GHC's parse tree contains lots of placeholders. You are not supposed
to look at them until a specific phase has been run. For example,
anything of type "SyntaxExpr" is an error thunk until the renamer has
been run. Unfortunately, SyntaxExpr is just a type synonym, so
there's no way to distinguish them via SYB.
The simplest workaround is to adapt the default traversal code for the
nodes which may contain such error thunks. A better solution would be
to change the GHC AST to wrap such possibly undefined nodes with
newtypes, but that would only take effect once the next version of GHC
is released.
On 24 August 2011 23:11, Simon Hengel
Hello, I'm trying to query a type-checked module with syb, this works for a plain binding. But as soon as I add a type signature for that binding, I get an "panic!"
I experienced similar problems with a renamed module.
Are those data structures meant to be used with syb? And if yes, what did I miss?
Bellow is some code to reproduce my issue. Any help is very much appreciated.
-- A.hs module Main where
import GHC import Outputable import Data.Generics import GHC.Paths (libdir)
import Bag
main :: IO () main = do m <- parse putStrLn $ showSDoc $ ppr $ m putStrLn "\n---\n" putStrLn $ showSDoc $ ppr $ selectAbsBinds m
parse = runGhc (Just libdir) $ do _ <- getSessionDynFlags >>= setSessionDynFlags target <- guessTarget "B.hs" Nothing setTargets [target] Succeeded <- load LoadAllTargets modSum <- getModSummary $ mkModuleName "B" m <- parseModule modSum >>= typecheckModule return $ typecheckedSource m
selectAbsBinds :: GenericQ [HsBindLR Id Id] selectAbsBinds = everything (++) ([] `mkQ` f) where f x@(AbsBinds _ _ _ _ _) = [x] f _ = []
-- B.hs module B where
foo :: Char foo = 'f'
Cheers, Simon
_______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
-- Push the envelope. Watch it bend.