October 2005 - Libraries

external core
by John Meacham 22 Mar '06

22 Mar '06

Now, the external core feature of ghc is great, but it is not utilized very much. The main reason I think is that there is a large barrier to entry in writing something that uses it since you need to parse/generate it. It would be nice if there were a standard library that came with ghc (or cabalized and portable even better) that could parse and pretty print external core. ideally, one could write a simple pass-through core processor that interacts with ghc in a single line and someone working on a new optimization need only worry about that. Also, it would make it very easy for jhc to generate and parse ghc core files (always an ulterior motive). I wanted to use jhcs front end to generate ghc core so I could get a true measure of the difference in just their back-end performance without taking into account ghc's superior high-level optimizations. In any case. I think all the code is out there in ghc and it just needs to be separated and cabalized. I know there was talk of creating a ghc internals library, but it would be nice if this code were portable and independent. John -- John Meacham - ⑆repetae.net⑆john⑈

3 4

Trie implementation
by Keith Wansbrough 10 Mar '06

10 Mar '06

Hi... I was writing some code yesterday to walk over a directory tree, and needed a Trie. Not seeing one around, I wrote a basic implementation of the functions I needed (attached below). Has anyone else done this? Should I polish it up and offer it for inclusion in Data? --KW 8-)

7 8

RFC: Time Library 0.2
by Ashley Yakeley 02 Nov '05

02 Nov '05

Just in time for HCAR... Please take a look at my second attempt at writing a replacement for the standard time library. http://semantic.org/TimeLib/ Take a look at the Haddock documentation: http://semantic.org/TimeLib/doc/html/ Download the source: http://semantic.org/TimeLib/TimeLib-0.2.tar.gz Or keep up-to-date: darcs get http://semantic.org/TimeLib/TimeLib/ It needs GHC 6.4.1. (I haven't tested with 6.4.) Just run "make" to build the library, tests and documentation. There's also a cabal file (as a completely separate build process), but I've been having trouble with that on Mac OS X. I'm particularly interested in comments from people who try to write little applications for it. What did you have trouble with? What made no sense? Also have a look at some use-cases, which get compiled as part of the package tests: http://semantic.org/TimeLib/TimeLib/test/UseCases.lhs Major changes since 0.1: * Moved to Data.Time, since the actual "System" part (getting the current time and time-zone) is relatively small. * Big simplification of types. Now tuples are used for calendar data (such as (year,month,day) for the Gregorian calendar), and the confusing DayEncoding class has been dropped. Some points: 1. There is no leap second table provided, though there is a type (LeapSecondTable) for such things. Any software compiled with a fixed table would soon become out of date. 2. There is no table of time-zones provided, since these also change. However, if there's a good way of getting this from the TZ database on the machine, I'll add that. It is actually possible to get the local time-zone for any given time, indeed one of the test programs finds your local summertime transitions. The Timezone type includes name, minutes of offset, and a "summertime" flag. 3. The TimeLocale type comes from the already existing System.Locale. 4. It's not possible to expunge POSIX time. Why? Because it's the only way to do sensible arithmetic on UTC times without knowing the leap second table and without worrying about one-second offsets. 5. I include Data.Fixed which provides a fixed-point arithmetic type (wrapper around Integer). It probably should be in a separate package. It allows dealing with seconds as a single thing, rather than as an integer/picoseconds pair. 6. I don't have any text-parsing functionality for times. This is a fair amount of work, so it would be good to know sensible requirements. 7. Time as measured by the CPU since system startup remains in System.CPUTime, which TimeLib does not intend to replace. -- Ashley Yakeley, Seattle WA

6 11

Data.IntMap/Set fixes and testsuite for collections.
by Jean-Philippe Bernardy 31 Oct '05

31 Oct '05

Hello folks, Could fptools maintainers apply the attached patch (or give me cvs access, at your convenience ;) which fixes Int* collections? Also, I've written a beginning of a testsuite for collections types. The basic idea is that test-code for multiple modules/types is generated from a signle haskell source by a simple pre-processing phase. This allows to circumvent the current lack of a class framework, and is also somewhat more flexible. Do you think this should be integrated to the ghc testsuite? (Does the preprocessing model fit it?) Cheers, JP.

1 0

Buglet in Data.IntSet.split and Data.IntSet.splitMember, patch included.
by Arthur van Leeuwen 30 Oct '05

30 Oct '05

Hello mailinglist-members, on the #haskell IRC channel Ketil Z. Malde noted that Data.IntSet.split failed on the case > let m = 1000000 in Data.IntSet.split (16*m) $ Data.IntSet.fromList $ map (*m) [17,18,19,30,40] so Bertram Felgenhauer (int-e(a)gmx.de) and I set out to fix that, noting along the way that Data.IntSet.splitMember was broken as well, and that negative numbers were not handled correctly either. The following patch fixes the problems: ----- 8< --- cut here --- >8 ----- --- IntSet.hs 2005-10-27 17:18:15.000000000 +0200 +++ FixedIntSet.hs 2005-10-27 17:59:49.000000000 +0200 @@ -35,7 +35,7 @@ -- (32 or 64). ------------------------------------------------------------------------ ----- -module Data.IntSet ( +module IntSet ( -- * Set type IntSet -- instance Eq,Show @@ -454,8 +454,23 @@ split x t = case t of Bin p m l r - | zero x m -> let (lt,gt) = split x l in (lt,union gt r) - | otherwise -> let (lt,gt) = split x r in (union l lt,gt) + | m < 0 -> if x >= 0 then let (lt,gt) = split' x l in (union r lt, gt) + else let (lt,gt) = split' x r in (lt, union gt l) + | otherwise -> split' x t + Tip y + | x>y -> (t,Nil) + | x<y -> (Nil,t) + | otherwise -> (Nil,Nil) + Nil -> (Nil, Nil) + +split' :: Int -> IntSet -> (IntSet,IntSet) +split' x t + = case t of + Bin p m l r + | match x p m -> if zero x m then let (lt,gt) = split' x l in (lt,union gt r) + else let (lt,gt) = split' x r in (union l lt,gt) + | otherwise -> if x < p then (Nil, t) + else (t, Nil) Tip y | x>y -> (t,Nil) | x<y -> (Nil,t) @@ -468,8 +483,23 @@ splitMember x t = case t of Bin p m l r - | zero x m -> let (lt,found,gt) = splitMember x l in (lt,found,union gt r) - | otherwise -> let (lt,found,gt) = splitMember x r in (union l lt,found,gt) + | m < 0 -> if x >= 0 then let (lt,found,gt) = splitMember' x l in (union r lt, found, gt) + else let (lt,found,gt) = splitMember' x r in (lt, found, union gt l) + | otherwise -> splitMember' x t + Tip y + | x>y -> (t,False,Nil) + | x<y -> (Nil,False,t) + | otherwise -> (Nil,True,Nil) + Nil -> (Nil,False,Nil) + +splitMember' :: Int -> IntSet -> (IntSet,Bool,IntSet) +splitMember' x t + = case t of + Bin p m l r + | match x p m -> if zero x m then let (lt,found,gt) = splitMember x l in (lt,found,union gt r) + else let (lt,found,gt) = splitMember x r in (union l lt,found,gt) + | otherwise -> if x < p then (Nil, False, t) + else (t, False, Nil) Tip y | x>y -> (t,False,Nil) | x<y -> (Nil,False,t) ----- 8< --- ereh tuc --- >8 ----- Hope this helps. :) Doei, Arthur. -- /\ / | arthurvl(a)cs.uu.nl | Work like you don't need the money /__\ / | A friend is someone with whom | Love like you have never been hurt / \/__ | you can dare to be yourself | Dance like there's nobody watching

2 1

cabal installation
by Frederik Eaton 30 Oct '05

30 Oct '05

It would be nice if cabal would unlink destination files before installing over them, rather than just calling "copyFile". It appears that when "copyFile" finds that a destination file already exists, rather than removing it, it tries to open and truncate it, which leads cabal to fail with the following error message when a new version of a running program is installed: *** Exception: bar: copyFile: resource busy (Text file busy) The commonly-used 'install' command does not suffer from this bug. Frederik

2 1

Data.Monoid
by Ross Paterson 27 Oct '05

27 Oct '05

(regurgitating http://www.haskell.org/pipermail/libraries/2005-July/004057.html) I propose to replace the instance instance Monoid (a -> a) where mempty = id mappend = (.) with newtype Endo a = Endo { runEndo :: a -> a } instance Monoid (Endo a) where mempty = Endo id Endo f `mappend` Endo g = Endo (f . g) instance Monoid b => Monoid (a -> b) where mempty _ = mempty mappend f g x = f x `mappend` g x

7 14

RE: [Haskell] Read Instances for Data.Map and Data.Set
by Simon Marlow 26 Oct '05

26 Oct '05

On 21 October 2005 08:43, Johannes Waldmann wrote: > Georg made the point that if a type is an instance of Show, > then it should also be an instance of Read, and read . show == id I rather think that this should be an explicit design requirement for Read/Show instances in the libraries, along with the requirement that the Show instance outputs valid Haskell syntax that can be included in a program (assuming appropriate imports, and possibly an appropriate type signature). Show is not for pretty-printing, it is for serialising. Are there any Show instances that violate these requirements in the base/haskell98 packages currently? Cheers, Simon

7 7

RE: [Haskell] Read Instances for Data.Map and Data.Set
by Simon Peyton-Jones 26 Oct '05

26 Oct '05

| > > There is no easy way currently for me to create a | > > short synonym for the defining module name. e.g. | > > | > > import Some.Very.Long.Module.Name as Local | > | > I'd prefer such self-imports if they wouldn't need so much effort. | | me too. I have requested it on the list before. they should be | straightforward to add, the recursive module namespace rules are not | very complicated at all and just allowing self-import doesn't involve | anything but tweaking the renamer a bit and a fast fixpoint iteration. If only it were so easy: module Foo where import Foo as Bar $(some splice stuff) We don't know what Foo exports until we've run all the splices. Sigh. Simon

1 0

RE: Data.* collections maintenance
by Simon Marlow 25 Oct '05

25 Oct '05

On 22 October 2005 11:58, Adrian Hey wrote: > One problem with AVL is the complexity of most of the code means > producing specialised unboxed implementations manually is not an > attractive proposition. Hopefully compilers will do this sort of > thing for us one day. > > But in reality I expect this sort of thing to be more of an issue > for benchmark style code using Ints. For more complex keys and > comparisons the indirection cost will be relatively insignificant > I think. For polymorpic implementations counting the actual number > of comparisons required by some function is just as important IMO. It's not just benchmark code - in GHC we use Int-based maps all over the place for speed. Given your promising results for polymorphic AVL trees, it's a fair bet that you could beat Data.IntMap with a specialised Int version. If you did, we would be forced to use Data.Tree.AVL in GHC :) Cheers, Simon

4 4