December 2004 - template-haskell

Using arrowT in a constructor class
by Peter Gammie 14 Dec '04

14 Dec '04

(I'm using GHC 6.2.2 on SPARC/Solaris.) I've got a class: class (Arrow arrow) => ArrowComb arrow b where or2 :: arrow (b, b) b ... and want to make an instance for it: data DCin b = MkDCin { field :: b } instance ArrowComb (->) b => ArrowComb (->) (DCin b) where or2 = ... using Template Haskell. Trying to use "arrowT" as a constructor in this context leads to the runtime error: *** Exception: hsSyn/Convert.lhs:317: Non-exhaustive patterns in function trans I can provide a test case if you need one. I don't have access to a CVS version, so this may already have been fixed. regards, Peter.

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Show Info
by Jim Apple 14 Dec '04

14 Dec '04

Is there any reason why Info isn't deriving(Show) ? Jim Apple

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FW: [Template-haskell] RE: calling fail in Q monad gives uninformativeerror message, anderror causes panic
by Simon Peyton-Jones 05 Dec '04

05 Dec '04

Dear Template Haskell colleagues I sent three messages to the TH list a month ago. Here's one of them: the others concerned the conversions TH.Syntax <-> HsSyn; I'll fwd them in the next two messages I didn't get a single reply to any of the three. Either the TH mailing list is broken, or else you are all busy with other stuff. (After all, all three did ask for volunteers, in one form or another.) 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. Simon -----Original Message----- From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On Behalf Of Simon Peyton-Jones Sent: 20 July 2004 12:19 To: Duncan Coutts; Template Haskell List Subject: [Template-haskell] RE: calling fail in Q monad gives uninformativeerror message, anderror causes panic Tim and I want to tidy up the error-reporting interface in Template Haskell. The goal is that a TH user should be able to control the error messages that appear. Here's a proposal qReport :: Severity -> String -> Q () -- Report an error or warning -- ...but carry on; use 'fail' to stop fail :: String -> Q a -- Part of Monad class qRecover :: (String -> [(Severity,Loc,String)] -> Q a) -> Q a -> Q a -- Recover from the monadic 'fail' -- The first arg is the error handler -- The first String arg to the handler is what was passed to 'fail' qReports :: [(Severity,Loc,String)] -> Q () data Severity = Error | Warning qGetLoc :: Q Loc qGetModule :: Q ModuleName qWithLoc :: Loc -> Q a -> Q a data Loc = Loc FileName LineNumber CharPos The idea is that qReport dumps a message into the monad (but does not print it yet) with an indication of severity. qReport does not cause monadic failure... you can dump in as many error messages as you like. qReport adds location information from the monad to the message. fail causes monadic failure. qRecover recovers from monadic failure, giving to the recovery routine both the string passed to fail, and the accumulated messages from the enclosed computation. It can use qReports to dump all those messages back into the monad -- or it can just discard them if it wants. At a splice point, the typechecker runs the Q computation. If the result is monadic success, it continues with the returned results. If the result is monadic failure, the splice fails too. (That does not result in any panic -- the type checker is designed to fail, and recover at some outer point.) In both cases, the messages from the Q monad are dumped into the typechecker's message pile. One open question. If you say qReport Error "Bad thing" fail "wuggle" in the Q monad, do you get two type error messages ("Bad thing" and "wuggle") or just one? I can think of three possibilities a) fail s is treated as adding an error message with Severity = Error b) fail s adds no error messages c) fail s behaves like (b) if (null s) and like (a) otherwise. The advantage of (b) and (c) is that you can add a whole bunch of error messages, and then fail, without adding yet another. Comments? Once we have an interface agreed, it won't be hard to implement. Simon | -----Original Message----- | From: glasgow-haskell-bugs-bounces(a)haskell.org [mailto:glasgow-haskell-bugs- | bounces(a)haskell.org] On Behalf Of Duncan Coutts | Sent: 23 June 2004 01:13 | To: glasgow-haskell-bugs(a)haskell.org | Subject: TH: calling fail in Q monad gives uninformative error message, anderror causes panic | | | ghc makes it's own type checker monad TcM an instance of the Quasi class | (which is rather cunning), however this means that if the user calls the | Monad function 'fail' then the internal TcM fail method gets called. | This monad (IOEnv) was never meant to fail (see | ghc/compiler/utils/IOEnv.hs/) so the error message is: | | Exception when trying to run compile-time code: | Code: genex_count | Exn: user error (IOEnv failure) | | Of course the user code should be using 'report', but if you're using | old code, or code that is generic in the monad it uses then people will | end up calling fail. | | Perhaps the thing to do is to wrap splices in an exception handler and | convert 'fail's into a 'report' instead. | | The same should probably be done for errors raised in pure code by | calling 'error'. At the moment it gives an overly panicky report | (although at least it passes the user's error message through): | | ghc-6.3: panic! (the `impossible' happened, GHC version 6.3): | where clauses & gaurds not yet supprted in function definitions | | The error message there is generated by my code (hence the spelling | errors :-) ). | | Duncan | | _______________________________________________ | Glasgow-haskell-bugs mailing list | Glasgow-haskell-bugs(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs _______________________________________________ template-haskell mailing list template-haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/template-haskell

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RE: template haskell printf doesn't compile...
by Simon Peyton-Jones 05 Dec '04

05 Dec '04

Redirecting this to the Template Haskell mailing list Guys, can you help Alex? Simon | -----Original Message----- | From: S. Alexander Jacobson [mailto:alex@alexjacobson.com] | Sent: 03 December 2004 16:59 | To: Simon Peyton-Jones | Cc: GHC users | Subject: RE: template haskell printf doesn't compile... | | I was able to use the library documentation to get | printf to compile. But I still can't figure out | how to produce Declarations. Is there a directory | somewhere with more examples? | | Note this is being used to overhaul my relational | database code. | | -Alex- | | ______________________________________________________________ | S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com | | | | On Fri, 3 Dec 2004, Simon Peyton-Jones wrote: | | > Sorry Documentation out of date: consult the library documentation for | > up to date info. | > | > Change Expr to ExpQ | > change string to stringE | > | > | -----Original Message----- | > | From: glasgow-haskell-users-bounces(a)haskell.org | > [mailto:glasgow-haskell-users- | > | bounces(a)haskell.org] On Behalf Of S. Alexander Jacobson | > | Sent: 02 December 2004 20:21 | > | To: GHC users | > | Subject: template haskell printf doesn't compile... | > | | > | Tried to use the printf TH example described in | > | the GHC docs | > | | > | | > http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell | > .html | > | | > | Got this error: | > | | > | Chasing modules from: PrintMain.hs | > | Compiling Printf ( ./Printf.hs, ./Printf.o ) | > | | > | ./Printf.hs:23: Type constructor or class not in scope: `Expr' | > | | > | ./Printf.hs:26: Variable not in scope: `string' | > | ./Printf.hs:30: Type constructor or class not in scope: `Expr' | > | | > | Any clues? | > | | > | -Alex- | > | | > | ______________________________________________________________ | > | S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com | > | _______________________________________________ | > | Glasgow-haskell-users mailing list | > | Glasgow-haskell-users(a)haskell.org | > | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users | > _______________________________________________ | > Glasgow-haskell-users mailing list | > Glasgow-haskell-users(a)haskell.org | > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users | >

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RE: [Template-haskell] Re: template-haskell names in 6.3
by Simon Peyton-Jones 03 Dec '04

03 Dec '04

do you mean n <- newName s or let n = mkName s ? If the former, you'll get a new decl like data Foo_24 = Foo_098 Foo_24 which definitely won't clash. We discussed this, and I've implemented it. If the latter, you will get data Foo = Foo Foo ... and then I see what you want. You want a version of mkName that is like giving a qualified name in Haskell. It's dynamically scoped just like mkName, but it obeys the usual rules for qualified names in Haskell. To be totally explicit, suppose I have foo = [| mkQualName "Foo" "baz" |] then if I call foo thus wibble = \baz -> $foo the $foo splice will expand to "Foo.baz", and that won't see the \baz; it'll see whatever Foo.baz is in scope. Is that what you seek? I can see it's reasonable. I'd need to add mkQualName :: String -> String -> Name That'd mean an extra form of Name. Currently, if you say 'Foo.baz you'll get a Name whose nameModule isn't necessarily Foo... it'll be the module that baz was actually defined in. Simon | -----Original Message----- | From: Keean Schupke [mailto:k.schupke@imperial.ac.uk] | Sent: 03 December 2004 13:09 | To: Simon Peyton-Jones | Subject: Re: [Template-haskell] Re: template-haskell names in 6.3 | | Okay, | | makeDecl :: String -> DecQ | makeDecl s = do | n <- mkName s | dataD (cxt []) n [] [normalC n [(NotStrict,ConT n)]] | | $(makeDecl "Foo") | | will give: | | data Foo = Foo Foo | | what I want is: | | makeDecl :: String -> DecQ | makeDecl s = do | n <- mkName s | m <- qCurrentModule | n' <- mkNameG m s | dataD (cxt []) n [] [normalC n [(NotStrict,ConT n')]] | | $(makeDecl "Foo") -- now gives: | | data Foo = Foo Module.Foo | | to disambiguate from OtherModule.Foo | | Keean. | | Simon Peyton-Jones wrote: | | >But you used newName to generate the data type, so you do have the | >name.! | > | >I guess the only way to understand this is for you to give a small TH | >program that demonstrates the problem | > | >| -----Original Message----- | >| From: Keean Schupke [mailto:k.schupke@imperial.ac.uk] | >| Sent: 03 December 2004 12:28 | >| To: Simon Peyton-Jones | >| Subject: Re: [Template-haskell] Re: template-haskell names in 6.3 | >| | >| Simon Peyton-Jones wrote: | >| | >| Lets say we want to generate a recursive datatype, where there may | >already | >| be a name in scope from another module... we need: | >| | >| data Foo a = MkFoo (Module.Foo a) | >| | >| but we cannot use ''Foo to get the name as foo is not in scope yet. | >| | >| Keean. | >| | >| >now you've lost me. Just declare the constructor at the top level, | >and | >| >it'll get a global name. | >| > | >| >I don't see why you would ever want to make global name yourself. In | >| >Haskell we don't say | >| > | >| > data Foo.T = ... | >| > | >| >we just say | >| > | >| > data Foo = ... | >| > | >| >Simon | >| > | >| > | > | > | >

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RE: [Template-haskell] Re: TH2 bug
by Simon Peyton-Jones 03 Dec '04

03 Dec '04

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(a)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(a)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(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. | >> | > | >> | > | >> | >> | >> | > | > _______________________________________________ | > template-haskell mailing list | > template-haskell(a)haskell.org | > http://www.haskell.org/mailman/listinfo/template-haskell | | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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RE: [Template-haskell] Re: template-haskell names in 6.3
by Simon Peyton-Jones 03 Dec '04

03 Dec '04

Reasonable idea. I've added nameModule :: Name -> Maybe String to join the existing nameBase :: Name -> String The 'Maybe' is needed because not all names have modules; in particular, ones that are made with mkName or newName. OK? Simon | -----Original Message----- | From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Keean Schupke | Sent: 03 December 2004 11:00 | To: Simon Peyton-Jones | Cc: template-haskell(a)haskell.org | Subject: [Template-haskell] Re: template-haskell names in 6.3 | | Simon Peyton-Jones wrote: | | Right... I had a good look through the library source, but must have | missed it... | It seems the functions to build and extract the 'module' part of Names | is not | exported... is there any reason why it can't be? | | Keean. | | >Acutally it's there already: | > qCurrentModule :: Q String | > | >Simon | > | >| -----Original Message----- | >| From: Keean Schupke [mailto:k.schupke@imperial.ac.uk] | >| Sent: 02 December 2004 17:37 | >| To: Simon Peyton-Jones | >| Subject: Re: template-haskell names in 6.3 | >| | >| Simon Peyton-Jones wrote: | >| | >| Okay I want a globaly unique label, so I want to prepend the module | >name | >| to the string... | >| | >| module SomeLib.MyModule where | >| | >| $(label "myLabel") -- splices: myLabel = "SomeLib.MyModule.myLabel" | >| | >| I guess what I want is a reifyModuleName? | >| | >| Keean. | >| | >| >| -----Original Message----- | >| >| From: MR K P SCHUPKE [mailto:k.schupke@imperial.ac.uk] | >| >| Sent: 22 October 2004 13:05 | >| >| To: glasgow-haskell-users(a)haskell.org; Simon Peyton-Jones | >| >| Subject: template-haskell names in 6.3 | >| >| | >| >| | >| >| I have now read most of the notes on template-haskell2, but I still | >| >| have a problem with naming (although I think my issues with types | >| >| are adequately dealt with by the '' notation. | >| >| | >| >| I wish to create a declaration in template haskell, where the | >funtion | >| >| name is supplied: something like: | >| >| | >| >| $(label "myLabel") | >| >| | >| >| However I wish the reference to this label to be globally specific | >| >| to the generated instance... an example of this would be a function | >| >| that prints its reified name: | >| >| | >| >| $(example "myLabel") would splice: | >| >| | >| >| myLabel :: String | >| >| myLabel = "This_module.myLabel" | >| >| | >| >| mkName only returns the 'local' namem | >| >| how can I get a global name from a string? | >| >| | >| >| Keean. | >| > | >| > | > | > | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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RE: template-haskell names in 6.3
by Simon Peyton-Jones 03 Dec '04

03 Dec '04

Acutally it's there already: qCurrentModule :: Q String Simon | -----Original Message----- | From: Keean Schupke [mailto:k.schupke@imperial.ac.uk] | Sent: 02 December 2004 17:37 | To: Simon Peyton-Jones | Subject: Re: template-haskell names in 6.3 | | Simon Peyton-Jones wrote: | | Okay I want a globaly unique label, so I want to prepend the module name | to the string... | | module SomeLib.MyModule where | | $(label "myLabel") -- splices: myLabel = "SomeLib.MyModule.myLabel" | | I guess what I want is a reifyModuleName? | | Keean. | | >| -----Original Message----- | >| From: MR K P SCHUPKE [mailto:k.schupke@imperial.ac.uk] | >| Sent: 22 October 2004 13:05 | >| To: glasgow-haskell-users(a)haskell.org; Simon Peyton-Jones | >| Subject: template-haskell names in 6.3 | >| | >| | >| I have now read most of the notes on template-haskell2, but I still | >| have a problem with naming (although I think my issues with types | >| are adequately dealt with by the '' notation. | >| | >| I wish to create a declaration in template haskell, where the funtion | >| name is supplied: something like: | >| | >| $(label "myLabel") | >| | >| However I wish the reference to this label to be globally specific | >| to the generated instance... an example of this would be a function | >| that prints its reified name: | >| | >| $(example "myLabel") would splice: | >| | >| myLabel :: String | >| myLabel = "This_module.myLabel" | >| | >| mkName only returns the 'local' namem | >| how can I get a global name from a string? | >| | >| Keean. | > | >

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RE: [Template-haskell] Bug? Unique class names...
by Simon Peyton-Jones 02 Dec '04

02 Dec '04

I've just committed a fix for this. SImon | -----Original Message----- | From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Keean Schupke | Sent: 26 November 2004 11:09 | To: Ian Lynagh | Cc: template-haskell(a)haskell.org; Simon Peyton-Jones | Subject: [Template-haskell] Bug? Unique class names... | | Hi, | I am trying to generate classes on the fly... as classes may get | generated more | than once, I want guaranteed unique names (sounds like a job for newName)... | However, whilst the first example works, the second fails: | | >-- this works | >test :: Q [Dec] | >test = do | > k <- newName "k" | > c <- classD (cxt []) (mkName "MyClass") [k] [] [] | > return [c] | | >-- this fails | >test :: Q [Dec] | >test = do | > n <- newName "MyClass" | > k <- newName "k" | > c <- classD (cxt []) n [k] [] [] | > return [c] | | In the second case this error is given: | | ghc-6.3: panic! (the `impossible' happened, GHC version 6.3): | nameModule MyClass{tc a3dX} | | Is this a bug? How easy is it to fix? | | Regards, | Keean. | | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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