Re: ext-core Questions
On Fri, Dec 20, 2002 at 12:01:01PM -0500, [EMAIL PROTECTED] wrote: Secondly, in GHC produced Core programs, one sees frequently references to intermediate values from other Modules such as SystemziIO.lvl (print newline?) or GHCziNum.lvl1 (which seems to be an Integer constant) or even GHCziNum.a4 (which seems to be () :: Integer - Integer - Bool). The type of those names as well as any other names from imported Modules is not given, however. How then is it possible to type check a Core program? To typecheck a Core program, you need the type environment obtained from typechecking all the modules it imports -- i.e., at least the Prelude modules. The Core typechecker in the utils/ext-core directory in the GHC distribution gives an example. -- Kirsten Chevalier * [EMAIL PROTECTED] * Often in error, never in doubt ___ Glasgow-haskell-users mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: ANNOUNCE: Haskell Wiki resurrected
What do people feel about switching to a better Wiki implementation? I know we all have been secretly hoping a Wiki implemented in haskell would surface, but this is certainly an area which is already overcrowded and I think the community would be better served by a fully functional Wiki now. I highly recommend UseMod, http://www.usemod.com/cgi-bin/wiki.pl?UseModWiki It is very easy to set up and provides useful features like online browsing of Diffs and being much more robust than pywiki. On another note related to providing services to the haskell comunity, how about a public bugzilla server on bugs.haskell.org? (http://bugzilla.org) any haskell project which wishes to use the public bug server could be set up with an entry, it would be nice to have a central place to report bugs in the various haskell systems as well. This is not meant to replace whatever established project have, but rather provide a service to anyone with a haskell project who wishes bug reporting capability. Just some thoughts... John On Thu, Dec 05, 2002 at 10:36:15AM +, Keith Wansbrough wrote: Hi all... last night I resurrected the Haskell Wiki, http://haskell.org/wiki/wiki This is a set of web pages on Haskell which can be edited and updated by anyone. The intention is to accumulate the combined wisdom of posters to the Haskell lists - if you ever reply to a FAQ with what you think is a particularly good answer, please add it to the Wiki. If you see a FAQ that's been Frequently Asked, just point the poster at the appropriate page on the Wiki. Sadly, the Wiki isn't very stable at the moment. I'm hoping that one day it will be made more stable, but in the meantime, I've taken a snapshot of the state as it was last night, and placed a link to it on the haskell.org front page: http://haskell.org/wikisnapshot/FrontPage.html Note that no updates to the Wiki are ever lost; they're kept in a version control system. So if you see a blank page on the main Wiki where you once spent several hours writing the perfect page, don't worry - it's not lost! Hope this is useful to people! --KW 8-) PS: I'm not officially in charge of the Wiki, John Heron [EMAIL PROTECTED] is; I'm just helping him out at the moment. ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell -- --- John Meacham - California Institute of Technology, Alum. - [EMAIL PROTECTED] --- ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: ANNOUNCE: Haskell Wiki resurrected
--- John Meacham [EMAIL PROTECTED] wrote: On another note related to providing services to the haskell comunity, how about a public bugzilla server on bugs.haskell.org? (http://bugzilla.org) any haskell project which wishes to use the public bug server could be set up with an entry, it would be nice to have a central place to report bugs in the various haskell systems as well. This is not meant to replace whatever established project have, but rather provide a service to anyone with a haskell project who wishes bug reporting capability. I concur on this idea. This would be very useful. David J. Sankel ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Question About lists
Hello! I'm Working with Lists in Haskell, I´m a Beginner in Functional Programming and I would like to know if there isa way to write a more efficient function that return the length of a list, I wrote this one: long :: [a]-Intlong p = longitud p 0 where longitud [] s=s longitud (x:xs) s=longitud xs (s+1) but I think that it have a lineal grow O(n). thanks! Add photos to your e-mail with MSN 8. Get 3 months FREE*. ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Question About lists
Hi Cesar If you check the prelude, you will find the definition (something like): length::[a]-Int length= foldl' (\n _ - n + 1) 0 and the definition of foldl' foldl' :: (a - b - a) - a - [b] - a foldl' f a [] = a foldl' f a (x:xs) = (foldl' f $! f a x) xs Which also gives a linear complexity (O(n)) to length. Unless your representation of lists stores the length, you will pretty much always need linear time to find out the length as you have to count how many items there are. Alternatively, if getting the length is something you need to do a lot, consider creating your own datatype and corresponding class for inserts etc. that keeps the length on hand. This could allow O(1) length queries. On 30 Dec, Cesar Augusto Acosta Minoli wrote: htmldiv style='background-color:'DIV PHello! I'm Working with Lists in Haskell, I´m a Beginner in Functional Programming and I would like to know if there isnbsp;a way to write a more efficient function that return the length of a list, I wrote this one:/P Plongnbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp; ::nbsp; [a]-gt;IntBRlong pnbsp;nbsp;nbsp;nbsp; =nbsp; longitud p 0BRnbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp; whereBRnbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp; longitud []nbsp;nbsp;nbsp;nbsp;nbsp;nbsp; s=sBRnbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp; longitud (x:xs) s=longitud xs (s+1)/P Pbut I think that it have a lineal grow O(n)./P Pthanks!/P Pnbsp;/P Pnbsp;/P Pnbsp;/P Pnbsp;BRBR/P/DIV/divbr clear=allhrAdd photos to your e-mail with MSN 8. a href=http://g.msn.com/8HMEEN/2021;Get 3 months FREE*./a /html ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell -- Brett G. Giles Grad Student, University of Calgary Formal Methods, Category Theory, Semantics of Programming http://www.cpsc.ucalgary.ca/~gilesb mailto:[EMAIL PROTECTED] ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Question About lists
On Mon, 30 Dec 2002, Cesar Augusto Acosta Minoli wrote: Hello! I'm Working with Lists in Haskell, I´m a Beginner in Functional Programming and I would like to know if there is a way to write a more efficient function that return the length of a list, I wrote this one: long :: [a]-Int long p = longitud p 0 where longitud [] s=s longitud (x:xs) s=longitud xs (s+1) but I think that it have a lineal grow O(n). Yes, it's O(n), but you can't do any better for calculating the length of a list. Your second parameter seems to be an accumulator which is the sort of thing you'd make explicit in an imperative approach but can often be eliminated in functional code - e.g., long [] = 0 long (x:xs) = 1 + long xs A decent optimizing compiler will probably turn that code into something that uses an accumulator. This code probably isn't any more efficient than yours, it's just shorter. -- Mark ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Question About lists
Cesar Augusto Acosta Minoli wrote: Hello! I'm Working with Lists in Haskell, I´m a Beginner in Functional Programming and I would like to know if there is a way to write a more efficient function that return the length of a list, I wrote this one: long:: [a]-Int long p = longitud p 0 where longitud [] s=s longitud (x:xs) s=longitud xs (s+1) but I think that it have a lineal grow O(n). Sure. The only way to count the elements in a list is to, well, count the elements; it's an inherently linear operation. One suggestion, though is that you're working too hard; there's really no reason to define a locally defined function. The much simpler: long [] = 0 long (x:xs) = 1 + long xs will do quite nicely. HTH, --ag thanks! Add photos to your e-mail with MSN 8. Get 3 months FREE*. http://g.msn.com/8HMEEN/2021 ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell -- Artie Gold -- Austin, Texas ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Question About lists
On Mon, Dec 30, 2002 at 01:47:37PM -0600, Artie Gold wrote: One suggestion, though is that you're working too hard; there's really no reason to define a locally defined function. The much simpler: long [] = 0 long (x:xs) = 1 + long xs will do quite nicely. HTH, --ag There is already a length function in List and/or the Prelude. Bill ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
RE: Question About lists
long = sum . map (const 1) How's this? /JongKeun -Original Message- From: William Lee Irwin III [mailto:[EMAIL PROTECTED]] Sent: Tuesday, December 31, 2002 5:18 AM To: Artie Gold Cc: Cesar Augusto Acosta Minoli; [EMAIL PROTECTED] Subject: Re: Question About lists On Mon, Dec 30, 2002 at 01:47:37PM -0600, Artie Gold wrote: One suggestion, though is that you're working too hard; there's really no reason to define a locally defined function. The much simpler: long [] = 0 long (x:xs) = 1 + long xs will do quite nicely. HTH, --ag There is already a length function in List and/or the Prelude. Bill ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
