March 2008 - Haskell-prime

Re: Some clarity please!
by Aaron Denney 23 Apr '08

23 Apr '08

On 2008-03-13, Ketil Malde <ketil(a)malde.org> wrote: > Aaron Denney <wnoise(a)ofb.net> writes: > >> Well, the way the report specifies that max's default definition >> is. I'd actually favor making that not an instance function at >> all, and instead have max and min be external functions. > > If you permit a naïve question: > > Prelude> :i Ord > class (Eq a) => Ord a where > compare :: a -> a -> Ordering > (<) :: a -> a -> Bool > (>=) :: a -> a -> Bool > (>) :: a -> a -> Bool > (<=) :: a -> a -> Bool > max :: a -> a -> a > min :: a -> a -> a > > ..while all functions could be easily derived from 'compare'. Or from > the Eq instance's (==) and (<), say. > > What is the reason for this? Efficiency? (Which couldn't be handled > equally well by RULES?) Otherwise, it looks like an invitation for > writing inconsistent instances. My impression (which may not be entirely accurate) is not primarily for efficiency (though that is one reason), but for ease of implementation. It may be easier in some cases to think through the various cases of compare, or to just figure out what (<=) is. Either of these is sufficient (perhaps in combination with (==) from the superclass). You can write things so that any of (<), (<=), (>), or (>=) are sufficient, but for writing the default compare, it's easiest to know ahead of time which you are basing it on, so definitions don't get circular. max and min seem to have neither justification going for them, although I suppose it's technically possible to write compare in terms of them and (==). I don't think GHC's RULES were around when Haskell 98 was being formalized, nor is it clear that one compiler's method should let other efficiency concerns go by the wayside. Of course, it would be nice to be able to write (==) in terms of compare. While doable manually there's no way to default it to that "smartly". There are similar issues with Functor and Monad. ISTR some discussion about this on the list previously. -- Aaron Denney -><-

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patch applied (haskell-prime-status): add overloaded string literals
by Simon Marlow 11 Apr '08

11 Apr '08

Mon Mar 31 15:31:44 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * add overloaded string literals M ./status.hs +2

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patch applied (haskell-prime-status): proposal: remove string gaps
by Simon Marlow 11 Apr '08

11 Apr '08

Mon Mar 31 15:26:03 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * proposal: remove string gaps M ./status.hs +2

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patch applied (haskell-prime-status): fix markup
by Simon Marlow 31 Mar '08

31 Mar '08

Mon Mar 31 11:41:36 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * fix markup M ./status.hs -1 +1

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patch applied (haskell-prime-status): add an entry for removing upper/lower case decision
by Simon Marlow 31 Mar '08

31 Mar '08

Mon Mar 31 11:40:34 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * add an entry for removing upper/lower case decision M ./status.hs +2

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patch applied (haskell-prime-status): remove duplicate: caseless underscore
by Simon Marlow 31 Mar '08

31 Mar '08

Mon Mar 31 11:39:35 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * remove duplicate: caseless underscore M ./status.hs -1

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patch applied (haskell-prime-status): add proposals from ExistingRecords
by Simon Marlow 31 Mar '08

31 Mar '08

Mon Mar 31 11:28:21 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * add proposals from ExistingRecords M ./status.hs +9

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patch applied (haskell-prime-status): accept the removal of n+k
by Simon Marlow 31 Mar '08

31 Mar '08

Thu Mar 27 14:25:49 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * accept the removal of n+k M ./status.hs -1 +1

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patch applied (haskell-prime-status): add entry for requiring spaces around dot
by Simon Marlow 31 Mar '08

31 Mar '08

Mon Mar 31 11:08:43 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * add entry for requiring spaces around dot M ./status.hs -1 +2

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patch applied (haskell-prime-status): wibble to MonomorphicPatternBindings entry
by Simon Marlow 27 Mar '08

27 Mar '08

Wed Mar 26 16:43:34 PDT 2008 Simon Marlow <simonmarhaskell(a)gmail.com> * wibble to MonomorphicPatternBindings entry M ./status.hs -1 +1

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