Re: parsing types

Dear Simon, Daniel and Thomas, thanks for your help with this! I managed to get what I want by writing something like so: tcExpr :: FilePath -> String -> IO Type tcExpr f s = defaultErrorHandler defaultDynFlags $ runGhc (Just libdir) $ do df <- getSessionDynFlags setSessionDynFlags df cm <- compileToCoreModule f setContext [(cm_module cm)] [] env <- getSession r <- hscTcExpr env s return r In short, I take the filepath, compile it to a module, then add that to the context and then extract the env and typecheck. If there's a shorter route, I'm all ears, but this seems to get the job done... Thanks again!, Ranjit. On Apr 26, 2011, at 3:13 AM, Simon Peyton-Jones wrote:

Ranjit

[NB: all of this is based on a quick look at the source code; I'm not that familiar with the GHC API, so others may correct me.]

A good entry point to the GHC API is InteractiveEval.hs. You'll see that all its functions are parameterised over a simple state monad (GhcMonad m), which is any monad supporting getSession :: m HscEnv setSession :: HscEnv -> m ()

The HscEnv encapsulates all the persistent state of the session, including the "ambient modules"; in a GHCi session these are the ones you have "imported" to the command line prompt.

You can augment these ambient modules with InteractiveEval.setContext. (Its API is a bit confusing and it's on my list of things to change.) So just call that to augment the context.

Then you can call hscTcExpr. [Maybe there should be a GhcMonad version of this function, with the type sig you give. The one in HscMain isn't.]

Does that help?

Simon

| -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell- | users-bounces@haskell.org] On Behalf Of Ranjit Jhala | Sent: 24 April 2011 02:27 | To: Daniel Peebles | Cc: ghc-users | Subject: Re: parsing types | | Hi Daniel -- | | that was a good lead, with a little digging around, I found | | hscTcExpr :: GhcMonad m => HscEnv -> String -> m Type | | which almost gets the job done, if only I could call it with | the appropriate HscEnv. The one I get using | | getSession :: GhcMonad m => m HscEnv | | appears rather impoverished, as it fails to find the usual | prelude names like | | Not in scope: `undefined' | Not in scope: `error' | | (though it does succeed on the expression "5" yielding the type) | | "forall t_a4eW. (GHC.Num.Num t_a4eW) => t_a4eW" | | Does anyone have a clue as to how to get a hold on an appropriate | environment? (I would have thought that the HscEnv obtained _after_ | compiling some file "f" would populated with at least the names | needed to compile "f") that is, if I do: | | cm0 <- compileToCoreSimplified f | env <- getSession | | then the resulting "env" would suffice, but unfortunately thats not | the case... | | Thanks!, | | Ranjit. | | | | | | | | | On Apr 23, 2011, at 11:54 AM, Daniel Peebles wrote: | | > I don't have an answer for you, but you might want to look at what :k does | in ghci, since that needs to parse a type. | > | > On Sat, Apr 23, 2011 at 2:06 PM, Ranjit Jhala wrote: | > Hi all, | > | > can someone give me a hint as to the best way to parse a type from a | string. | > Ideally, I'd like a function | > | > stringType :: String -> Maybe Type | > | > or possibly, | > | > stringType :: (GhcMonad m) => String -> m (Maybe Type) | > | > such that, | > | > stringType s == Just t | > | > if in the current GHC context the string s is the name of the type t. For | > example, I'd like: | > | > stringType "Int" | > | > to return a value equal to intTy (from TysWiredIn). My investigations have | > led me to | > | > parseType :: P (LHsType RdrName) | > | > and I suspect that with some work (mainly creating an appropriate PState, | > and mapping the name back, I can extract what I want, but I was wondering | > if there is some simpler route that I've overlooked. | > | > Thanks! | > | > Ranjit. | > | > _______________________________________________ | > Glasgow-haskell-users mailing list | > Glasgow-haskell-users@haskell.org | > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users | > | | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users