generate completions on the ghc-side, doesn't get interpreted correctly yet

see note in Completion.hs

IHaskell.cabal

@@ -70,6 +70,8 @@ executable IHaskell
                        ghc ==7.6.*,
                        ghc-paths ==0.1.*,
                        random ==1.0.*,
+                       split,
+                       utf8-string,
                        strict ==0.3.*,
                        shelly ==1.3.*,
                        text ==0.11.*

IHaskell/Completion.hs

+{-# LANGUAGE PatternGuards #-}
+{- | very approximate completion. Seems to generate what is required by
+ <http://ipython.org/ipython-doc/dev/development/messaging.html#complete>,
+ but for whatever reason nothing gets added when the liftIO below prints
+ stuff like:
+
+ > {"status":"ok","text":"import Data hea","matches":["head"]}
+
+ When the cursor is after the hea, and you press tab.
+-}
+module IHaskell.Completion (makeCompletions) where
+
+import Prelude
+import Data.List
+import IHaskell.Types
+import GhcMonad(liftIO)
+import qualified GHC
+import Outputable (showPpr)
+import Data.Char
+import Data.ByteString.UTF8
+import Data.List.Split
+import Data.List.Split.Internals
+import Data.Aeson
+import IHaskell.Message.Writer
+import qualified Data.ByteString.Lazy as L
+
+makeCompletions replyHeader (CompleteRequest hdr code line pos) = do
+
+    ns <- GHC.getRdrNamesInScope
+    fs <- GHC.getProgramDynFlags
+
+    let candidate = getWordAt (toString line) pos
+        opts | Just cand <- candidate = filter (cand `isPrefixOf`) $ map (showPpr fs) ns
+            | otherwise = []
+
+    let reply = CompleteReply replyHeader (map fromString opts) line True
+    liftIO (L.putStrLn $ encode $ toJSON reply)
+    return reply
+
+
+-- there are better ways to accomplish this
+getWordAt :: String -> Int -> Maybe String
+getWordAt xs n =
+        fmap (map fst) $
+        find (any (== n) .  map snd) $
+        split (defaultSplitter{
+                        delimiter = Delimiter [ (==) ' ' . fst ],
+                        condensePolicy = Condense })
+                (zip xs [1 .. ])
+

Main.hs

@@ -12,6 +12,7 @@ import qualified IHaskell.Message.UUID as UUID
 import IHaskell.Eval.Evaluate
 import qualified Data.ByteString.Char8 as Chars
 import IHaskell.IPython
+import IHaskell.Completion (makeCompletions)
 
 data KernelState = KernelState
   { getExecutionCounter :: Int
@@ -147,7 +148,8 @@ replyTo interface ExecuteRequest{ getCode = code } replyHeader state = do
   })
 
 
-replyTo _ cr@CompleteRequest{} replyHeader state = trace (show cr) $ do
-    return (state,  CompleteReply replyHeader []  "" True)
+replyTo _ creq@CompleteRequest{} replyHeader state = trace (show creq) $ do
+    cr <- makeCompletions replyHeader creq
+    return (state,  cr)