Merge pull request #38 from fabricatedmath/master

added 'embedFileIfExists'

Data/FileEmbed.hs

@@ -19,6 +19,7 @@
 module Data.FileEmbed
     ( -- * Embed at compile time
       embedFile
+    , embedFileIfExists
     , embedOneFileOf
     , embedDir
     , embedDirListing
@@ -60,13 +61,14 @@ import qualified Data.ByteString.Internal as B
 #endif
 import System.Directory (doesDirectoryExist, doesFileExist,
                          getDirectoryContents, canonicalizePath)
-import Control.Exception (throw, ErrorCall(..))
-import Control.Monad (filterM)
+import Control.Exception (throw, tryJust, ErrorCall(..))
+import Control.Monad (filterM, guard)
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Char8 as B8
 import Control.Arrow ((&&&), second)
 import Control.Applicative ((<$>))
 import Data.ByteString.Unsafe (unsafePackAddressLen)
+import System.IO.Error (isDoesNotExistError)
 import System.IO.Unsafe (unsafePerformIO)
 import System.FilePath ((</>), takeDirectory, takeExtension)
 import Data.String (fromString)
@@ -87,6 +89,31 @@ embedFile fp =
 #endif
   (runIO $ B.readFile fp) >>= bsToExp
 
+-- | Maybe embed a single file in your source code depending on whether or not file exists.
+--
+-- Warning: When a build is compiled with the file missing, a recompile when the file exists might not trigger an embed of the file.
+-- You might try to fix this by doing a clean build.
+--
+-- > import qualified Data.ByteString
+-- >
+-- > maybeMyFile :: Maybe Data.ByteString.ByteString
+-- > maybeMyFile = $(embedFileIfExists "dirName/fileName")
+embedFileIfExists :: FilePath -> Q Exp
+embedFileIfExists fp = do
+  mbs <- runIO maybeFile
+  case mbs of
+    Nothing -> [| Nothing |]
+    Just bs -> do
+#if MIN_VERSION_template_haskell(2,7,0)
+      qAddDependentFile fp
+#endif
+      [| Just $(bsToExp bs) |]
+  where
+    maybeFile :: IO (Maybe B.ByteString)
+    maybeFile = 
+      either (const Nothing) Just <$> 
+      tryJust (guard . isDoesNotExistError) (B.readFile fp)
+
 -- | Embed a single existing file in your source code
 -- out of list a list of paths supplied.
 --

file-embed.cabal

@@ -33,6 +33,7 @@ test-suite test
     main-is: main.hs
     hs-source-dirs: test
     build-depends: base
+                 , bytestring
                  , file-embed
                  , filepath
 

test/main.hs

@@ -2,6 +2,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 
 import Control.Monad (unless)
+import qualified Data.ByteString as B (ByteString, filter)
 import Data.FileEmbed
 import System.FilePath ((</>))
 
@@ -19,3 +20,9 @@ main = do
         ]
     let str = $(embedStringFile "test/sample/foo") :: String
     filter (/= '\r') str @?= "foo\n"
+
+    let mbs = $(embedFileIfExists "test/sample/foo")
+    fmap (B.filter (/= fromIntegral (fromEnum '\r'))) mbs @?= Just "foo\n"
+
+    let mbs2 = $(embedFileIfExists "test/sample/foo2") :: Maybe B.ByteString
+    mbs2 @?= Nothing