advanced class constraints in Haskell 98?
GHC accepts a class declaration like class Monad (m Maybe) => C m where ... without having any language extension switched on. But it isn't Haskell 98, is it? Hugs 2005 also accepts this.
On Thu, Jan 08, 2009 at 09:59:19PM +0100, Henning Thielemann wrote:
GHC accepts a class declaration like class Monad (m Maybe) => C m where ... without having any language extension switched on. But it isn't Haskell 98, is it? Hugs 2005 also accepts this.
Yes, it is. The Report is a good reference for questions like this.
On 8 Jan 2009, at 23:59, Henning Thielemann wrote:
GHC accepts a class declaration like class Monad (m Maybe) => C m where ... without having any language extension switched on. But it isn't Haskell 98, is it?
It is. From Report: ======================== A class assertion has form qtycls tyvar, and indicates the membership of the type tyvar in the class qtycls. A class identifier begins with an uppercase letter. A context consists of zero or more class assertions, and has the general form ( C1 u1, ..., Cn un ) where C1, ..., Cn are class identifiers, and each of the u1, ..., un is either a type variable, or the application of type variable to one or more types. ======================== "atype" is defined as ======================== atype -> gtycon | tyvar | ( type1 , ... , typek ) (tuple type, k>=2) | [ type ] (list type) | ( type ) (parenthesised constructor) ========================
Hugs 2005 also accepts this. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
On Fri, 9 Jan 2009, Miguel Mitrofanov wrote:
On 8 Jan 2009, at 23:59, Henning Thielemann wrote:
GHC accepts a class declaration like class Monad (m Maybe) => C m where ... without having any language extension switched on. But it isn't Haskell 98, is it?
It is.
From Report:
========================
A class assertion has form qtycls tyvar, and indicates the membership of the type tyvar in the class qtycls. A class identifier begins with an uppercase letter. A context consists of zero or more class assertions, and has the general form
( C1 u1, ..., Cn un )
where C1, ..., Cn are class identifiers, and each of the u1, ..., un is either a type variable, or the application of type variable to one or more types.
A nice. I jumped into 4.3 and found § § R 32 © ¦ 6 © ¦ 32 ¢ R ¨ © ¥ 7 ¤ ¢ ¨ 7 5© ¥ ¦ class => where ¢ § § § § ¥ ¦ ¡ 2 § 6 © R© 7
On Thu, 8 Jan 2009, Henning Thielemann wrote:
On Fri, 9 Jan 2009, Miguel Mitrofanov wrote:
On 8 Jan 2009, at 23:59, Henning Thielemann wrote:
GHC accepts a class declaration like class Monad (m Maybe) => C m where ... without having any language extension switched on. But it isn't Haskell 98, is it?
It is.
From Report:
========================
A class assertion has form qtycls tyvar, and indicates the membership of the type tyvar in the class qtycls. A class identifier begins with an uppercase letter. A context consists of zero or more class assertions, and has the general form
( C1 u1, ..., Cn un )
where C1, ..., Cn are class identifiers, and each of the u1, ..., un is either a type variable, or the application of type variable to one or more types.
A nice. I jumped into 4.3 and found
§ § R 32 ©
... copying from Haskell 98 report did not only insert rubbish, but also triggered sending the e-mail. I hope it did not more damage ... scontext -> simpleclass | (simpleclass_1, ..., simpleclass_n) simpleclass -> qtycls tyvar So it must be 'atype' instead of 'tyvar'? Haskell 98 is really mighty.
On Thu, Jan 08, 2009 at 10:27:59PM +0100, Henning Thielemann wrote:
A nice. I jumped into 4.3 and found
scontext -> simpleclass | (simpleclass_1, ..., simpleclass_n)
simpleclass -> qtycls tyvar
So it must be 'atype' instead of 'tyvar'? Haskell 98 is really mighty.
Oh. Don't I look silly? You were absolutely right, it's not Haskell 98. Actually Hugs does reject it without flags. Maybe you have a -98 stored somewhere?
On 9 Jan 2009, at 02:47, Ross Paterson wrote:
On Thu, Jan 08, 2009 at 10:27:59PM +0100, Henning Thielemann wrote:
A nice. I jumped into 4.3 and found
scontext -> simpleclass | (simpleclass_1, ..., simpleclass_n)
simpleclass -> qtycls tyvar
So it must be 'atype' instead of 'tyvar'? Haskell 98 is really mighty.
Oh. Don't I look silly? You were absolutely right, it's not Haskell 98.
Me too. I've looked at the type declaration syntax instead of instance declaration one.
Actually Hugs does reject it without flags. Maybe you have a -98 stored somewhere? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
On Fri, 9 Jan 2009, Miguel Mitrofanov wrote:
On 9 Jan 2009, at 02:47, Ross Paterson wrote:
On Thu, Jan 08, 2009 at 10:27:59PM +0100, Henning Thielemann wrote:
A nice. I jumped into 4.3 and found
scontext -> simpleclass | (simpleclass_1, ..., simpleclass_n)
simpleclass -> qtycls tyvar
So it must be 'atype' instead of 'tyvar'? Haskell 98 is really mighty.
Oh. Don't I look silly? You were absolutely right, it's not Haskell 98.
Me too. I've looked at the type declaration syntax instead of instance declaration one.
Maybe the report is not complete? I mean, the current behaviour of Hugs and GHC (as I observed it) is more consistent, and maybe that's what the designers had in mind.
Actually Hugs does reject it without flags. Maybe you have a -98 stored somewhere?
When starting, my Hugs tells Haskell 98 mode: Restart with command line option -98 to enable extensions
On Fri, Jan 09, 2009 at 01:11:12AM +0100, Henning Thielemann wrote:
Maybe the report is not complete? I mean, the current behaviour of Hugs and GHC (as I observed it) is more consistent, and maybe that's what the designers had in mind.
I'm puzzled by the Hugs behaviour. The current version rejects it, and I downloaded and built the Mar2005 version just to check, and it also rejected it, saying Illegal Haskell 98 class constraint in class declaration I think the GHC behaviour is connected with GHC's deferred context reduction, which also does not conform to Haskell 98.
On Fri, 9 Jan 2009, Ross Paterson wrote:
On Fri, Jan 09, 2009 at 01:11:12AM +0100, Henning Thielemann wrote:
Maybe the report is not complete? I mean, the current behaviour of Hugs and GHC (as I observed it) is more consistent, and maybe that's what the designers had in mind.
I'm puzzled by the Hugs behaviour. The current version rejects it, and I downloaded and built the Mar2005 version just to check, and it also rejected it, saying
Illegal Haskell 98 class constraint in class declaration
You are right. I don't know, what I made different before. Btw. 2005 was the copyright year, Hugs' version is September 2006: __ __ __ __ ____ ___ _________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-2005 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Bugs: http://hackage.haskell.org/trac/hugs || || Version: September 2006 _________________________________________ Haskell 98 mode: Restart with command line option -98 to enable extensions ERROR "src/Data/Spreadsheet/CharSource.hs":14 - Illegal Haskell 98 class constraint in class declaration *** Constraint : Monad (a Maybe) *** Context : (Monad (a Maybe), Monad (a Identity)) So, since GHC allows this extension without an option - how can I tell Cabal, which extension I'm using? Has it a name anyway?
Hi, Am Donnerstag, den 08.01.2009, 22:22 +0100 schrieb Henning Thielemann:
On 8 Jan 2009, at 23:59, Henning Thielemann wrote: From Report: A nice. I jumped into 4.3 and found
§ § R 32 © ¦ 6 © ¦ 32 ¢ R ¨ © ¥
7
¤ ¢ ¨ 7
5© ¥ ¦ class => where ¢
§ § § § ¥ ¦ ¡ 2 § 6 © R© 7
now how about this for a good argument that Haskell is just line noise. :-) Greetings, Joachim -- Joachim "nomeata" Breitner mail: mail@joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata@joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata@debian.org
participants (4)
-
Henning Thielemann -
Joachim Breitner -
Miguel Mitrofanov -
Ross Paterson