Deriving regression or bad code?

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Ron Alford

8 Apr 2010 8 Apr '10

5:39 a.m.

I've attached the simplest example of my code that used to compile in GHC 6.10 now gives the error in GHC 6.12.1: baddata.hs:33:14: No instances for (Data Const, Data Var) arising from the 'deriving' clause of a data type declaration at baddata.hs:33:14-17 Possible fix: add an instance declaration for (Data Const, Data Var) or use a standalone 'deriving instance' declaration instead, so you can specify the instance context yourself When deriving the instance for (Data (Domain e g)) If I replace:

...

data Domain e g = Domain (Expr (Const :+: Var)) deriving (Data, Typeable)

with:

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data Domain e g = Domain (Expr (Const)) deriving (Data, Typeable)

then everything compiles. If nothing else, the error message is misleading. -Ron

Attachments:

baddata.hs (application/octet-stream — 1.0 KB)

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Ron Alford

8 Apr 8 Apr

2:35 p.m.

At Igloo's suggestion, it's now a ticket: http://hackage.haskell.org/trac/ghc/ticket/3965 -Ron On Thu, Apr 8, 2010 at 1:39 AM, Ron Alford wrote:

...

I've attached the simplest example of my code that used to compile in GHC 6.10 now gives the error in GHC 6.12.1: ...

Ron Alford

10 Apr 10 Apr

9:32 p.m.

Just for fun, I tried it on 6.12.1.20100330 with the same result. Does anyone have a workaround? Otherwise I need to revert to 6.10. -Ron On Thu, Apr 8, 2010 at 10:35 AM, Ron Alford wrote:

...

At Igloo's suggestion, it's now a ticket: http://hackage.haskell.org/trac/ghc/ticket/3965

-Ron

On Thu, Apr 8, 2010 at 1:39 AM, Ron Alford wrote:

...
I've attached the simplest example of my code that used to compile in GHC 6.10 now gives the error in GHC 6.12.1: ...

Simon Peyton-Jones

12 Apr 12 Apr

10:01 a.m.

It's really a bug. I've fixed it in my tree, but I'm at 2.8 and don't have time to validate etc. So I'm doubtful that I'll be in time to get a fix into 6.12.1, alas. Well, maybe I can build a patch and send it to Simon/Ian for testing. I'll try to do that if it's important to you. it's bit of an exotic case because of the higher-kindedness so I don't think it'll bite too man people There's a good workaround: use "standalone deriving". You | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell- | users-bounces@haskell.org] On Behalf Of Ron Alford | Sent: 10 April 2010 22:33 | To: glasgow-haskell-users | Subject: Re: Deriving regression or bad code? | | Just for fun, I tried it on 6.12.1.20100330 with the same result. | Does anyone have a workaround? Otherwise I need to revert to 6.10. | | -Ron | | On Thu, Apr 8, 2010 at 10:35 AM, Ron Alford wrote: | > At Igloo's suggestion, it's now a ticket: | > http://hackage.haskell.org/trac/ghc/ticket/3965 | > | > -Ron | > | > On Thu, Apr 8, 2010 at 1:39 AM, Ron Alford wrote: | >> I've attached the simplest example of my code that used to compile in | >> GHC 6.10 now gives the error in GHC 6.12.1: | > ... | > | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

Ron Alford

10:08 a.m.

I was getting a similar error with standalone deriving (already attached to that bug), but I didn't try it through-out. I'll let you know how it goes. -Ron On Mon, Apr 12, 2010 at 6:01 AM, Simon Peyton-Jones wrote:

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It's really a bug. I've fixed it in my tree, but I'm at 2.8 and don't have time to validate etc. So I'm doubtful that I'll be in time to get a fix into 6.12.1, alas.

Well, maybe I can build a patch and send it to Simon/Ian for testing. I'll try to do that if it's important to you.

it's bit of an exotic case because of the higher-kindedness so I don't think it'll bite too man people

There's a good workaround: use "standalone deriving".

You

| -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell- | users-bounces@haskell.org] On Behalf Of Ron Alford | Sent: 10 April 2010 22:33 | To: glasgow-haskell-users | Subject: Re: Deriving regression or bad code? | | Just for fun, I tried it on 6.12.1.20100330 with the same result. | Does anyone have a workaround? Otherwise I need to revert to 6.10. | | -Ron | | On Thu, Apr 8, 2010 at 10:35 AM, Ron Alford wrote: | > At Igloo's suggestion, it's now a ticket: | > http://hackage.haskell.org/trac/ghc/ticket/3965 | > | > -Ron | > | > On Thu, Apr 8, 2010 at 1:39 AM, Ron Alford wrote: | >> I've attached the simplest example of my code that used to compile in | >> GHC 6.10 now gives the error in GHC 6.12.1: | > ... | > | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

Simon Peyton-Jones

3:28 p.m.

The standalone deriving decl you need is the one for (Data (a :+: b)), not for Expr Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell- | users-bounces@haskell.org] On Behalf Of Ron Alford | Sent: 12 April 2010 11:09 | To: Simon Peyton-Jones | Cc: glasgow-haskell-users | Subject: Re: Deriving regression or bad code? | | I was getting a similar error with standalone deriving (already | attached to that bug), but I didn't try it through-out. I'll let you | know how it goes. | | -Ron | | | On Mon, Apr 12, 2010 at 6:01 AM, Simon Peyton-Jones | wrote: | > It's really a bug. I've fixed it in my tree, but I'm at 2.8 and don't have | time to validate etc. So I'm doubtful that I'll be in time to get a fix into | 6.12.1, alas. | > | > Well, maybe I can build a patch and send it to Simon/Ian for testing. I'll | try to do that if it's important to you. | > | > it's bit of an exotic case because of the higher-kindedness so I don't | think it'll bite too man people | > | > There's a good workaround: use "standalone deriving". | > | > You | > | > | -----Original Message----- | > | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell- | > | users-bounces@haskell.org] On Behalf Of Ron Alford | > | Sent: 10 April 2010 22:33 | > | To: glasgow-haskell-users | > | Subject: Re: Deriving regression or bad code? | > | | > | Just for fun, I tried it on 6.12.1.20100330 with the same result. | > | Does anyone have a workaround? Otherwise I need to revert to 6.10. | > | | > | -Ron | > | | > | On Thu, Apr 8, 2010 at 10:35 AM, Ron Alford wrote: | > | > At Igloo's suggestion, it's now a ticket: | > | > http://hackage.haskell.org/trac/ghc/ticket/3965 | > | > | > | > -Ron | > | > | > | > On Thu, Apr 8, 2010 at 1:39 AM, Ron Alford wrote: | > | >> I've attached the simplest example of my code that used to compile in | > | >> GHC 6.10 now gives the error in GHC 6.12.1: | > | > ... | > | > | > | _______________________________________________ | > | 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

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