Stub in a Fix type for the sake of experimentation.

src/Alignment.hs

@@ -104,3 +104,6 @@ openRange source range = (at source <$> maybeLastIndex range) /= Just '\n'
 
 -- | A row in a split diff, composed of a before line and an after line.
 type Row a = Both (Line a)
+
+-- | A fixpoint over a functor.
+newtype Fix f = Fix { unFix :: f (Fix f) }