Add in json2yaml

exe/json2yaml.hs

@@ -0,0 +1,25 @@
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances #-}
+import System.Environment (getArgs)
+import qualified Data.Aeson as J
+import qualified Data.Yaml as Y
+import Control.Monad (when)
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Lazy as L
+import Control.Applicative ((<$>))
+
+main :: IO ()
+main = do
+    args <- getArgs
+    when (length args > 2) $ error "Usage: json2yaml [in] [out]"
+    let (input:output:_) = args ++ repeat "-"
+    mval <- J.decode <$>
+        case input of
+            "-" -> L.getContents
+            _ -> L.readFile input
+    case mval of
+        Nothing -> error "Invalid input JSON"
+        Just val -> do
+            case output of
+                "-" -> S.putStr $ Y.encode (val :: Y.Value)
+                _ -> Y.encodeFile output val

yaml.cabal

@@ -1,5 +1,5 @@
 name:            yaml
-version:         0.8.7.2
+version:         0.8.8
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>, Anton Ageev <antage@gmail.com>,Kirill Simonov 
@@ -30,7 +30,7 @@ extra-source-files: c/helper.h,
                     test/json.yaml
 
 flag no-exe
-  description: don't install the yaml2json executable
+  description: don't install the yaml2json or json2yaml executables
   default: False
 
 flag system-libyaml
@@ -84,6 +84,19 @@ executable yaml2json
                  , bytestring >= 0.9.1.4
                  , aeson >= 0.5
 
+executable json2yaml
+    if flag(no-exe)
+      Buildable: False
+    else
+      Buildable: True
+
+    hs-source-dirs: exe
+    main-is: json2yaml.hs
+    build-depends: base >= 4 && < 5
+                 , yaml
+                 , bytestring >= 0.9.1.4
+                 , aeson >= 0.5
+
 
 test-suite test
     type: exitcode-stdio-1.0