Cool, that means I can derive instances of TTypeable (type level type rep) for primitive types... Keean. Simon Peyton-Jones wrote:
Did I mention that I've committed this change.
| PrimTyConI -- Ones that can't be expressed with a data type -- decl, such as (->), Int# Name Int -- Arity Bool -- False => lifted type; True => unlifted
| -----Original Message----- | From: template-haskell-bounces@haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Keean Schupke | Sent: 27 October 2004 15:12 | To: Keean Schupke | Cc: template-haskell@haskell.org; Simon Peyton-Jones | Subject: Re: [Template-haskell] Re: TH2 bug | | Just checked and 'Type' has an entry (ArrowT) for functions. | Why not just use the existing Type. IE | | reify ''(->) | | data Info = | PrimTyCon Type | TyConI Dec | | This would be fine for tuples as well, I wonder if () could be | encoded as a tuple of 0? | | Keean. | | Keean Schupke wrote: | | > Actually I would like it to be a special name... but I guess there | > are other possibilities. | > | > Ideally I would like: | > | > case info of | > (PrimTyCon name) -> instanceD (cxt []) (appT (conT classname) (appT | > (appT (conT name) (varT a) (varT b))) | > | > to generate: | > | > instance ClassName (a -> b) | > | > | > Keean | > | > Simon Peyton-Jones wrote: | > | >> OK, now I get it. I'm copying the TH list in the hope that other TH | >> aficionados will chime in. | >> | >> The problem is with reify, not the '' notation. Here it is in a | >> nutshell: | >> what value should be returned by the call (reify ''(->) )? | >> | >> Recall that | >> reify :: Name -> Q Info | >> | >> So reify claims to return an Info, and for a type constructor it | >> currently returns a TyConI; but a TyConI contains a Dec, and there | >> simply is no Dec in the TH syntax for a function type; it's built in, | >> rather like Int# etc. So reify falls over in a bad way. | >> | >> It's obviously unsatisfactory for reify to just fall over in this case, | >> but what would you like? A new constructor in Info for primitive | >> tycons? A new constructor in Dec? | >> And what questions do you want to be able to ask of the value in the | >> Info? For example would it be enough to day | >> | >> data Info = TyConI Dec | >> | PrimTyCon | >> | ClassI Dec | >> ...etc... | >> | >> where the PrimTyCon is returned for (->), Int#, etc? | >> | >> Nothing difficult about fixing this once the design is clear. | >> | >> Simon | >> | >> | -----Original Message----- | >> | From: Keean Schupke [mailto:k.schupke@imperial.ac.uk] | >> | Sent: 27 October 2004 11:14 | >> | To: Simon Peyton-Jones | >> | Subject: Re: TH2 bug | >> | | Yup, using HEAD. Here's an example template: | >> | | ttypeshow :: Name -> Q [Dec] | >> | ttypeshow q = do | >> | r <- reify q | >> | case r of | >> | (TyConI t) -> runIO . putStrLn . show $ t | >> | _ -> return () | >> | return [] | >> | | Then in another file we do: | >> | | $(ttypeshow ''(->)) | >> | | Which fails, as does ''(), and ''(,) etc... | >> | | ''[] works okay however | >> | | Keean. | >> | | | Simon Peyton-Jones wrote: | >> | | >I can't reproduce this. Works for me. What version of GHC are you | >> | >using? The HEAD I assume? | >> | > | >> | >Simon | >> | > | >> | >| -----Original Message----- | >> | >| From: MR K P SCHUPKE [mailto:k.schupke@imperial.ac.uk] | >> | >| Sent: 22 October 2004 18:23 | >> | >| To: glasgow-haskell-users@haskell.org; Simon Peyton-Jones | >> | >| Subject: TH2 bug | >> | >| | >> | >| | >> | >| Just reporting a bug, taking types using '' works fine for: | >> | >| | >> | >| ''Int | >> | >| ''[] | >> | >| | >> | >| But when you try: | >> | >| | >> | >| ''(->) | >> | >| | >> | >| you get: | >> | >| | >> | >| No match in record selector TyCon.algTcRhs | >> | >| | >> | >| Please report it as a compiler bug to | >> | >glasgow-haskell-bugs@haskell.org, | >> | >| or http://sourceforge.net/projects/ghc/. | >> | >| | >> | >| | >> | >| Keean. | >> | > | >> | > | >> | >> | >> | > | > _______________________________________________ | > template-haskell mailing list | > template-haskell@haskell.org | > http://www.haskell.org/mailman/listinfo/template-haskell | | | _______________________________________________ | template-haskell mailing list | template-haskell@haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell