RecordWildCards, ScopedTypeVariables #-}
+{-# LANGUAGE CPP, OverloadedStrings, PackageImports, RecordWildCards, ScopedTypeVariables #-}
 -- | In which a Haskell module is deconstructed into extensions and imports.
 module Data.HaskellModule.Parse (readModule) where
 
+import Prelude hiding (fail)
+
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (fail)
+#else
+import Prelude (fail)
+#endif
 import "mtl" Control.Monad.Trans
 import qualified Data.ByteString.Char8 as B
 import Data.List

src/Data/HaskellSource.hs

@@ -1,9 +1,17 @@
+{-# LANGUAGE CPP #-}
 -- | A representation of Haskell source code.
 -- 
 -- Unlike haskell-src-exts, our goal is not to reconstruct detailed semantics,
 -- but to preserve original line numbers (if applicable).
 module Data.HaskellSource where
 
+import Prelude hiding (fail)
+
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (fail)
+#else
+import Prelude (fail)
+#endif
 import Control.Monad.Trans.Class
 import Data.ByteString.Char8 as B
 import System.Directory

src/System/Console/Hawk.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 --   Copyright 2013 Mario Pastorelli (pastorelli.mario@gmail.com) Samuel Gélineau (gelisam@gmail.com)
 --
 --   Licensed under the Apache License, Version 2.0 (the "License");
@@ -18,7 +19,13 @@ module System.Console.Hawk
   ( processArgs
   ) where
 
+import Prelude hiding (fail)
 
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (fail)
+#else
+import Prelude (fail)
+#endif
 import Control.Monad.Trans
 import Data.List
 import Language.Haskell.Interpreter

src/System/Console/Hawk/Args/Parse.hs

@@ -1,7 +1,14 @@
-{-# LANGUAGE OverloadedStrings, PackageImports, ScopedTypeVariables #-}
+{-# LANGUAGE CPP, OverloadedStrings, PackageImports, ScopedTypeVariables #-}
 -- | In which Hawk's command-line arguments are structured into a `HawkSpec`.
 module System.Console.Hawk.Args.Parse (parseArgs) where
 
+import Prelude hiding (fail)
+
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (fail)
+#else
+import Prelude (fail)
+#endif
 import Data.Char                                 (isSpace)
 import Data.Maybe
 import "mtl" Control.Monad.Trans

src/System/Console/Hawk/Context/Dir.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE PackageImports #-}
+{-# LANGUAGE CPP, PackageImports #-}
 -- | About the directory in which the context is persited.
 module System.Console.Hawk.Context.Dir
   ( createDefaultContextDir
@@ -6,7 +6,14 @@ module System.Console.Hawk.Context.Dir
   , checkContextDir
   ) where
 
-import Control.Monad
+import Prelude hiding (fail)
+
+import Control.Monad hiding (fail)
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (fail)
+#else
+import Prelude (fail)
+#endif
 import "mtl" Control.Monad.Trans
 import System.Directory
 import System.FilePath

src/System/Console/Hawk/Interpreter.hs

@@ -1,10 +1,18 @@
+{-# LANGUAGE CPP #-}
 -- | A wrapper around the hint library, specialized for Hawk usage.
 module System.Console.Hawk.Interpreter
   ( applyContext
   , runHawkInterpreter
   ) where
 
-import Control.Monad
+import Prelude hiding (fail)
+
+import Control.Monad hiding (fail)
+#if MIN_VERSION_base(4,12,0)
+import Control.Monad.Fail (fail)
+#else
+import Prelude (fail)
+#endif
 import Data.List
 import Language.Haskell.Interpreter
 

src/System/Console/Hawk/UserExpr/CanonicalExpr.hs

@@ -1,6 +1,6 @@
+{-# LANGUAGE CPP #-}
 module System.Console.Hawk.UserExpr.CanonicalExpr where
 
-
 import qualified Data.ByteString.Lazy.Char8 as B
 
 import Data.HaskellExpr