group keyword with TransformListComp

[Simon Peyton-Jones]

I agree it's undesirable.  It would be great if someone could lead a discussion leading to a better alternative.  Perhaps the same process that we use for libraries would be appropriate here. http://www.haskell.org/haskellwiki/Library_submissions  Namely: make a proposal, give an expiry date, lead discussion.  

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-users-
| bounces at haskell.org] On Behalf Of Neil Mitchell
| Sent: 29 June 2009 20:59
| To: Max Bolingbroke
| Cc: glasgow-haskell-users at haskell.org
| Subject: Re: group keyword with TransformListComp
| 
| Hi,
| 
| The question of syntax is always something that provokes intense
| discussion. My interest (and concern) with the choice of syntax in
| this case is three-fold:
| 
| 1) I want HLint to turn on as many Haskell extensions as possible when
| parsing, with the trade off that they don't break a massive number of
| existing programs. For each extension I have weighed up the number of
| programs that will get broken (because the extension steals previously
| valid syntax), vs the number that will be parsed (how popular the
| extension is). I've erred on the side of enabling extensions, so am
| happy to accept changes in meaning for a!b and $(a). Almost all
| extensions get turned on, with the exception of TransformListComp,
| which even breaks the source code to HLint itself - something no other
| extension does. It seems the syntax stolen is far too much, especially
| when compared to other extensions.
| 
| 2) I want to use TransformListComp in HLint. In particular, I have a
| nested pile of group/sort surrounding a list comp that would be
| perfect for TransformListComp. However, as it stands, I can't even
| enable the extension without that file breaking. I could qualify all
| the uses of group, but that seems too much hassle. I'd really like to
| enable the extension (without modification), and then start converting
| each group-like list-comp one at a time.
| 
| 3) We'll never be able to make TransformListComp enabled in future
| versions of Haskell' since we break too many programs. It's an
| extension that is destined forever to remain only an extension. That
| seems like a lonely life for an extension.
| 
| Thanks
| 
| Neil
| 
| On Sat, Jun 27, 2009 at 11:52 AM, Max Bolingbroke<omega.theta at gmail.com> wrote:
| > Hi,
| >
| > I agree this is annoying. It was hard to find syntax which was both
| > meaningful and currently unused, so we settled on this instead. As
| > Simon says, suggestions are welcome!
| >
| > Note that group *should* be parsed as a special id, so you can still
| > import D.L qualified and then use dot notation to access the function.
| >
| > Cheers,
| > Max
| >
| >
| > 2009/6/21 Neil Mitchell <ndmitchell at gmail.com>:
| >> Hi,
| >>
| >> The TransformListComp extension makes group a keyword. Unfortunately
| >> group is a useful function, and is even in Data.List. Thus,
| >> Data.List.group and TransformListComp are incompatible. This seems a
| >> very painful concession to give up a nice function name for a new
| >> extension. Is this intentional? Here's an example:
| >>
| >>> $ cat GroupKeyword.hs
| >>> {-# LANGUAGE TransformListComp #-}
| >>> module GroupKeyword where
| >>>
| >>> a = map head $ group $ sort [1..100]
| >>> $ ghci GroupKeyword.hs
| >>> GHCi, version 6.10.2: http://www.haskell.org/ghc/  :? for help
| >>> Loading package ghc-prim ... linking ... done.
| >>> Loading package integer ... linking ... done.
| >>> Loading package base ... linking ... done.
| >>> [1 of 1] Compiling GroupKeyword     ( GroupKeyword.hs, interpreted )
| >>>
| >>> GroupKeyword.hs:4:15: parse error on input `group'
| >>> Failed, modules loaded: none.
| >>> Prelude>
| >>
| >> There are some places I'd like to use TransformListComp, but I often
| >> want to use group in the same module.
| >>
| >> Thanks
| >>
| >> Neil
| >>
| >
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