Fix error display when compiling/linking shaders

src/Shader/Compile.hs

@@ -19,6 +19,7 @@ import Shader.Data
 import Shader.Parameters
 
 import Foreign
+import Foreign.C.String
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Unsafe as BU
 import Control.Monad
@@ -345,10 +346,10 @@ makeShaderProgram' str srcs = do
     mapM_ glDeleteShader shaders
     return theprog
     
-glCheckError :: (Storable t1, Storable a1, Show a1) =>
+glCheckError :: (Storable t1) =>
                 [Char]
                 -> (t2 -> GLenum -> Ptr t1 -> IO ())
-                -> (t2 -> t1 -> Ptr a3 -> Ptr a1 -> IO ())
+                -> (t2 -> t1 -> Ptr a3 -> CString -> IO ())
                 -> t2
                 -> GLenum
                 -> IO ()
@@ -363,7 +364,7 @@ glCheckError str f g x statustype =
                     len <- peek ptr -- we may have to use this length more intelligently
                     alloca $ \charPtr -> do
                         g x len nullPtr charPtr
-                        char <- peek charPtr
+                        char <- peekCString charPtr
                         error $ str ++ show char
             else return ()