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RE: [Template-haskell] panic: addImpDecls
by Simon Peyton-Jones 23 Nov '04

23 Nov '04

Strange. GHC just doesn't allow nested declaration splices -- and gives a horrible message to boot. I'm not sure why I hadn't even registered that point. Turns out that the way to fix this is closely connected with preparatory work towards producing *typed* TH syntax trees. TH has grown quite a long to-do list in the last month. I'll try to do something about it before our Xmas release of 6.4. How urgent is this particular thing for you? Simon | -----Original Message----- | From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Ian Lynagh | Sent: 21 November 2004 23:59 | To: template-haskell(a)haskell.org | Subject: [Template-haskell] panic: addImpDecls | | | Hi all, | | If I have | | module Q () where | | $( [d| | $( [d| foo = 'c' |] ) | |] | ) | | or even | | module Q () where | | $( [d| | $( [] ) | |] | ) | | then "ghc -fth --make Q.hs" gives me: | | ghc-6.3: panic! (the `impossible' happened, GHC version 6.3): | addImpDecls | | | Thanks | Ian | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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RE: [Template-haskell] panic: addImpDecls
by Simon Peyton-Jones 23 Nov '04

23 Nov '04

| Is this preparatory work visible at all? Or still under wraps? Could | you explain the idea in a little more detail? Is this only for "closed" | declarations and expressions? It's not secret; it's just not implemented! Briefly the deal is this. Currently the type checker typechecks brackets, but throws the translated (type-annotated) term away. The desugarer translates the original un-annotated term. It'd be better to keep the translated term, so the desugarer could (if THSyntax supported types somehow) have access to the types. But the translated term is slightly mixed up: there are type abstractions and applications (easy to discard), but AbsBinds (the translation of a binding group) is a bit more of a problem. Anyway, it seems like the right way to go. Just need to find time to do it. Simon

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panic: addImpDecls
by Ian Lynagh 21 Nov '04

21 Nov '04

Hi all, If I have module Q () where $( [d| $( [d| foo = 'c' |] ) |] ) or even module Q () where $( [d| $( [] ) |] ) then "ghc -fth --make Q.hs" gives me: ghc-6.3: panic! (the `impossible' happened, GHC version 6.3): addImpDecls Thanks Ian

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RE: FW: [Template-haskell] TH restrictions
by Simon Peyton-Jones 19 Nov '04

19 Nov '04

| > Does anyone care? I'm busy implementing GADTs at the moment, so TH has a | > somewhat back seat. It'll probably stay that way unless there are some | > signs of life in the TH ranks. | | For what it's worth, I think one of the biggest irritations I've had | with writing stuff using TH is the need to split things across module | boundaries. This often leads to things that should logically be in the | same module being split I agree with this; I'd like to know how much it affects other people too. It's tricky to implement, though. I don't really want to compile each definition to byte code as we encounter it, just in case the next definition contains a splice. (That would slow down every single compilation, whether or not it used TH.) I guess I could look ahead to see if there was a splice in the next definition group, and if so compile the entire module up to that point. Even that isn't usually necessary, because the splice may not call anything defined earlier. Perhaps one could compute the transitive closure of things needed. So it'd be real work. What do others think? | Also, I think this has got worse at some point. Going back over some of | my old code it looks like this sort of thing: | | foo = and | bar = [| foo |] | | in one module used to be OK whereas now it gives | | No instance for (Language.Haskell.TH.Syntax.Lift ([Bool] -> Bool)) This looks like a bug -- I'll try to fix it. Simon

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Multi-stage programming examples
by Ian Lynagh 18 Nov '04

18 Nov '04

Hi all, I have ported a few small multi-state programming examples from MetaOCaml and put them at: http://www.haskell.org/th/examples/msp_ex.tar.gz Thanks Ian

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Problem with TH
by Keean Schupke 18 Nov '04

18 Nov '04

I am using the new existential datatype support (great!) - but now when I patch in fundep support (more or less as I posted before) adding an extra field to ClassD, I have to modify GHC to use the extra field in ClassD... Now when I include a definition: [d| class Test x |] I get the error: ghc-6.3: panic! (the `impossible' happened, GHC version 6.3): deSugar/DsMeta.hs:925:4-41: Irrefutable pattern failed for pattern [elt_ty] Any idea why this might be happening (why is the error in DsMeta, when the TH stuff is in hsSyn/Convert.lhs and typecheck/TcSplice.lhs? Keean.

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Re: [Template-haskell] Re: template haskell (reify bug and existentials)
by Keean Schupke 08 Nov '04

08 Nov '04

Ian Lynagh wrote: >On Wed, Nov 03, 2004 at 10:17:04AM +0000, Keean Schupke wrote: > > >>Ian Lynagh wrote: >> >> >> >>>>in Syntax.hs: >>>> ... >>>> type Fundep = ([Name],[Name]) -- add to export list >>>> >>>> Have you made a decision regarding FunDeps yet? Keean.

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Re: [Template-haskell] RE: TH2 bug
by MR K P SCHUPKE 03 Nov '04

03 Nov '04

>(i.e. DataD with all the stuff that doesn't occur removed)? Yes, this sounds good to me... effectively we just want the left hand side of the 'data' statement defining them. As they are primitves the right hand side is unknowable (ie they behave as abstract types) Keean.

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RE: TH2 bug
by Simon Peyton-Jones 03 Nov '04

03 Nov '04

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(a)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(a)haskell.org, | >| or http://sourceforge.net/projects/ghc/. | >| | >| | >| Keean. | > | >

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template haskell (reify bug and existentials)
by Keean Schupke 03 Nov '04

03 Nov '04

Re: my two earlier postings: 1) existentials in data declarations. I have a project which needs this, Simon PJ thought it was fairly easy to put in and suggested that Ian Lynagh might implement it. Do I need to persuade people further? Will it get done now? Some feedback as to whether it might get done would be nice... Just to clarify I want to do: $(something [d| data A = forall a . A a |] 2) reification of functions (and other primitives)... want to do something like: reify ''(->) Fails because reify/Info does not support reifying primitives. There is already support in the Type type for primitive types (-> (,,) []) so the obvious way to add this is to alter Info to: data Info = ClassI Dec | ClassOpI Name Type Name Fixity | TyConI Dec | PrimTyConI Type | DataConI ... So what are the chances of getting these changes implemented. I need them for a current project, and would appreciate it if someone who knows the inner workings of template-haskell could implement the changes in the CVS HEAD branch of GHC. Failing that I am prepared to have a go myself, but I want to make sure that nobody else is likely to do it first.

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