Invert module-dep between Control.Monad and Data.Foldable

This is the last preparation needed before generalizing entities in
Control.Monad conflicting with those from Data.Foldable (re #9586)

Reviewed By: ekmett, austin

Differential Revision: https://phabricator.haskell.org/D225

2 files changed, 11 insertions, 2 deletions

diff --git a/libraries/base/Text/ParserCombinators/ReadP.hs b/libraries/base/Text/ParserCombinators/ReadP.hs
index 3d2b39c57e..0139e7733d 100644
--- a/libraries/base/Text/ParserCombinators/ReadP.hs
+++ b/libraries/base/Text/ParserCombinators/ReadP.hs
@@ -72,7 +72,6 @@ module Text.ParserCombinators.ReadP
   )
  where
 
-import Control.Monad ( sequence )
 import {-# SOURCE #-} GHC.Unicode ( isSpace )
 import GHC.List ( replicate, null )
 import GHC.Base hiding ( many )
@@ -311,6 +310,10 @@ count :: Int -> ReadP a -> ReadP [a]
 -- ^ @count n p@ parses @n@ occurrences of @p@ in sequence. A list of
 --   results is returned.
 count n p = sequence (replicate n p)
+  where -- local 'sequence' to avoid import-cycle
+    sequence ms = foldr k (return []) ms
+      where
+        k m m' = do { x <- m; xs <- m'; return (x:xs) }
 
 between :: ReadP open -> ReadP close -> ReadP a -> ReadP a
 -- ^ @between open close p@ parses @open@, followed by @p@ and finally
diff --git a/libraries/base/Text/Read/Lex.hs b/libraries/base/Text/Read/Lex.hs
index 557637d896..39ca46a33f 100644
--- a/libraries/base/Text/Read/Lex.hs
+++ b/libraries/base/Text/Read/Lex.hs
@@ -45,7 +45,13 @@ import GHC.Real( Rational, (%), fromIntegral,
 import GHC.List
 import GHC.Enum( minBound, maxBound )
 import Data.Maybe
-import Control.Monad
+
+-- local copy to break import-cycle
+-- | @'guard' b@ is @'return' ()@ if @b@ is 'True',
+-- and 'mzero' if @b@ is 'False'.
+guard           :: (MonadPlus m) => Bool -> m ()
+guard True      =  return ()
+guard False     =  mzero
 
 -- -----------------------------------------------------------------------------
 -- Lexing types