[Change type of checkBidirectionalizability to return Maybe String
Joachim Breitner <mail@joachim-breitner.de>**20100913201313
 Ignore-this: e2177ce315a814ca9c75f445988f1126
] hunk ./SemSyn.hs 175
-checkBidirectionalizability :: AST -> AST 
+checkBidirectionalizability :: AST -> Maybe String 
hunk ./SemSyn.hs 178
-      (Nothing, Nothing) -> ast
-      (Just (e,d),Nothing)       -> error $ showTreelessError (e,d) 
-      (Nothing, Just (vs,d'))    -> error $ showAffineError   (vs,d')
-      (Just (e,d), Just (vs,d')) -> error $ showTreelessError (e,d) ++ "\n" ++ showAffineError (vs,d') 
+      (Nothing, Nothing) -> Nothing
+      (Just (e,d),Nothing)       -> Just $ showTreelessError (e,d) 
+      (Nothing, Just (vs,d'))    -> Just $ showAffineError   (vs,d')
+      (Just (e,d), Just (vs,d')) -> Just $ showTreelessError (e,d) ++ "\n" ++ showAffineError (vs,d')