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Representing cyclic data structures efficiently in Haskell
by Sarah Thompson 08 Jul '03

08 Jul '03

What is the best way to represent cyclic data structures in Haskell? Lists are trivial. Trees are trivial. But what if the thing you're trying to represent is shaped like an electronic circuit, with a (possibly large) number of nodes connected by multiple arrows to other nodes? In an imperative language like C++, I'd probably just model the circuit directly, with objects representing nodes and pointers representing links between nodes. A good way to model this in Haskell is less obvious, however. A simplistic approach would be to represent such a structure as a list of nodes, where each node contained a list of other connected nodes. Containing the actual nodes within the sub-lists probably isn't feasible -- some kind of reference would be necessary in order to get around chicken-and-egg problems with instantiating the data structure. But, in this case, it's not so easy to see how one could 'walk' the structure efficiently, because moving from node to node would involve quite horrible (possibly slow) lookups. In C++, I'd simply follow a pointer, which would be an extremely fast operation. I would also need to implement efficient indexes into the data structure -- flat searching will be too slow for non-trivial amounts of data. In C++, I'd implement one or more external (probably STL-based) indexes that point into the main data structure. How do people typically solve this problem at the moment? I know a few people out there have written hardware compilers in Haskell and similar languages, so there should be some experience of this in the community. I can probably work something out soon enough, but reinventing the wheel is never a great idea. Thank you in advance, -- ---------------------------------------------- / __ + / Sarah Thompson **** / / (_ _ _ _ |_ / * / / __)(_|| (_|| ) / sarah(a)telergy.com * / / + / http://findatlantis.com/ / ----------------------------------------------

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RE: Representing cyclic data structures efficiently in Haskell
by Hal Daume 07 Jul '03

07 Jul '03

>From reading your message, it seems you want a graph library of sorts. I've used FGL extensively and found it to be very nice. It even provides both a purely functional interface as well as an imperative-esque interface. It also comes with a bunch of standard algorithms built in, though I don't know enough about circuitry stuff to know whether those would be useful or not. If FGL seems like overkill to you, I have my own little mini graph library which basically looks like: - An ADT, Node: newtype Node = Node Int deriving ... - The 'Graph n e' data structure, containing: - a FiniteMap from n -> Node - an (growable?) array of type IOArray (Node,Node) e the array represents the edges in the top half (i do some index fiddling to get this efficient) and the finitemap represents the node labellings. It's a pretty stupid interface and works a lot better when the graphs are fixed size (that way you don't need to grow the array). But it works. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-cafe-admin(a)haskell.org > [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Sarah Thompson > Sent: Monday, July 07, 2003 8:04 AM > To: haskell-cafe(a)haskell.org > Subject: Representing cyclic data structures efficiently in Haskell > > > What is the best way to represent cyclic data structures in Haskell? > > Lists are trivial. Trees are trivial. But what if the thing you're > trying to represent is shaped like an electronic circuit, with a > (possibly large) number of nodes connected by multiple arrows > to other > nodes? In an imperative language like C++, I'd probably just > model the > circuit directly, with objects representing nodes and pointers > representing links between nodes. A good way to model this in > Haskell is > less obvious, however. > > A simplistic approach would be to represent such a structure > as a list > of nodes, where each node contained a list of other connected nodes. > Containing the actual nodes within the sub-lists probably > isn't feasible > -- some kind of reference would be necessary in order to get around > chicken-and-egg problems with instantiating the data > structure. But, in > this case, it's not so easy to see how one could 'walk' the structure > efficiently, because moving from node to node would involve quite > horrible (possibly slow) lookups. In C++, I'd simply follow a > pointer, > which would be an extremely fast operation. > > I would also need to implement efficient indexes into the > data structure > -- flat searching will be too slow for non-trivial amounts of > data. In > C++, I'd implement one or more external (probably STL-based) indexes > that point into the main data structure. > > How do people typically solve this problem at the moment? I > know a few > people out there have written hardware compilers in Haskell > and similar > languages, so there should be some experience of this in the > community. > I can probably work something out soon enough, but > reinventing the wheel > is never a great idea. > > Thank you in advance, > > -- > ---------------------------------------------- > / __ + / Sarah Thompson **** / > / (_ _ _ _ |_ / * / > / __)(_|| (_|| ) / sarah(a)telergy.com * / > / + / http://findatlantis.com/ / > ---------------------------------------------- > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Mailing Lists - Fax Directory - Company Databases
by Peter Cororan 06 Jul '03

06 Jul '03

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ucuz arama
by NETTEALO 06 Jul '03

06 Jul '03

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Worldwide Partners program
by The TechNews 05 Jul '03

05 Jul '03

The TechNews, July 2003 Production Mini-plants in mobile containers. Worldwide Partners program Science Network will supply to countries and developing regions the technology and necessary support for production in series of Mini-plants in mobile containers (40-foot). The Mini-plant system is designed in such a way that all the production machinery is fixed on the platform of the container, with all wiring, piping, and installation parts; that is, they are fully equipped... and the mini-plant is ready for production." More than 700 portable production systems: Bakeries, Water purification, Dehydrated food, Steel Nails, Fruit juice preparation, Tire Retreading, Reinforcement Bar Bending for Construction Framework, Sheeting for Roofing, Ceilings and Façades, Plated Drums, Aluminum Buckets, Injected Polypropylene Housewares, Pressed Melamine Items (Glasses, Cups, Plates, Mugs, etc.), Mufflers, Construction Electrically Welded Mesh, Plastic Bags and Packaging, Mobile units of medical assistance, Sanitary Material, Hypodermic Syringes, Hemostatic Clamps, etc. Science Network has started a Co-investment program for the installation of small Assembly plants to manufacture in series the Mini-plants of portable production on site, region or country where required. One of the most relevant features is the fact that these plants will be connected to the World Trade System (WTS) with access to more than 50 million raw materials, products and services and automatic transactions for world trade. Due to financial reasons, involving cost and social impact, the best solution is setting up assembly plants on the same countries and regions, using local resources (labor, some equipment, etc.) Science Network participates at 50% (fifty percent) for investment of each Assembly plant. If you are interested in being a Science Network partner in your country or region, you can send your CV to: Mini-plants <A HREF="mailto:letters@the-tech-news.com">Worldwide Partners program</A> By Robert B. Lethe, The TechNews, Editor ------------------------------------------------------------------------- If you received this in error or would like to be removed from our list, please return us indicating: remove or un-subscribe in subject field, Thanks. <A HREF="mailto:editor@the-tech-news.com"> Editor</A> © 2003 The TechNews. All rights reserved.

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FFI Ptr question
by paul＠theV.net 03 Jul '03

03 Jul '03

If a C function returns a (void*), let's say: data MyObj = MyObj foreign import ccall "static myobj_ffi.h new_obj" newMyObject :: IO (Ptr MyObj) ptr <- newMyObject should I free the ptr afterwards or not? If I have another imported C function: foreign import ccall "static myobj_ffi.h print_obj" printMyObject :: Ptr MyObj -> IO () Can I safely assume the C function print_obj(void *) always get the same pointer even if I call (printMyObject ptr) multiple times? Any hints is greatly appreciated! Regards, .paul.

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by webmaster 03 Jul '03

03 Jul '03

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RE: haskell array access
by Simon Peyton-Jones 01 Jul '03

01 Jul '03

| Are there any concoctions of flags/pragmas/techniques to coax GHC into | unrolling a function (or rather an IO computation in this case) a couple | of iterations. There was another (admittedly also noddy) program that I | could get to near gcc, but only by unrolling by hand (though Ian's TH | stuff likely could have done it). GHC generally doesn't unroll recursions. The inliner runs repeatedly, so it's hard for it to know how much it unrolled "last time". (There's a paper "Secrets of the GHC inliner" on my publications page.) Simon

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UML diagrams of Haskell
by Bas van Dijk 30 Jun '03

30 Jun '03

Hi, It's maybe a weird question but do there exist UML diagrams of the Haskell language. They don't necessarily have to be UML diagrams, as long as they show the different concepts in the language (i.e.: functions, datatypes, patterns, etc.) and the relations between them(i.e.: a function consists of other functions, functions have a type). Bas.

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RE: Arrow Classes
by Simon Peyton-Jones 30 Jun '03

30 Jun '03

It may interest you guys to know that Ross Paterson and I have just put syntactic support for arrows into GHC. It's only in the CVS version at the moment, and is not documented at all, but those things will come. The type error messages should, I hope, be a lot better than those one can get by type checking pre-processed code. Simon | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Joe | English | Sent: 28 June 2003 17:01 | To: haskell-cafe(a)haskell.org | Subject: Re: Arrow Classes | | | Ashley Yakeley wrote: | > Wolfgang Jeltsch wrote: | > | > > This brings me to another point. One year ago we had a discussion on The | > > Haskell Mailing List concerning arrows. (The subject of the mails was just | > > "arrows".) The point was that it seemed strange to me that first and second | > > are included in the basic arrow class Arrow while left and right have their | > > extra class ArrowChoice. Not only that it seemed strange to me but it made | > > impossible to make Parser baseMonad an instance of Arrow. Parser baseMonad | > > has nice implementations of pure and (>>>) but none of first or second. | > | > I agree. My own Arrow module hierarchy looks more or less like this: | > | > class Compositor comp where [...] | > class (Compositor arrow) => Arrow arrow where [...] | > class (Arrow arrow) => ProductArrow arrow where [...] | > class (Arrow arrow) => CoproductArrow arrow where [...] | > class (ProductArrow arrow,CoproductArrow arrow) => FullArrow arrow | > instance (ProductArrow arrow,CoproductArrow arrow) => FullArrow arrow | > class (Arrow arrow) => ArrowFix arrow where [...] | > class (FullArrow arrow) => ApplyArrow arrow where [...] | | | On that topic, see below for what mine looks like | (from HXML, <URL: http://www.flightlab.com/~joe/hxml/ >). | | I started off with Hughes' conventions, but for some | reason could never remember the difference between &&& and ***, | or between ||| and +++. I found &&&, >&<, |||, >|< to have | better mnemonic value. This also frees up +++ for ArrowPlus, | which -- in HXML applications -- is frequently used and should | thus be easy to type. | | When using the ArrowChoice operators, I kept tripping over all | the 'Either' coproduct types, so added some syntactic sugar | (borrowed from HaXML): | | data Choice a = a :> a | class (Arrow a) => ArrowChoice a where | [ ... ] | ( ?>) :: (b -> Bool) -> Choice (a b c) -> a b c | (>?>) :: a b Bool -> Choice (a b c) -> a b c | | I found "p ?> f :> g" much more pleasant to use. | | (I also like the idea of splitting the product operators out of | the base Arrow class -- will consider doing that in my library). | | -- | | infixr 5 +++ | infixr 3 >&<, &&& | infixr 2 >|<, |||, ?>, >?>, :> | infixl 1 >>> | | class Arrow a where | arr :: (b -> c) -> a b c | (>>>) :: a b c -> a c d -> a b d | apfst :: a b c -> a (b,x) (c,x) | apsnd :: a b c -> a (x,b) (x,c) | (>&<) :: a b c -> a d e -> a (b,d) (c,e) | (&&&) :: a b c -> a b d -> a b (c,d) | liftA2 :: (b -> c -> d) -> a e b -> a e c -> a e d | aConst :: c -> a b c | idArrow :: a b b | -- Minimal implementation: arr, >>>, apfst or >&< | | data Choice a = a :> a | class (Arrow a) => ArrowChoice a where | apl :: a b c -> a (Either b d) (Either c d) | apr :: a b c -> a (Either d b) (Either d c) | (>|<) :: a b c -> a d e -> a (Either b d) (Either c e) | (|||) :: a b c -> a d c -> a (Either b d) c | ( ?>) :: (b -> Bool) -> Choice (a b c) -> a b c | (>?>) :: a b Bool -> Choice (a b c) -> a b c | -- Minimal implementation: >|< or apl | | class (Arrow a) => ArrowApply a where | app :: a (a b c,b) c | | class (Arrow a) => ArrowZero a where | aZero :: a b c | aMaybe :: a (Maybe c) c | aGuard :: (b -> Bool) -> a b b | | class (Arrow a) => ArrowPlus a where | (+++) :: a b c -> a b c -> a b c | | | | --Joe English | | jenglish(a)flightlab.com | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: UML diagrams of Haskell
by Hal Daume 30 Jun '03

30 Jun '03

There's something like UML, called FAD (Functional Analysis and Design, I believe). It was the topic of Daniel Russell's PhD thesis. See http://www.cs.kent.ac.uk/pubs/2001/1152/index.html for more. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-cafe-admin(a)haskell.org > [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Bas van Dijk > Sent: Sunday, June 29, 2003 2:50 PM > To: HaskellCafe Mailinglist > Subject: UML diagrams of Haskell > > > Hi, > > It's maybe a weird question but do there exist UML diagrams > of the Haskell > language. > They don't necessarily have to be UML diagrams, as long as > they show the > different concepts in the language (i.e.: functions, > datatypes, patterns, > etc.) and the relations between them(i.e.: a function > consists of other > functions, functions have a type). > > Bas. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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RE: Simple monads
by Hal Daume 29 Jun '03

29 Jun '03

> (a) People could point out to me where I'm still confused, as > revealed by > my code. Is it needlessly complicated? looks pretty reasonable to me :) as to why Unique is in the IO monad is probabyl because if it were in any other monad, you could start the monad twice and thus get a repeat of each ID (if that makes sense). The only way around this is to put it in IO.

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Bom dia haskell-cafe
by Marta 29 Jun '03

29 Jun '03

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Template Haskell question
by Ashley Yakeley 28 Jun '03

28 Jun '03

Can anyone tell me what's wrong with this? -- ghc -fglasgow-exts -c TH.hs module TH where { import Language.Haskell.THSyntax; class HasZero a where { zero :: a; }; aninstance :: TypQ -> Q [Dec]; aninstance t = [d| instance HasZero $t where -- error here { zero = 0; }; |]; $(aninstance [t|Int|]) $(aninstance [t|Integer|]) } $ ghc -fglasgow-exts -c TH.hs TH.hs:14: Malformed context in instance header All I want to do is spin off a number instances for a number of types... -- Ashley Yakeley, Seattle WA

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RE: haskell array access
by Hal Daume 27 Jun '03

27 Jun '03

> At best case for Haskell, 15.5 times slower. The thing about > bounds checking, > in Haskell it's always there. In C, you might have it, you > might not there is > no certainty by the language, only by design and > implementation. So with C, > one is free to live dangerously. If you're using GHC, there's Data.Array.Base.unsafeAt which is the one which doesn't do bounds checking.

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RE: Help with ghci and Yet Another Haskell Tutorial
by Hal Daume 27 Jun '03

27 Jun '03

toUpper is in the Char (or Data.Char) library. You can do: Prelude> :m Data.Char Data.Char> map toUpper "hello world" or specify it completely. Prelude> map Data.Char.toUpper "hello world" I'll fix this reference in YAHT. I believe that Hugs automatically exports toUpper, which is why it was in there to begin with. - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume -----Original Message----- From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Mark Espinoza Sent: Friday, June 27, 2003 7:53 AM To: haskell-cafe(a)haskell.org Subject: Help with ghci and Yet Another Haskell Tutorial Greetings, I am going through the Tutorial using ghc on a redhat 8.0 system. Everything works fine untill I get to the map function: Prelude> map toUpper "hello world" <interactive>:1: Variable not in scope: `toUpper' Prelude> Can anyone tel me what is or might be going on? Thanks. Sincerely, Mark Get your free e-mail address at http://felinemail.zzn.com ___________________________________________________________ Get your own Web-based E-mail Service at http://www.zzn.com _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Help with ghci and Yet Another Haskell Tutorial
by Mark Espinoza 27 Jun '03

27 Jun '03

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ELearnChina Conference 2003 - Only 4 Weeks To Go!
by Edwin Jones 27 Jun '03

27 Jun '03

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RE: haskell array access
by Simon Peyton-Jones 27 Jun '03

27 Jun '03

Several comments 1. In Haskell "mod" is a lot more expensive than "rem", because it involves careful jiggery pokery with the sign of the result. That's why your boxed version was slower (nothing to do with boxing). 2. GHC does indeed optimise away the array access if you aren't careful, and does in Derek's code. Below is a version that avoids doing so, in the same way as the C version, by returning one of the values. 3. Derek correctly points out that gcc does not do array-bound checks. GHC should eliminate them, but it's a non-trivial analysis and GHC does not currently attempt it. You can always use unsafeAt, as Derek does. 4. The UArray stuff builds an array of unboxed Ints, like C. If you use ordinary boxed arrays, the loop has to unbox the Int every time around the loop, which makes it slower (2.6s) With that done, we get ghc -O2 -fliberate-case-threshold20 1.8s gcc -O2 1.4s Seems close enough to me; have not investigated further. The "liberate-case" thing is a practically-undocumented GHC optimisation that switches on with -O2. It specialises a loop that unboxes a free variable (here the array k) so that the unboxing doesn't happen each time round the loop. The threshold at which GHC thinks there is too much code dup is set very low by default, so the flag increases it. Simon ====================== k :: UArray Int Int k = array (0,15) [(i, i+1) | i <- [0 .. 15] ] acc :: Int -> Int -> Int acc r 0 = r acc r n = r `seq` acc (k `unsafeAt` (n `rem` 16)) (n - 1) main :: IO () main = print (acc 0 100000000) ====================== | Anyways, | int main(void){ | int i, k; | int a [16]; | for (i=0; i<=100000000; i++) { | k = a [i % 16]; | } | printf("%d\n",k); | return 0; | } | compiled with MinGW 3.2 -O/-O2/-O3 runs in 1.8s using time. | | int main(void){ | int i, k; | int a [16]; | for (i=0; i<=100000000; i++) { | k = a [i % 16]; | } | printf("%d\n",k); | return 0; | } | | The following (compiled with -O2 -fglasgow-exts and GHC 6.1 i.e. a CVS | version) beats the C version taking only .8s. They don't do the same | thing (the Haskell version "does" more, but prints something different). | Looking at the core/stg/c/asm (the asm and C was quite messy compared | with other times), it certainly doesn't appear to be optimizing this to | print 0, and it does appear (though I'm less sure here) to be doing | everything as it should, but it's really hard to read the assembly, | since we don't use the value we lookup I can easily see gcc dropping it | altogether, though the C GHC spits out is pretty unusual for gcc, so it | may not. | | module Main (main) where | import Data.Array.Unboxed (UArray, array) | import Data.Array.Base (unsafeAt) -- if C doesn't, why should we? | import GHC.Exts | | k :: UArray Int Int | k = array (0,15) [(i, i+1) | i <- [0 .. 15] ] | | acc :: Int# -> Int# | acc 0# = 0# | acc n = (k `unsafeAt` (I# (n `remInt#` 16#))) `seq` acc (n -# 1#) | | main :: IO () | main = print (I# (acc 100000000#)) | | However, I'm am somewhat surprised that I seemingly had to unbox by hand | to get quite close (in fact, better) than C. I expected the following | version to be comparable to the C version (and it is orders of magnitude | faster than the original version which was over 5min when I killed it | (though I think I compiled it with just -O), this version taking 14s). | | module Main (main) where | import Data.Array.Unboxed (UArray, array) | import Data.Array.Base (unsafeAt) -- if C doesn't, why should we? | | k :: UArray Int Int | k = array (0,15) [(i, i+1) | i <- [0 .. 15] ] | | acc :: Int -> Int | acc 0 = 0 | acc n = (k `unsafeAt` (n `mod` 16)) `seq` acc (n - 1) | | main :: IO () | main = print (acc 100000000) | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: haskell array access
by Hal Daume 27 Jun '03

27 Jun '03

This has been hinted to before: gcc gets rid of the loop. bash-2.05b$ gcc -O3 arr.c -S -o arr.s bash-2.05b$ cat arr.s .file "arr.c" .def ___main; .scl 2; .type 32; .endef .text .align 2 .align 16 .globl _main .def _main; .scl 2; .type 32; .endef _main: pushl %ebp movl %esp, %ebp subl $72, %esp xorl %eax, %eax andl $-16, %esp call __alloca call ___main xorl %eax, %eax .align 16 L7: incl %eax cmpl $100000000, %eax jle L7 leave ret the inside of the loop is exactly: L7: incl %eax cmpl $100000000, %eax jle L7 which doesn't read the array! essentially you are being unfare to ghc by making it seq the array element, but not doing the same to GCC. even with -O0, gcc gets rid of the loop body. one solution: add in the assembly to actually read the array (i'm too lazy and busy to do this). - hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-cafe-admin(a)haskell.org > [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Lex Stein > Sent: Thursday, June 26, 2003 3:46 PM > To: Sven Panne > Cc: haskell-cafe(a)haskell.org > Subject: Re: haskell array access > > > > Great, thanks. Those suggestions narrow the gap from GHC -O being 330x > slower than GCC -O3 to it being 20x slower. Here are the new results: > > gcc -O3 0.54s > ocamlopt 1.11s > ghc -O 10.76s > ocamlc 14.10s > > GHC is still pretty slow for native x86 instruction code. Is > there any way > to further explain the performance gap ? (new code below) > > Thanks! > Lex > > Haskell (GHC) source: > > import Array > k :: Array Int Int > k = Array.array (0,15) [(i, i+1) | i <- [0 .. 15] ] > acc :: Int -> Int > acc 0 = 0 > acc n = seq (k Array.! (n `mod` 16)) (acc (n-1)) > main = do > print (acc 100000000) > > Caml test source: > > let a = Array.make 16 0;; > let rec do1 i z = > if (i>100000000) then z else > do1 (i+1) (z + a.(i mod 16));; > do1 0 0;; > > C (gcc) test source: > > int main () { > int i, k = 0; > int a [16]; > for (i=0; i<100000000; i++) { > k += a [i % 16]; > } > return (k); > } > > > On Fri, 27 Jun 2003, Sven Panne wrote: > > > Well, part of the answer is definitely that the Haskell > program is the > > *only* one which really uses the array elements. :-) I > guess that the > > compilers for the other languages simply remove the array > access from > > the generated code (gcc definitely does, only an empty loop > remains). > > > > Another reason is that the type signatures are missing, so > Integer is > > used instead of Int, which is a bit unfair. Adding > > > > k :: Array Int Int > > acc :: Int -> Int > > > > cuts down the time by more than factor 5 on my machine. > > > > Cheers, > > S. > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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"callbacks" in Haskell
by Robert Vollmert 26 Jun '03

26 Jun '03

Hello, I've been having a little trouble writing a module that waits for and handles IO events, e.g. by reading from a pipe. It seemed natural to use some form of callbacks here, though that may very well be the wrong approach. I'd be happy to hear of alternatives. Anyway, I got a callback-based approach to work to some extent, but am not happy with the callback's type. The abstract form of this module is as follows. I'd appreciate any input. A class that specifies what we expect of the base monad. > class (Monad m) => MonadReq m A class that specifies what we provide to the callback. > class (Monad m) => MonadProv m The module's main function. > f :: (MonadReq m) => Callback m a -> m a > f c = ... Internally, we wrap the base monad with some monad transformer, say > data InternalT m a = ... with > instance MonadTrans InternalT so that the callback can access the base monad, and > instance (MonadReq m) => MonadProv (InternalT m) so that we can actually provide MonadProv. A type for callback that works is > type Callback m a = InternalT m a What I don't like about this is that we shouldn't really need to expose what exact monad transformer we use. Also, if we added a second function that also runs the callback in a MonadProv but that uses a different transformer (for instance, needing to keep track of some extra state), we'd need a new callback type. What seems to be the right type is > type Callback m a = forall t. (MonadTrans t, MonadProv (t m)) => t m a which sort of works with '-fglasgow-exts' (what's this extension called?). However, it seems to cause all kinds of problems, e.g. pairs of this type appear to be illegal. Cheers Robert

2 2

Re: MacOS X Project Builder and Haskell
by Ashley Yakeley 26 Jun '03

26 Jun '03

At 2003-06-25 11:51, Andre Pang wrote: >Hi Ashley, I guess you've heard of the announcements of the new Apple >IDE announced at WWDC recently ("Xcode"). I'm at WWDC right now, and >I'll do my best to talk to the Apple engineers there to make sure that >all the infrastructure is in place to be able to integrate Haskell/GHC >with Xcode. Xcode does look a little bit more extensible than Project >Builder, but since it's in beta, not everything is actually >documented/integrated yet (in particular, its native build system). The (reduced) screen-shots of Xcode on the Apple site are so pretty I was worrying whether it would actually be as powerful as PB, which I'm fairly impressed with. I'm delighted to hear that Xcode will be even more extensible. >However, if you still want to use Project Builder, I have managed to >get GHC integration going. It's not pretty (put it this way: Perl is >involved ...), but it _does_ work. I'm planning to release it in ~2 >weeks, but if you can't wait, email me back and I'll give you a preview >if I have time :). All my Haskell development is cross-platform at the moment, so I must use makefiles and thus "legacy" targets anyway. Though I'm sure I'll have a look at it when you've finished with it... Actually my biggest build problem at the moment is that the version of make that comes with the system is buggy. I use the make that comes with fink, but of course not everyone has that installed. Perhaps this will be fixed in the new Darwin. -- Ashley Yakeley, Seattle WA Almost empty page: <http://semantic.org/>

1 0

MacOS X Project Builder and Haskell
by Ashley Yakeley 25 Jun '03

25 Jun '03

Does anyone else use Project Builder with Haskell? Once you fiddle around with it a bit, it seems to work OK with makefiles. But I wondered if anyone had any Haskell-specific extensions? -- Ashley Yakeley, Seattle WA

2 2

Shoot self in foot
by Shawn P. Garbett 25 Jun '03

25 Jun '03

Based on the earlier posted joke on this list, I put together the following code. Could probably use a bit of simplification, but you get the picture. import IO import GHC.IOBase -- True = nice foot, False = shot up by some lunatic type Foot = Bool -- Manage a request from the user, given request and current foot state manage :: Char -> Foot -> IO Foot manage c foot -- InterleaveIO Makes the request "lazy" | c == '1' = unsafeInterleaveIO $ do putStr "OUCH!!!! Shoot Self in Foot\n" return False -- The foot is now shot -- The doctor examines the state of the foot variable | c == '2' = do putStr "Doctor examines foot\n" if foot then putStr "I have a good foot.\n" else putStr "I have a shot-up foot.\n" return foot -- Otherwise just keep processing | otherwise = do return foot -- Main processing loop process :: Foot -> IO () process f = do c <- getChar -- Get a character putChar '\n' -- Return to keep the screen neat if c == '0' -- Is it an exit? then return () -- then leave else do f' <- manage c f -- otherwise manage request process f' -- continue to process -- Little usage message usage :: IO () usage = do putStr "0. Exit Program\n" putStr "1. Pull Trigger\n" putStr "2. Call Doctor\n" -- Main routine main :: IO () main = do usage -- Print usage process True -- Start processing with a good foot

1 0

ANNOUNCE: hmake-3.08
by Malcolm Wallace 23 Jun '03

23 Jun '03

hmake-3.08 ---------- http://www.haskell.org/hmake/ We announce a new release of hmake, the compilation manager for Haskell. This is essentially a bugfix release, to enable hmake to build cleanly with ghc versions >= 6.0. * Hmake should now build cleanly with GHC 6.0. * In hmake-interactive, if the readline library is not available, the replacement simple line editor now has a history mechanism. Regards, Malcolm

1 0

Re: Haskell-Cafe digest, Vol 1 #730 - 5 msgs
by Mark Espinoza 23 Jun '03

23 Jun '03

2 1

RE: Assembling lists start-to-end
by Hal Daume 21 Jun '03

21 Jun '03

sorry, forgot to send this to the list: Another way to do it is to use accumulating lists. As a simple example, let's consider: > myf p l = reverse (filter p l) (myf Char.isUpper "Hello Cruel World" ==> "WCH") that is, it returns elements of a list which match the predicate in reverse order. we could write this very slowly using explicit recursion as: > myf2 p [] = [] > myf2 p (x:xs) > | p x = myf2 p xs ++ [x] > | otherwise = myf2 p xs but traversing the recusive list is very slow. we might induce tail recursion in something like: > myf3 p l = myf3' l [] > where > myf3' [] acc = acc > myf3' (x:xs) acc = myf3' xs (x:acc) Now, the accumulator 'acc' holds the value we're going to return at the end. So this is pretty much what you want. Now, suppose we're just doing filter without the reversing, but we still want it to be tail recursive. We might think we have to write: > myf4 p l = reverse (myf3' l []) (where myf3' is as before) this is not so. We can have fun with function composition. What we do is change the accumulator from a list to a function from a list to a list. > myf4 p l = myf4' l id > where > myf4' [] acc = acc [] > myf4' (x:xs) acc > | p x = myf4' xs (\l -> acc (x:l)) > | otherwise = myf4' xs acc here, we start out the accumulator as the identity function. to add an element to it, we make a function which takes the old list, adds 'x' to the front and then applies the accumulator. in the base case, we simply apply the empty list to the accumulator function. the second-to-last line can be rewritten a bit more conveniently as: > | p x = myf4' xs (acc . (x:)) the neat thing about this is that you can easily change the way the list goes. as it is, we have filter, but if we flip the order for (.), as in: > | p x = myf4' xs ((x:) . acc) then we get (reverse . filter). HTH - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-cafe-admin(a)haskell.org > [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Mark Carroll > Sent: Saturday, June 21, 2003 5:39 AM > To: haskell-cafe(a)haskell.org > Subject: Assembling lists start-to-end > > > I am assembling a list from start to end. I can add elements > to the end > with "previous ++ [current]" or I can add them with "current > : previous" > and reverse it when I'm done. Or, maybe I should use some other data > structure. (I don't know the length in advance.) Any thoughts? > > -- Mark > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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IO system
by naudts guido 21 Jun '03

21 Jun '03

Hallo, Take following function: f::Array Int Char -> (Array Int Char, Char) f array = (array1, c) where c = array!1 array1 = array//[(2,'b')] and also following function: f::Direct_access_file -> (Direct_access_file, Char) f daf = (daf1, c) where c = getnext daf daf1 = set 2 'b' with a hypothetical format for the direct access file. Now I can certainly implement the first function in Haskell but not the second. Now the only difference between the two functions is the location of the data: in the first the data of the array are in RAM, in the second the data of the direct access file are on disk. There is no other difference. As far as referential integrity is concerened I don't see any difference too. So why can I implement the first function and not the second (well I can use direct access files but I have to change the type of my function.The problem is: I do not see why the location of data should have an influence here. Greetings, __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com

3 2

Using an accumulator, "iterating"...
by Brett Kelly 21 Jun '03

21 Jun '03

Hello all, I'm trying to write a function that takes a list and a element (same type) and returns the index of the first instance of the element in the list. like: getindex "brett" 'e' would return 2, etc. i'm trying to accomplish this using an accumulator, here's what i've got: pyindex :: Eq a => a -> [a] -> Maybe Int pyindex c l = pyindex' 0 chr (x:xs) where pyindex' count chr (x:xs) = do if x == chr then return count else pyindex' (count + 1) chr xs now, i know i've got a syntax problem, because i'm pretty sure my logic is correct (or at least MOSTLY correct). can anybody see what's wrong with my stuff? thanks! -- Brett Kelly bkelly(a)sourcereview.net This message has been digitally autographed using GnuPG. Vim - this ain't your daddy's text editor http://www.vim.org

5 6

Assembling lists start-to-end
by Mark Carroll 21 Jun '03

21 Jun '03

I am assembling a list from start to end. I can add elements to the end with "previous ++ [current]" or I can add them with "current : previous" and reverse it when I'm done. Or, maybe I should use some other data structure. (I don't know the length in advance.) Any thoughts? -- Mark

3 2

RE: Help: Stack-overflow and tail-recursive functions
by Hal Daume 21 Jun '03

21 Jun '03

> GHCi didn't have any problem even with the original code. mine didn't either, until I increased the "200" to around "1500"...it's probably OS/memory specific.

2 1

Help: Stack-overflow and tail-recursive functions
by Koji Nakahara 20 Jun '03

20 Jun '03

Hi I've written a function that is tail-recursive and takes a list(queue) as one of its arguments. However the function fails because of "Stack space overflow"(GHC) or "ERROR - Garbage collection fails to reclaim sufficient space"(hugs). For example (simplified), both of these results in stack-overflow: f1 100000 [0,1,2], and even f2 100000 [0,1,2], where, f1 0 l = l f1 n l = f (n-1) $ take 3 $ l ++ [0,1] f2 0 l = l f2 n l = f2 (n - 1) $! (take 3 $ l ++ [0,1]) Why f2 overflows? How to avoid this stack-overflow?

1 1

Re: Help: Stack-overflow and tail-recursive functions
by oleg＠pobox.com 20 Jun '03

20 Jun '03

It seems the problem is indeed in rmat: > rmat n = listArray ((1,1),(n,n)) $ map ct (randoms (mkStdGen 1) ::[Bool]) > where ct True = Unknown > ct False = Dead To be more precise, the problem is in randoms. If you replace rmat with the following rmat n = array ((1,1),(n,n)) $ zipWith (\ind v -> v `seq` (ind,v)) [(i,j) | i<-range, j<-range] $ map ct (randoms (mkStdGen 1) ::[Bool]) where ct True = Unknown ct False = Dead range = [1..n] then > main = putStrLn $ show $ forpaintbdry $ rmat 400 computes without problems (compiled with GHC 5.04.1, no flags). BTW, GHCi didn't have any problem even with the original code.

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RE: Help: Stack-overflow and tail-recursive functions
by Hal Daume 19 Jun '03

19 Jun '03

The problem here is actually in the rmat function, not the forpaintbdry or whatever. The problem is that, afaik, the listArray function doesn't deforest the list argument (someone can correct me here, though). That is, you write: rmat n = listArray ... [a big list] and then this list is first built, then the array is filled in. You can see that this is a problem by replacing your main with: main = print (m ! snd (bounds m)) where m = rmat 800 This will stack overflow too. Solution: use mutable arrays and fill them in by hand :). -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: Koji Nakahara [mailto:yu-@div.club.ne.jp] > Sent: Wednesday, June 18, 2003 7:41 PM > To: Hal Daume; haskell-cafe(a)haskell.org > Subject: Re: Help: Stack-overflow and tail-recursive functions > > > On Wed, 18 Jun 2003 17:36:28 -0700 > "Hal Daume" <t-hald(a)microsoft.com> wrote: > > > Note that there is essentially no difference between f1 and > f2. When > > you $! in f2, all it does is ensure that the argument isn't > undefined. > > It doesn't evaluate any of the list. Try $!! from the > DeepSeq module or > > write your own list-forcing function. > > Thank you very much. I understand. > > However my original program still (or maybe from the > beginning) stack-overflows > at another point, in the middle of the evaluation of "forpaintbdry". > > Please give me some advice. > ----------- > -- snippet of the program for painting a random matrix from > its boundary. > module Main where > import System > import Random > import Array > import Ix > import List > > main = putStrLn $ show $ forpaintbdry $ rmat 200 > > forpaintbdry m = [(pos, Live) | pos <- (uncurry bdryidxlist) > $ bounds m , isUnknown $ m ! pos ] > > bdryidxlist :: (Int, Int) -> (Int, Int) -> [(Int, Int)] > bdryidxlist (a1, a2) (b1, b2) = nub $ [(ab, j) | ab <- [a1, > b1], j <- [a2..b2]] ++ > [(i, ab) | ab <- [a2, b2], i <- > [a1..b1]] > > rmat n = listArray ((1,1),(n,n)) $ map ct (randoms > (mkStdGen 1) ::[Bool]) > where ct True = Unknown > ct False = Dead > > data CellColor = Live | Unknown | Dead > > isUnknown Unknown = True > isUnknown _ = False > > instance Show CellColor where > show Live = "Live" > show Unknown = "Unknown" > show Dead = "Dead" > >

1 0

RE: Help: Stack-overflow and tail-recursive functions
by Hal Daume 19 Jun '03

19 Jun '03

Note that there is essentially no difference between f1 and f2. When you $! in f2, all it does is ensure that the argument isn't undefined. It doesn't evaluate any of the list. Try $!! from the DeepSeq module or write your own list-forcing function. For me, the following works: f1 0 l = l f1 n l = f1 (n-1) $!! (take 3 $ l ++ [0,1]) f $!! x = force x `seq` f x where force [] = () force (x:xs) = x `seq` force xs whereas it doesn't without the $!!. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-cafe-admin(a)haskell.org > [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Koji Nakahara > Sent: Wednesday, June 18, 2003 5:18 PM > To: haskell-cafe(a)haskell.org > Subject: Help: Stack-overflow and tail-recursive functions > > > Hi > > I've written a function that is tail-recursive and takes > a list(queue) as one of its arguments. > However the function fails because of > "Stack space overflow"(GHC) or "ERROR - Garbage collection > fails to reclaim sufficient space"(hugs). > > For example (simplified), both of these results in > stack-overflow: f1 100000 [0,1,2], and even f2 100000 [0,1,2], > > where, > f1 0 l = l > f1 n l = f (n-1) $ take 3 $ l ++ [0,1] > > f2 0 l = l > f2 n l = f2 (n - 1) $! (take 3 $ l ++ [0,1]) > > Why f2 overflows? > > How to avoid this stack-overflow? > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskel> l-cafe >

2 1

Re: Type classes and code generation
by Keith Wansbrough 17 Jun '03

17 Jun '03

> You need to change the first line to this: > > > data C a = C { pair :: forall b. b -> (b,a) } > > and then it works fine (with -fglasgow-exts). But you've now stepped > outside the bounds of Haskell 98. (oops, replying to myself... sure sign of madness! :) ) I hasten to add that this is *not* the same as existential quantification; note carefully the location of the forall wrt the constructor. --KW 8-) -- Keith Wansbrough <kw217(a)cl.cam.ac.uk> http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory.

1 0

Re: Type classes and code generation
by Hal Daume III 17 Jun '03

17 Jun '03

(Moved to the Cafe) > Yes, exactly. Every class is translated to a data type declaration, > and every instance is translated to an element of that data type - a > dictionary. (Note that you can't actually write those declarations in > Haskell 98 in general, because they can have polymorphic fields; but > this is a simple extension to the language). Keith, could you elaborate on this parenthetical? Under what circumstances can you not create the dictionary datatype for a class in Haskell 98 (where the class itself is H98 :P)? - Hal

2 1

Protect your privacy
by Software Promote Center 17 Jun '03

17 Jun '03

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1 0

Please contact me
by Joseph Makale 17 Jun '03

17 Jun '03

MR. JOSEPH MAKALE DEPARTMENT OF MINERALS AND ENERGY PRETORIA, SOUTH AFRICA. JUNE16TH., 2003 Sir, It is my great pleasure to write you this letter on behalf of my colleagues. Your information was given to me by a member of the South African Export Promotion Council (SAEPC) who was with the Government delegation on a trip to your country for a United Nations bilateral conference talk on sustainable development to encourage foreign investors. I have decided to seek a confidential co-operation with you in the execution of a deal here-under for the benefit of all parties and hope you will keep it confidential because of the nature of the business. Within the Department of Minerals and Energy where I work as an assistant Director of Audit, with the co-operation of two other top officials, we have in our possession an overdue contractor payment in US Dollars funds. The said funds represent certain percentage of the contract value executed on behalf of my Department by a foreign contracting firm, (Pearls Ltd) which we the officials over-invoiced to the amount of US$15,200,000 (Fifteen Million Two Hundred Thousand US Dollars). Since the present elected Government is determined to pay foreign contractors all debts owed, so as to maintain good relations with foreign governments and non-governmental agencies, we included our bills for approvals with the Department of Finance and the Reserve Bank of South Africa (RBSA). We are 100+% sure of funds approvals to anyone or company we (The Audit Committee) recommend as part of the sub-contractors who did jobs for the Department. We are seeking your assistance to front as the sub-contractor of the unclaimed funds, since we are not allowed to operate foreign accounts. Details and change of beneficiary information upon application for claim to reflect payment and approvals will be secured on behalf of You/your Company. My colleagues and I are prepared to give you US$2.5m while we take US$7.4m and the balance of US$5.3m for taxes and miscellaneous expenses incurred. This business is completely safe and secure, provided you treat it with utmost confidentiality. It does not matter whether You/your Company does contract projects, as a transfer of rights will be secured in favor of You/your Company through the Federal high Court of South Africa before we can proceed. I have reposed my confidence in you and hope that you will not disappoint us. Kindly notify me immediately for further details upon your acceptance of this proposal. You can contact me by email. Yours Faithfully, Joseph Makale (Mr.)

1 0

Italian-crafted Rolex - only $65 - $140!! Free SHIPPING ! !
by tony2003＠yahoo.ca 16 Jun '03

16 Jun '03

1 0

gtk2hs
by Christian Buschmann 16 Jun '03

16 Jun '03

Hi! I tried to implement a simple counter with gtk2hs. To increase my counter I defined following event: onClicked btn $ do si <- textBufferGetStartIter tb ei <- textBufferGetEndIter tb val <- textBufferGetText tb si ei False textBufferSetText tb $ show $ (+1) $ read val But now I don't want always read the textfield to get my counter-value, I would like to save the state of my increased value and would like to pass it to the next call of the function. How can I do this? thanks Christian This is the complete code: import Gtk quitDialog :: IO Bool quitDialog = ..... main :: IO () main = do initGUI --main window win <- windowNew onDelete win (\_->(quitDialog>>= (return . not ))) onDestroy win mainQuit vb <- vBoxNew True 5 hb <- hBoxNew True 5 btn <- buttonNewFromStock stockExecute btn2 <- buttonNewFromStock stockQuit tv <- textViewNew tb <- textBufferNew Nothing textBufferSetText tb "0" textViewSetEditable tv False textViewSetCursorVisible tv False textViewSetBuffer tv tb boxPackStartDefaults vb tv boxPackStartDefaults vb hb boxPackStartDefaults hb btn boxPackStartDefaults hb btn2 hgf <- onClicked btn $ do si <- textBufferGetStartIter tb ei <- textBufferGetEndIter tb val <- textBufferGetText tb si ei False textBufferSetText tb $ show $ (+1) $ read val disconnect hgf onClicked btn2 $ do quit <- quitDialog if quit then widgetDestroy win else return () containerAdd win vb widgetShowAll win mainGUI

2 1

未承諾広告＊５億９千万円収入証拠から３億円へ一歩　　　
by ５億９千万円証拠有ビジネス 15 Jun '03

15 Jun '03

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1 0

no subject
by Team domeus 15 Jun '03

15 Jun '03

Hello haskell-cafe(a)haskell.org, You successfully unsubscribed from the group intelligentlearning(a)domeus.co.uk. You will not receive any more messages from this group. Best regards, Your Domeus Team

1 0

Welcome to the group Intelligent Learning
by Team domeus 15 Jun '03

15 Jun '03

Hello haskell-cafe(a)haskell.org, You have been added to the group Intelligent Learning (intelligentlearning(a)domeus.co.uk) The group owner sends the following welcome message: ---------------------------- Welcome to Intelligent Learning! Our systems and programs can help you to successfully optimize your professional potential in a changing world. To be able to progress efficiently in any area today, we promote new smart working and learning systems through new techniques, tools and methodologies (TTMs) in key Smart Learning Areas: Knowledge Management, Change Management, Quantitative Learning, Qualitative Learning, Skill Management and Business Intelligence. For more information visit our web www.amjsmartlearning.com info(a)amjsmartlearning.com ---------------------------- If you do not wish to receive mails from this group, please return this eMail by clicking on reply. Alternatively, you can send an eMail to intelligentlearning-unsubscribe(a)domeus.co.uk. To unsubscribe via the web please use the following link: http://uk.domeus.com/public/unsubscribe.jsp?tsp=1055676075383&gid=337463&ui… Either way you will be directly deleted from the distribution list. If you have any questions or concerns, please contact the moderators of this Domeus group at intelligentlearning-moderators(a)domeus.co.uk. If your eMail address has been added to this list without your consent and you do not wish to receive any eMails from Domeus, please forward this message to: set_account_inactive(a)domeus.co.uk. Please note that this will disable your eMail address throughout the Domeus system. If you have any questions or problems concerning domeus please contact admin(a)domeus.co.uk. Best regards, Your Domeus Team

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Haskell.org out of date
by Hampus Ram 15 Jun '03

15 Jun '03

Who takes care of haskell.org? If it is the "community" we're obviously not doing it right, lots of broken links and some that is there but does not work (e.g. the wish-list). Only the "libraries and tools" page contains 16 broken links (according to linkchecker.sf.net) and some of the tools should in my opinion be marked clearly with "antique" so you do not get upset when they require ghc 2 to compile without problem... /Hampus - (I can't decide where it's best to post this...) -- Homepage: http://www.dtek.chalmers.se/~d00ram E-mail: d00ram(a)dtek.chalmers.se "Det är aldrig försent att ge upp"

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REPLY REQUIRED: Confirm subscription to group Intelligent Learning
by Team domeus 14 Jun '03

14 Jun '03

Hello haskell-cafe(a)haskell.org, thanks for your interest in the group Intelligent Learning (intelligentlearning(a)domeus.co.uk) If you would like to accept this invitation, please return this eMail by clicking on reply or subscribe via the Web. http://uk.domeus.com/public/subscribe.jsp?tsp=1055553244893&gid=337463&uid=… If you are not interested in joining, please ignore this eMail and you will receive no further eMails from us. The group owner sends the following welcome message: ----------------------------- Welcome to Intelligent Learning! Our systems and programs can help you to successfully optimize your professional potential in a changing world. To be able to progress efficiently in any area today, we promote new smart working and learning systems through new techniques, tools and methodologies (TTMs) in key Smart Learning Areas: Knowledge Management, Change Management, Quantitative Learning, Qualitative Learning, Skill Management and Business Intelligence. For more information visit our web www.amjsmartlearning.com info(a)amjsmartlearning.com ----------------------------- If you would like to use the full range of features, just log in at http://uk.domeus.com using the following log-in information: username: haskell-cafe(a)haskell.org password: fetifak8 If your eMail address has been added to this list without your consent and you do not wish to receive eMails from Domeus, please forward this message to: set_account_inactive(a)domeus.co.uk. Please note that this will disable your eMail address throughout the Domeus system. Best regards, Your Domeus Team

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Testing was Re: main modules in GHC, deriving differences between GHC and Hugs
by Matthew Donadio 14 Jun '03

14 Jun '03

(redirected to haskell-cafe) Hal Daume III wrote: > Yes, but there's a problem with this solution. Namely, if Foo.hs takes a > long time to compile, then you can't leverage having already created Foo.o > and Foo.hi when making the Main. Yeah, it's not perfect, but I think we just have different methodologies for testing. Typically, I do most of my development with ghci or hugs. Each module will have a single variable that represents the tests tests :: [Bool] tests = [ test1, test2, test3 ... ] and then I define a variable called test :: Bool test = and tests so I can just load a module and either evaluate tests or test to check things out. This generalizes to importing and testing several modules at once (as long as I take care of name conflists). This only works for simple modules, though. For more complicated ones, I have a "pretty" tester. For example, my Haskell FFT library is collection of mutually recursive modules. I have a specialzed test function for this that tests a range of lengths. It looks someone like main = testfft n1 n2 testfft n1 n2 = sequence $ map test1fft [n1..n2] test1fft n = do putStr $ show n ++ ":\t" putStr $ if ok then "OK\n" else "ERROR\n" where ok = and [ test1 n, test2 n, test3 n ] This way I can compile the code, and run the executable as ffttest 2 2048 | grep ERROR and I am confident that I get full coverage of the algorithm. I am always to hear about other methods of automated testing. -- Matthew Donadio (m.p.donadio(a)ieee.org)

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powerset
by Graham Klyne 13 Jun '03

13 Jun '03

A brief search of the libraries didn't reveal (top me) a ready-to-roll powerset function. I thought this may be a useful exercise to see how well I'm picking up on functional programming idioms, so I offer the following for comment: [[ -- |Powerset of a list, in ascending order of size. -- Assumes the supplied list has no duplicate elements. powerSet :: [a] -> [[a]] powerSet as = foldl (++) [] [ combinations n as | n <- intRange 1 (length as) ] -- |Combinations of n elements from a list, each being returned in the -- order that they appear in the list. combinations :: Int -> [a] -> [[a]] combinations _ [] = [] -- Don't include empty combinations combinations n as@(ah:at) | n <= 0 = [[]] | n > length as = [] | n == length as = [as] | otherwise = (map (ah:) $ combinations (n-1) at) ++ (combinations n at) -- |Return list of integers from lo to hi. intRange :: Int -> Int -> [Int] intRange lo hi = take (hi-lo+1) (iterate (+1) 1) -- Tests testcomb0 = combinations 0 "abcd" -- [] testcomb1 = combinations 1 "abcd" -- ["a","b","c","d"] testcomb2 = combinations 2 "abcd" -- ["ab","ac","ad","bc","bd","cd"] testcomb3 = combinations 3 "abcd" -- ["abc","abd","acd","bcd"] testcomb4 = combinations 4 "abcd" -- ["abcd"] testcomb5 = combinations 5 "abcd" -- [] testpower = powerSet "abc" -- ["a","b","c","ab","ac","bc","abc"] ]] I think the recursive use of 'combinations' may be inefficient, and could maybe be improved by "memoizing"? #g ------------------- Graham Klyne <GK(a)NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E

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Green Card and Exceptions
by Matthew Donadio 13 Jun '03

13 Jun '03

Hi all, I have a couple of questions about Green Card and exceptions. I am interfaceing to the GSL to get access to a few functions, and eventually interface all of the special functions to Haskell. And unlike my DSP library, and am trying to get it right the first time. :) Below is a Green Card interface to one of the functions. %fun airy_Ai_e :: Double -> (Double, Double) %call (double x) %code int rc; % double val; % double err; % gsl_sf_result result; % rc = gsl_sf_airy_Ai_e(x, GSL_PREC_DOUBLE, &result); % val = result.val; % err = result.err; %result (double val, double err) This definition works, but it ignores the return code from the library function. The various return codes are from an enum defined in a header file. I would like to throw a Haskell exception (one of the ArithExceptions defined in Control.Exception) depending on the value of "rc". Do I need to create a new DIS for the return values (which are an enum defined in a header), change the function to return a triplet (var,err,rc), and then throw the exception in Haskell land? Is there a way I can do this directly from the GC interface? If I have to create a DIS, can this be shared across several modules that all need the same functionality? Thanks. -- Matthew Donadio (m.p.donadio(a)ieee.org)

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chance to help out on the wiki
by Isaac Jones 13 Jun '03

13 Jun '03

Greetings. We added a page "Fundamental Concepts" to the wiki so that we might have a very specific reference to pass along to people with questions, and to add links to definitions throughout the wiki. http://www.haskell.org/hawiki/FundamentalConcepts A lot of concepts need to be filled in, and if you haven't participated in the Wiki yet, now is a good time :) If you've never used a wiki, you can read about it here: http://www.haskell.org/hawiki/HelpForBeginners You might model your explanations after a page I wrote for PatternMatching which has: - a reference to a tutorial - a reference to the haskell report - an explanation - some examples Feel free to extend and / or correct anything already there. The front page of the wiki is here: http://www.haskell.org/hawiki/FrontPage peace, isaac

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