Re: Proposals and owners
On Thu, Aug 20, 2009 at 01:45:08PM +0100, Simon Marlow wrote: > On 08/08/2009 10:24, Ross Paterson wrote: > >On Sat, Aug 08, 2009 at 10:09:38AM +0100, Iavor Diatchki wrote: > >>I thought that the intended semantics was supposed to be that the only > >>element is bottom (hence the proposal to add a related empty case > >>construct)? > > > >If that were the case, a compiler could legitimately discard any value > >of such a type, because it could be easily reconstructed. I don't > >think that is what is intended. > > Just in case this question is still open: an empty data declaration > declares a type that has exactly zero constructors, not an abstract > type. What would it mean to define an abstract types? Haskell only > allows one definition of any given type. Yes, I take it back. Such types are typically used as phantom type arguments, e.g. the argument of Ptr, so the question I raised doesn't arise. ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
On 08/08/2009 10:24, Ross Paterson wrote: On Sat, Aug 08, 2009 at 10:09:38AM +0100, Iavor Diatchki wrote: I thought that the intended semantics was supposed to be that the only element is bottom (hence the proposal to add a related empty case construct)? If that were the case, a compiler could legitimately discard any value of such a type, because it could be easily reconstructed. I don't think that is what is intended. Just in case this question is still open: an empty data declaration declares a type that has exactly zero constructors, not an abstract type. What would it mean to define an abstract types? Haskell only allows one definition of any given type. Cheers, Simon ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
Ross Paterson wrote: On Sat, Aug 08, 2009 at 10:09:38AM +0100, Iavor Diatchki wrote: I thought that the intended semantics was supposed to be that the only element is bottom (hence the proposal to add a related empty case construct)? If that were the case, a compiler could legitimately discard any value of such a type, because it could be easily reconstructed. I don't think that is what is intended. Actually, I think it is. I think that's a natural consequence of the way Haskell is specified. GHC tries to pick the kind of bottom that you expected, but it doesn't always work really well, because it's not actually specified in any sort of formal way... Now, with imprecise exceptions, I'm not sure a compiler could legitimately discard the value. (by the way, for a type that you can unsafeCoerce anything to, GHC has a special type named "Any". Which is not the same as a data type with no constructors.) -Isaac ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
On Sat, Aug 08, 2009 at 10:09:38AM +0100, Iavor Diatchki wrote: > I thought that the intended semantics was supposed to be that the only > element is bottom (hence the proposal to add a related empty case > construct)? If that were the case, a compiler could legitimately discard any value of such a type, because it could be easily reconstructed. I don't think that is what is intended. ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
I thought that the intended semantics was supposed to be that the only element is bottom (hence the proposal to add a related empty case construct)? On Thu, Aug 6, 2009 at 3:49 PM, Ross Paterson wrote: > On Wed, Jul 29, 2009 at 02:34:26PM -0400, Stephanie Weirich wrote: >> Ok, I've put together a page on EmptyDataDecls: >> >> http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls > > I think this needs a sentence about semantics, to the effect that the > type is abstract. (Not that its only element is bottom.) > ___ > Haskell-prime mailing list > Haskell-prime@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-prime > ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
On Wed, Jul 29, 2009 at 02:34:26PM -0400, Stephanie Weirich wrote: > Ok, I've put together a page on EmptyDataDecls: > > http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls I think this needs a sentence about semantics, to the effect that the type is abstract. (Not that its only element is bottom.) ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
So is there a volunteer to flesh out the details of a proposal? On 31/07/2009 16:53, Iavor Diatchki wrote: +1. I completely agree. On Fri, Jul 31, 2009 at 6:04 PM, Lennart Augustsson wrote: I think that a natural extension to allowing empty data declarations would be to allow empty case expressions. On Wed, Jul 29, 2009 at 7:34 PM, Stephanie Weirich wrote: Ok, I've put together a page on EmptyDataDecls: http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls Cheers, Stephanie ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
On 02/08/2009 22:38, Niklas Broberg wrote:
I updated the code on the wiki page: the previous version didn't handle
prefix negation - did you implement that yourself in HLint?
No, I didn't implement prefix negation in HLint - it never came up as
an issue. Perhaps the underlying HSE library dealt with it for me -
Niklas would know.
In haskell-src-exts (and haskell-src, since that's inherited), unary
minus binds tighter than any infix operator:
exp0b :: { PExp }
: exp0b qop exp10b { InfixApp $1 $2 $3 }
| dvarexp { $1 }
| exp10b{ $1 }
exp10b :: { PExp }
: 'case' exp 'of' altslist { Case $2 $4 }
| '-' fexp { NegApp $2 }
| 'do' stmtlist { Do $2 }
| 'mdo' stmtlist{ MDo $2 }
| fexp { $1 }
It has never come up as a problem. Guess that's a point in case for
getting rid of unary minus as an operator. :-)
I think someone should propose this change for next year's Haskell
revision. We have evidence that (a) the current precedence of prefix
negation is confusing, and (b) it is rarely relied upon.
Changing the syntax as above is better IMO than the suggestion in
http://hackage.haskell.org/trac/haskell-prime/wiki/NegativeSyntax
to move prefix negation into the lexical syntax of numbers.
Cheers,
Simon
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Re: Proposals and owners
>> I updated the code on the wiki page: the previous version didn't handle
>> prefix negation - did you implement that yourself in HLint?
>
> No, I didn't implement prefix negation in HLint - it never came up as
> an issue. Perhaps the underlying HSE library dealt with it for me -
> Niklas would know.
In haskell-src-exts (and haskell-src, since that's inherited), unary
minus binds tighter than any infix operator:
> exp0b :: { PExp }
> : exp0b qop exp10b { InfixApp $1 $2 $3 }
> | dvarexp { $1 }
> | exp10b{ $1 }
> exp10b :: { PExp }
> : 'case' exp 'of' altslist { Case $2 $4 }
> | '-' fexp { NegApp $2 }
> | 'do' stmtlist { Do $2 }
> | 'mdo' stmtlist{ MDo $2 }
> | fexp { $1 }
It has never come up as a problem. Guess that's a point in case for
getting rid of unary minus as an operator. :-)
Cheers,
/Niklas
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Re: Proposals and owners
> remove FixityResolution from the context-free grammar >>> >>> http://hackage.haskell.org/trac/haskell-prime/wiki/FixityResolution >>> >>> Please take a look and comment. This fixes a nasty bug in the Haskell >>> syntax - albeit one that doesn't cause problems in practice, but still. >>> I >>> think the changes make the grammar look nicer, and help compiler >>> implementers by providing a sample implementation of fixity resolution. >>> >>> We better be sure the sample implementation is correct! I've tested it >>> fairly well, but I wouldn't rule out corner cases being wrong, especially >>> with prefix negation. >> >> The code in Resolve.hs has been used by HLint for months, and is the >> basis of the resolution used in haskell-src-exts 1.0.0. In that time I >> haven't seen any bugs with the fixity resolution. > > I updated the code on the wiki page: the previous version didn't handle > prefix negation - did you implement that yourself in HLint? No, I didn't implement prefix negation in HLint - it never came up as an issue. Perhaps the underlying HSE library dealt with it for me - Niklas would know. Thanks Neil ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
+1. I completely agree. On Fri, Jul 31, 2009 at 6:04 PM, Lennart Augustsson wrote: > I think that a natural extension to allowing empty data declarations > would be to allow empty case expressions. > > On Wed, Jul 29, 2009 at 7:34 PM, Stephanie > Weirich wrote: >> Ok, I've put together a page on EmptyDataDecls: >> >> http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls >> >> Cheers, >> Stephanie >> ___ >> Haskell-prime mailing list >> Haskell-prime@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-prime >> > ___ > Haskell-prime mailing list > Haskell-prime@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-prime > ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
I think that a natural extension to allowing empty data declarations would be to allow empty case expressions. On Wed, Jul 29, 2009 at 7:34 PM, Stephanie Weirich wrote: > Ok, I've put together a page on EmptyDataDecls: > > http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls > > Cheers, > Stephanie > ___ > Haskell-prime mailing list > Haskell-prime@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-prime > ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
On 31/07/2009 14:51, Neil Mitchell wrote: Hi > remove FixityResolution from the context-free grammar http://hackage.haskell.org/trac/haskell-prime/wiki/FixityResolution Please take a look and comment. This fixes a nasty bug in the Haskell syntax - albeit one that doesn't cause problems in practice, but still. I think the changes make the grammar look nicer, and help compiler implementers by providing a sample implementation of fixity resolution. We better be sure the sample implementation is correct! I've tested it fairly well, but I wouldn't rule out corner cases being wrong, especially with prefix negation. The code in Resolve.hs has been used by HLint for months, and is the basis of the resolution used in haskell-src-exts 1.0.0. In that time I haven't seen any bugs with the fixity resolution. I updated the code on the wiki page: the previous version didn't handle prefix negation - did you implement that yourself in HLint? Cheers, Simon ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
Hi >> > remove FixityResolution from the context-free grammar > > http://hackage.haskell.org/trac/haskell-prime/wiki/FixityResolution > > Please take a look and comment. This fixes a nasty bug in the Haskell > syntax - albeit one that doesn't cause problems in practice, but still. I > think the changes make the grammar look nicer, and help compiler > implementers by providing a sample implementation of fixity resolution. > > We better be sure the sample implementation is correct! I've tested it > fairly well, but I wouldn't rule out corner cases being wrong, especially > with prefix negation. The code in Resolve.hs has been used by HLint for months, and is the basis of the resolution used in haskell-src-exts 1.0.0. In that time I haven't seen any bugs with the fixity resolution. Thanks, Neil ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
I have fleshed out the report delta for > remove FixityResolution from the context-free grammar http://hackage.haskell.org/trac/haskell-prime/wiki/FixityResolution Please take a look and comment. This fixes a nasty bug in the Haskell syntax - albeit one that doesn't cause problems in practice, but still. I think the changes make the grammar look nicer, and help compiler implementers by providing a sample implementation of fixity resolution. We better be sure the sample implementation is correct! I've tested it fairly well, but I wouldn't rule out corner cases being wrong, especially with prefix negation. Cheers, Simon ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
empty decls Re: Proposals and owners
Stephanie Weirich wrote: > Ok, I've put together a page on EmptyDataDecls: > > http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls This reminds me to the related ticket: http://hackage.haskell.org/trac/ghc/ticket/393 If a dummy definition can be supplied for a function, then also a dummy constructor value can be supplied for a data type. If empty bindings and/or data types are supported the compiler can at least better warn about them. Cheers Christian ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
Ok, I've put together a page on EmptyDataDecls: http://hackage.haskell.org/trac/haskell-prime/wiki/EmptyDataDecls Cheers, Stephanie ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
I've had a go at #65 RelaxedDependencyAnalysis: http://hackage.haskell.org/trac/haskell-prime/wiki/RelaxedDependencyAnalysis ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
We still need owners for: On 08/07/2009 10:07, Simon Marlow wrote: > Remove n+k patterns > NonDecreasingIndentation Cheers, Simon ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Proposals and owners
On Wed, Jul 08, 2009 at 10:07:21AM +0100, Simon Marlow wrote: > As a reminder, here is the provisional list for 2010: > > > ForeignFunctionInterface > > LineCommentSyntax > > PatternGuards > > DoAndIfThenElse > > Remove n+k patterns > > RelaxedDependencyAnalysis > > EmptyDataDeclarations > > HierarchicalModules > > NonDecreasingIndentation > > remove FixityResolution from the context-free grammar > > change the syntax of QualifiedOperators > > These have already been done, so don't really need owners: > > > LineCommentSyntax > > DoAndIfThenElse > > PatternGuards > > I plan to take ownership of the following: > > > HierarchicalModules > > change the syntax of QualifiedOperators > > remove FixityResolution from the context-free grammar > > That leaves the following proposals needing owners: > > > ForeignFunctionInterface > > Remove n+k patterns > > RelaxedDependencyAnalysis > > EmptyDataDeclarations > > NonDecreasingIndentation > > Volunteers please! I'll volunteer for RelaxedDependencyAnalysis -- it's mostly done already. ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
