Text.Pandoc.Shared: remove findM [API change].

This was only used in one place, and can be replaced with simpler
code.

src/Text/Pandoc/App/Opt.hs

@@ -43,7 +43,6 @@ import Text.Pandoc.Options (TopLevelDivision (TopLevelDefault),
 import Text.Pandoc.Class (readFileStrict, fileExists, setVerbosity, report,
                           PandocMonad(lookupEnv), getUserDataDir)
 import Text.Pandoc.Error (PandocError (PandocParseError, PandocSomeError))
-import Text.Pandoc.Shared (findM)
 import Data.Containers.ListUtils (nubOrd)
 import Text.Pandoc.Data (defaultUserDataDir)
 import qualified Text.Pandoc.Parsing as P
@@ -802,7 +801,14 @@ fullDefaultsPath dataDir file = do
               else file
   defaultDataDir <- liftIO defaultUserDataDir
   let defaultFp = fromMaybe defaultDataDir dataDir </> "defaults" </> fp
-  fromMaybe fp <$> findM fileExists [fp, defaultFp]
+  fpExists <- fileExists fp
+  if fpExists
+     then return fp
+     else do
+       defaultFpExists <- fileExists defaultFp
+       if defaultFpExists
+          then return defaultFp
+          else return fp
 
 -- | In a list of lists, append another list in front of every list which
 -- starts with specific element.

src/Text/Pandoc/Shared.hs

@@ -22,7 +22,6 @@ module Text.Pandoc.Shared (
                      splitBy,
                      splitTextBy,
                      splitTextByIndices,
-                     findM,
                      -- * Text processing
                      inquotes,
                      tshow,
@@ -153,18 +152,6 @@ splitAt' n xs | n <= 0 = ([],xs)
 splitAt' n (x:xs)      = (x:ys,zs)
   where (ys,zs) = splitAt' (n - charWidth x) xs
 
--- | Returns the first element in a foldable structure for that the
--- monadic predicate holds true, and @Nothing@ if no such element
--- exists.
-findM :: forall m t a. (Monad m, Foldable t)
-      => (a -> m Bool) -> t a -> m (Maybe a)
-findM p = foldr go (pure Nothing)
-  where
-    go :: a -> m (Maybe a) -> m (Maybe a)
-    go x acc = do
-      b <- p x
-      if b then pure (Just x) else acc
-
 --
 -- Text processing
 --