Initial change to permit use of inline template haskell, to address

issue: https://github.com/gibiansky/IHaskell/issues/236

To verify functionality, paste the following into a code block in
IHaskell.

```
:ext TemplateHaskell
import Language.Haskell.TH
import Control.Lens
data Foo a = Foo { _bar :: Int, _baz :: Int, _quux :: a }
makeLenses ''Foo
:ty baz
```

ihaskell.cabal

@@ -85,6 +85,7 @@ library
                        system-argv0         -any,
                        system-filepath      -any,
                        tar                  -any,
+                       template-haskell     -any, 
                        text                 >=0.11,
                        transformers         -any,
                        unix                 >= 2.6,

src/IHaskell/Eval/Evaluate.hs

@@ -20,6 +20,7 @@ import Data.Char as Char
 import Data.Dynamic
 import Data.Typeable
 import qualified Data.Serialize as Serialize
+import qualified Language.Haskell.TH as TH  
 import System.Directory
 import Filesystem.Path.CurrentOS (encodeString)
 import System.Posix.IO
@@ -704,8 +705,20 @@ evalCommand output (Expression expr) state = do
   let widgetExpr = printf "(IHaskell.Display.Widget (%s))" expr :: String
   isWidget <- attempt $ exprType widgetExpr
 
+  -- Check if this is a declaration  
+ -- let declExpr = printf "((id :: Q [Dec] -> Q [Dec]) (%s))" expr::String
+  let declExpr = printf "((id :: DecsQ -> DecsQ) (%s))" expr::String
+  isDeclaration <- attempt $ exprType declExpr  
+
   write $ "Can Display: " ++ show canRunDisplay
-  write $ "  Is Widget: " ++ show canRunDisplay
+  write $ "  Is Widget: " ++ show isWidget 
+  if isDeclaration 
+  then do 
+      write $ "  Is Declaration: " ++ show isDeclaration 
+      (GHC.runDecls expr) >> return ()  
+  else  
+      write $ "  Is Declaration:" ++ show isDeclaration 
+
 
   if canRunDisplay
   then do
@@ -716,7 +729,18 @@ evalCommand output (Expression expr) state = do
     if isWidget
     then registerWidget out
     else return out
-
+  else do
+    if isDeclaration 
+    -- We do not want to display the DecsQ, we just want the 
+    -- declaration made. 
+    then do write $ "Suppressing display for template haskell declaration"  
+            return EvalOut {
+                    evalStatus = Success,
+                    evalResult = mempty,  
+                    evalState = state,
+                    evalPager = "",
+                    evalComms = []
+                }
     else do  
             -- Evaluate this expression as though it's just a statement.
             -- The output is bound to 'it', so we can then use it.