- Haskell-Cafe - Haskell.org

System.Random StdGen read fails on some strings?
by Fritz Ruehr 19 Mar '07

19 Mar '07

According to the documentation for System.Random (see <http:// haskell.org/ghc/docs/latest/html/libraries/base/System-Random.html>): > In addition, read may be used to map an arbitrary string (not > necessarily one produced by show) onto a value of type StdGen. In > general, the read instance of StdGen has the following properties: > > * It guarantees to succeed on any string. > * ... On the other hand, I get the following on the (admittedly stupid, spur-of-the-moment) String argument "whateva": > Hugs> :l System.Random > System.Random> read "whateva" :: StdGen > > Program error: Prelude.read: no parse > > System.Random> map read $ words "this is a test of the System dot > Random StdGen read, which seems to fail only on ... whateva" :: > [StdGen] > [4580 1,440 1,101 1,4584 1,445 1,1485 1,35261 1,1377 1,32825 > 1,34047 1,13422 1,14037 1,13637 1,469 1,4132 1,4514 1,453 1,626 1, > Program error: Prelude.read: no parse Am I missing something here? Or am I just being punished for the stupidity of my particular choice of String? :) -- Fritz PS: this happens with both Hugs Version: September 2006 and GHC Interactive, version 6.6, running on Mac/Tiger, for what that's worth.

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Type synonym application
by C Rodrigues 19 Mar '07

19 Mar '07

Type synonyms aren't applied as I would expect during kind checking. What's going on here? type WithList a b = b [a] type FooPair a b = (b, a -> b) -- error: `WithList' is applied to too many type arguments ints1 :: WithList Int FooPair [Int] ints1 = ([1], id) -- error: `FooPair' is not applied to enough type arguments ints2 :: (WithList Int FooPair) [Int] ints2 = ([1], id) -- after manually applying the first type synonym ints3 :: FooPair [Int] [Int] ints3 = ([1], id) _________________________________________________________________ Live Search Maps find all the local information you need, right when you need it. http://maps.live.com/?icid=hmtag2&FORM=MGAC01

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Re: [Haskell] Haskell Chess
by Andrew Wagner 19 Mar '07

19 Mar '07

Andrzej, I'd love to hear some of your thoughts on these things. I agree with you about brute-force not being the best approach in haskell (or maybe at all). I think we should switch to haskell-cafe, since that's where much of this discussion has gone, and that's more for extended discussions anyway. On 3/18/07, Andrzej Jaworski <himself(a)poczta.nom.pl> wrote: > Didactic it may be but brute force on search trees means in Haskell problem > with garbage collection. So students may build a punch but loose a street > fight. > > Instead of using Haskell as a hammer I would rather explore what monadic > programming can offer in terms of encapsulating constraints, heuristics, > modal logic or agents. Chess is a human game so why not use computing along > this line and employ Haskell on humane terms? The force is with us! > > Cheers, > -Andrzej > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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Re: [Haskell] Summer of Code project proposal
by Neil Mitchell 19 Mar '07

19 Mar '07

Hi Nikhil, haskell-case is probably a better choice of list for this - haskell is more for announcements. > > I am Nikhil N, a third year Computer Science student from India. I am > looking at building a good > IDE for people learning Haskell(as part of SoC).This IDE will be modeled > on Dr Scheme or blueJ. Have you looked at something based on HIDE or GuiHaskell? The latter is certainly in the SoC database (I added it), the former was an active project a while ago. How much work do you think is involved in writing an IDE? I suspect its a massive amount - much more than one summers worth.... Thanks Neil

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Re: Performance Help
by Dominic Steinitz 19 Mar '07

19 Mar '07

Thanks. > Fusing the ws is trickier. Directly appealing to the fibonacci-number > example is not recommended because this would mean to keep the last 16 > ws in memory and shifting them right to left by hand. But as the Are you saying this because we don't want a 16-tuple? > "Alternate method of computation" on the website suggests, you can > delegate the shifting to an index that shifts around mod 16. Having a > mutable array is helpful, then. Are you saying that because haskell doesn't really have mutable arrays, this is ruled out? > Of course, you can also fill a large static (boxed!) array of 80 Word8s via > > ws :: Data.Array.IArray.Array Int Word8 > ws = accumArray 0 (0,80) (curry snd) $ > zip [0..15] xs ++ [(i, xxor i) | i<-[16..80]] > where > xxor i = ws ! (i-16) `xor` > ws ! (i-3) `xor` ws ! (i-8) `xor` ws ! (i-14) > > or something like that (I didn't care about correct indices and bounds). > GHC can fuse such array accumulations. Why is an array better than a list? Is it because (!) is O(1) and (!!) is O(n)? > > In general, keeping stuff in lists is not wrong, but ByteStrings are > more adapted to current CPU and RAM architecture. I'm not clear how ByteStrings help here. We need to put bits into 32 words and operate on these. Dominic.

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Re: Re: HS-Plugins 1.0 chokes on simple test, WinXP GHC-6.6 (Conal Elliott)
by Vivian McPhail 19 Mar '07

19 Mar '07

Hi, I just setup and installed hs-plugins from darcs on WinXP using ghc-6.6 and MSYS. The hs-plugin test suite all passes. Can you send me something that generates your error and I'll have a look at it. Vivian > Message: 2 > Date: Sat, 17 Mar 2007 18:06:12 -0700 > From: "Conal Elliott" <conal(a)conal.net> > Subject: Re: [Haskell-cafe] Re: HS-Plugins 1.0 chokes on simple test, > WinXP GHC-6.6 > To: haskell-cafe(a)haskell.org, "Donald Stewart" <dons(a)cse.unsw.edu.au> > Message-ID: > <ea8ae9fb0703171806h641da4a8q28fa19b86bd2ad85(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Glad to know, Ian. Thanks. > > I'd sure love to have a working hs-plugins again, especially > in time to help with my ICFP submission. I wouldn't begin to > know how to crack something like this bug. Does anyone have > any ideas? > > Cheers, - Conal > > > On 3/17/07, Ian Lynagh <igloo(a)earth.li> wrote: > > > >c:/ghc/ghc-6.6/HSbase.o: unknown symbol `_free' > > > > > > > > >Don mentioned this is a known problem. Is it on > anyone's todo list? > > > > Not mine. > > > > > > > On 3/17/07, Ian Lynagh <igloo(a)earth.li> wrote: > > > > On Fri, Mar 16, 2007 at 09:52:10PM -0700, Conal Elliott wrote: > > > BTW, to get hs-plugins to build, I changed two lines in > > > hs-plugins/configure. > > > > As it happens, I sent Don a similar patch last night, so hopefully > > it'll be fixed in darcs soon. > > > > > First I tried tr -d '\n', but it didn't work, and I don't > know why. > > > > Because it's a \r you're trying to delete. > > > > > On 3/16/07, Conal Elliott <conal(a)conal.net> wrote: > > > > > > > >I got hs-plugins to compile fine on winxp, but now when > I run it I > > > >get > > a > > > >crash with this message: > > > > > > > >c:/ghc/ghc-6.6/HSbase.o: unknown symbol `_free' > > > > > > > >Don mentioned this is a known problem. Is it on > anyone's todo list? > > > > Not mine. > > > > > > Thanks > > Ian > > > > >

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Visibility of definitions in Hugs Prelude
by Fritz Ruehr 19 Mar '07

19 Mar '07

I am wondering about the visibility of definitions in the Hugs Prelude. More specifically, when I ask for info about the Eq class, I see a lot of instances, including: > instance Eq Key On the other hand, Key is not in scope: > Hugs> :info Key > Unknown reference `Key' I imagine this has to do with importing/exporting, or maybe some modern Hugs empty-Prelude funkiness. Or perhaps it is because Key is a "non-standard export" (but that is just a comment in the Prelude). In any case, is it intended that ":info" will tell me about things that I (and it) can't otherwise see? Please forgive my naivete re module rules in advance ... . -- Fritz

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Using external programs with Haskell in windows.
by Christian Lean 18 Mar '07

18 Mar '07

I'm looking for a way to run an external program and get the results in haskell. Something similar to HSH but that will work in windows. I don't need anything too complex, just to provide the command to be run as a string and get the result as a string. Is this possible? One of the HSH examples is all I need: runS $ "echo /etc/pass*" -> "/etc/passwd /etc/passwd-"

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Stack Space Overflow.
by John T Davis 18 Mar '07

18 Mar '07

oHello, I'm writing a simulation of a game of Nim with genetic programming. I've run into a stack space overflow problem with one of my functions (part of a class instance), which I've included below. crossover_mutate enp = enp { progPop = ansPop, numProgs = (numProgs enp) + (crossNum enp)} where crossResult = crossNimPlayerPop (progPop enp) (seed enp) (theBoard enp) (numProgs enp) (crossNum enp) mutateResult = mutateNimPlayerPop crossResult (mutateRatio enp) popParts = crossResult ++ mutateResult newPop = Set.toAscList (Set.fromList popParts) ansPop = tournament (newPop, newPop) (theBoard enp) Now, here's where it gets weird. I've got test data that I've run all the constituent functions (crossNimPlayerPop, mutateNimPlayerPop, tournament) on, and they all work as they should. Now, when I run the same data on crossover_mutate, I get the aforementioned stack space overflow. I'm totally stumped on this... I've even run the equivalent of ansPop on the command line, and despite how truly unreadable the code is in that format, it runs fine. Any suggestions or thoughts would be greatly appreciated. Have a nice day. :-) Thank you, John T Davis

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Does inlinePerformIO = unsafePerformIO . unsafeInterleaveIO semantically?
by Isaac Dupree 18 Mar '07

18 Mar '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Compare the guarantees (in practice and/or theoretically) of inlinePerformIO and unsafePerformIO . unsafeInterleaveIO (i.e. function composition) (aside from inlinePerformIO being better optimized). Are they the same, or if not, what do they mean - what are the differences? Not yet understanding any of these operations fully, Isaac -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFF/QsBHgcxvIWYTTURAtC6AJ4rKqhfmVi5cLC2MhXF9J4Pxk30KQCdGnQ7 Wd0BrIreZhIc0Gzm/tQLa78= =poy9 -----END PGP SIGNATURE-----

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