Incorrected code generated from SQL expressions type

If you install language-sqlite and add this module in QF:

```
{-# LANGUAGE TemplateHaskell, FlexibleInstances, ConstraintKinds #-}

module SQL where

import Test.QuickCheck
import Data.Binary( Binary(..), encode )
import Data.DeriveTH

import DeriveArbitrary
import ByteString
import Vector

import qualified Data.ByteString.Lazy as L
import qualified Data.ByteString.Lazy.Char8 as L8

import Language.SQL.SQLite
import Strings

$(devArbitrary ''Expression)

encode :: Expression -> L8.ByteString
encode x = L8.intercalate (L8.pack " ") $ map (L8.pack . show) $ showTokens x
```

will generate incorrect code (type error).