Copy readMaybe/readEither from base >= 4.7 for backwards compatibility

Language/Haskell/GhcMod/CabalConfig.hs

@@ -6,6 +6,7 @@ module Language.Haskell.GhcMod.CabalConfig (
 
 import Language.Haskell.GhcMod.GhcPkg
 import Language.Haskell.GhcMod.Utils
+import Language.Haskell.GhcMod.Read
 import Language.Haskell.GhcMod.Types
 
 import qualified Language.Haskell.GhcMod.Cabal16 as C16
@@ -24,7 +25,6 @@ import Distribution.Simple.BuildPaths (defaultDistPref)
 import Distribution.Simple.Configure (localBuildInfoFile)
 import Distribution.Simple.LocalBuildInfo (ComponentName)
 import System.FilePath ((</>))
-import Text.Read (readMaybe)
 ----------------------------------------------------------------
 
 type CabalConfig = String
@@ -94,7 +94,7 @@ configDependencies thisPkg config = map fromInstalledPackageId deps
          clbi <- stripPrefix " = " field
          if "Nothing" `isPrefixOf` clbi
              then Nothing
-             else case readMaybe <$> stripPrefix "Just " clbi of
+             else case readMaybe =<< stripPrefix "Just " clbi of
                     Just x -> x
                     Nothing -> error $ "reading libraryConfig failed\n" ++ show (stripPrefix "Just " clbi)
 
@@ -102,15 +102,9 @@ configDependencies thisPkg config = map fromInstalledPackageId deps
        extract field = readConfigs field <$> extractField config field
 
        readConfigs :: String -> String -> [(String, C16.ComponentLocalBuildInfo)]
-       readConfigs f s = case readMaybe s of
-           Just x -> x
-           Nothing -> error $ "reading config " ++ f ++ " failed"
-
-
-readEither :: Read r => String -> Either String r
-readEither s = case readMaybe s of
-    Just x -> Right x
-    Nothing -> Left $ "read: failed on input:\n" ++ s
+       readConfigs f s = case readEither s of
+           Right x -> x
+           Left msg -> error $ "reading config " ++ f ++ " failed ("++msg++")"
 
 extractField :: CabalConfig -> String -> Either String String
 extractField config field =

Language/Haskell/GhcMod/Read.hs

@@ -0,0 +1,106 @@
+module Language.Haskell.GhcMod.Read where
+
+import Text.Read (readPrec_to_S, readPrec, minPrec)
+import qualified Text.ParserCombinators.ReadP as P
+import Text.ParserCombinators.ReadPrec (lift)
+
+-- This library (libraries/base) is derived from code from several
+-- sources:
+
+--   * Code from the GHC project which is largely (c) The University of
+--     Glasgow, and distributable under a BSD-style license (see below),
+
+--   * Code from the Haskell 98 Report which is (c) Simon Peyton Jones
+--     and freely redistributable (but see the full license for
+--     restrictions).
+
+--   * Code from the Haskell Foreign Function Interface specification,
+--     which is (c) Manuel M. T. Chakravarty and freely redistributable
+--     (but see the full license for restrictions).
+
+-- The full text of these licenses is reproduced below.  All of the
+-- licenses are BSD-style or compatible.
+
+-- -----------------------------------------------------------------------------
+
+-- The Glasgow Haskell Compiler License
+
+-- Copyright 2004, The University Court of the University of Glasgow.
+-- All rights reserved.
+
+-- Redistribution and use in source and binary forms, with or without
+-- modification, are permitted provided that the following conditions are met:
+
+-- - Redistributions of source code must retain the above copyright notice,
+-- this list of conditions and the following disclaimer.
+
+-- - Redistributions in binary form must reproduce the above copyright notice,
+-- this list of conditions and the following disclaimer in the documentation
+-- and/or other materials provided with the distribution.
+
+-- - Neither name of the University nor the names of its contributors may be
+-- used to endorse or promote products derived from this software without
+-- specific prior written permission.
+
+-- THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY COURT OF THE UNIVERSITY OF
+-- GLASGOW AND THE CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+-- INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+-- FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+-- UNIVERSITY COURT OF THE UNIVERSITY OF GLASGOW OR THE CONTRIBUTORS BE LIABLE
+-- FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+-- DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+-- SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+-- CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+-- LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+-- OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+-- DAMAGE.
+
+-- -----------------------------------------------------------------------------
+
+-- Code derived from the document "Report on the Programming Language
+-- Haskell 98", is distributed under the following license:
+
+--   Copyright (c) 2002 Simon Peyton Jones
+
+--   The authors intend this Report to belong to the entire Haskell
+--   community, and so we grant permission to copy and distribute it for
+--   any purpose, provided that it is reproduced in its entirety,
+--   including this Notice.  Modified versions of this Report may also be
+--   copied and distributed for any purpose, provided that the modified
+--   version is clearly presented as such, and that it does not claim to
+--   be a definition of the Haskell 98 Language.
+
+-- -----------------------------------------------------------------------------
+
+-- Code derived from the document "The Haskell 98 Foreign Function
+-- Interface, An Addendum to the Haskell 98 Report" is distributed under
+-- the following license:
+
+--   Copyright (c) 2002 Manuel M. T. Chakravarty
+
+--   The authors intend this Report to belong to the entire Haskell
+--   community, and so we grant permission to copy and distribute it for
+--   any purpose, provided that it is reproduced in its entirety,
+--   including this Notice.  Modified versions of this Report may also be
+--   copied and distributed for any purpose, provided that the modified
+--   version is clearly presented as such, and that it does not claim to
+--   be a definition of the Haskell 98 Foreign Function Interface.
+
+-- -----------------------------------------------------------------------------
+
+readEither :: Read a => String -> Either String a
+readEither s =
+  case [ x | (x,"") <- readPrec_to_S read' minPrec s ] of
+    [x] -> Right x
+    []  -> Left "Prelude.read: no parse"
+    _   -> Left "Prelude.read: ambiguous parse"
+ where
+  read' =
+    do x <- readPrec
+       lift P.skipSpaces
+       return x
+
+readMaybe :: Read a => String -> Maybe a
+readMaybe s = case readEither s of
+                Left _  -> Nothing
+                Right a -> Just a

ghc-mod.cabal

@@ -79,6 +79,7 @@ Library
                         Language.Haskell.GhcMod.PkgDoc
                         Language.Haskell.GhcMod.Utils
                         Language.Haskell.GhcMod.Types
+                        Language.Haskell.GhcMod.Read
   Build-Depends:        base >= 4.0 && < 5
                       , containers
                       , deepseq