Deal with small -fcontext-stack on ghc-7.8

Use default value from ghc-7.10, i.e 100.

ihaskell-display/ihaskell-widgets/ihaskell-widgets.cabal

@@ -91,3 +91,6 @@ library
   -- Base language which the package is written in.
   default-language:    Haskell2010
   
+  -- Deal with small -fcontext-stack on ghc-7.8
+  if impl(ghc == 7.8.*)
+    ghc-options:       -fcontext-stack=100

ihaskell-display/ihaskell-widgets/src/IHaskell/Display/Widgets/Image.hs

@@ -17,6 +17,7 @@ import           Control.Monad (when, join)
 import           Data.Aeson
 import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
+import           Data.Monoid (mempty)
 import           Data.Text (Text)
 import           Data.Vinyl (Rec (..), (<+>))
 

src/IHaskell/Eval/Evaluate.hs

@@ -239,6 +239,10 @@ initializeImports = do
   imports <- mapM parseImportDecl $ globalImports ++ displayImports
   setContext $ map IIDecl $ implicitPrelude : imports
 
+  -- Set -fcontext-stack to 100 (default in ghc-7.10). ghc-7.8 uses 20, which is too small.
+  let contextStackFlag = printf "-fcontext-stack=%d" (100 :: Int)
+  void $ setFlags [contextStackFlag]
+
 -- | Give a value for the `it` variable.
 initializeItVariable :: Interpreter ()
 initializeItVariable =