parsing types

[Simon Peyton-Jones]

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 at 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 at haskell.org [mailto:glasgow-haskell-
| > | users-bounces at 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 at 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 at haskell.org
| > | > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
| > | >
| > |
| > |
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