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 <jhala@cs.ucsd.edu> 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.

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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 <jhala@cs.ucsd.edu> 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

Ah, well, yes, if you want to get an existing, *uncompiled* module into the ambient context, then of course you must compile it. Glad you are unstuck. Simon | -----Original Message----- | From: Ranjit Jhala [mailto:rjhala@eng.ucsd.edu] On Behalf Of Ranjit Jhala | Sent: 27 April 2011 00:42 | To: Simon Peyton-Jones; Daniel Peebles; Thomas Schilling | Cc: ghc-users | Subject: 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 <jhala@cs.ucsd.edu> | 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 | > |