November 2007 - Haskell-Cafe

St. Petersburg Game
by manolo＠austrohungaro.com 27 Nov '07

27 Nov '07

Hello, I'm trying to program an implementation of the St. Petersburg game in Haskell. There is a coin toss implied, and the random-number generation is driving me quite mad. So far, I've tried this: import Random increment :: Int -> Int increment b = b + 1 main = do let b = 0 let c = randomRIO (1,2) until (c == 1) increment b return b This is intended to print the number of consecutive heads (i.e., 2) before the first tail, but I get the following error: ERROR "StPetersburg.hs":8 - Type error in application *** Expression : until (c == 1) increment b *** Term : c == 1 *** Type : Bool *** Does not match : Int -> Bool I don't really see what's going on, so any help will be more than welcome. I hope this is a suitable question for the Haskell Café list. I'm using Hugs in an Ubuntu box, in case that should be useful. Thanks, Manolo

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return in Monad class necessary?
by Henning Thielemann 27 Nov '07

27 Nov '07

I wonder whether it is a typical mistake of beginners to write 'return' within a do-block (that is, not at the end) and if it is possible to avoid this mistake by clever typing. In a proper monad 'return' can be fused with subsequent actions, and thus it is not necessary within a sequence of actions. However, although sensible, 'return' is also not required at the end of a block. Has someone already thought about a replacement for monads?

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Browser action and new http library
by bbrown 27 Nov '07

27 Nov '07

I am trying to use the HTTP library 3001 for ghc 6.8 and cant figure out how to use a proxy to do a GET request as I am behind a proxy server. My thinking is that I could use the setProxy method it looks like it returns a BrowserAction? What do I do with that. Here is the current code (I havent really used the setProxy yet). -- -- HTTP LIBRARY version: HTTP-3001.0.2 import Data.Char (intToDigit) import Network.HTTP import Network.URI import Network.Browser (defaultGETRequest) import System.Environment (getArgs) import System.Exit (exitFailure) import System.IO (hPutStrLn, stderr) main = do args <- getArgs case args of [addr] -> case parseURI addr of Nothing -> err "Could not parse URI" Just uri -> do cont <- get uri putStr cont _ -> err "Usage: lman <url>" err :: String -> IO a err msg = do hPutStrLn stderr msg exitFailure get :: URI -> IO String get uri = do eresp <- simpleHTTP (defaultGETRequest uri) resp <- handleErr (err . show) eresp case rspCode resp of (2,0,0) -> return (rspBody resp) _ -> err (httpError resp) where showRspCode (a,b,c) = map intToDigit [a,b,c] httpError resp = showRspCode (rspCode resp) ++ " " ++ rspReason resp -- -- Handle Connection Errors handleErr :: Monad m => (ConnError -> m a) -> Either ConnError a -> m a handleErr h (Left e) = h e handleErr _ (Right v) = return v -- End of File -- Berlin Brown [berlin dot brown at gmail dot com] http://botspiritcompany.com/botlist/?

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Announce: strict-concurrency
by Don Stewart 26 Nov '07

26 Nov '07

While writing some multi-core concurrent code I needed more precise control over which thread evaluated particular expressions. The default concurrent types, MVar and Chan, are lazy, and sometimes not suitable. The little package, http://hackage.haskell.org/cgi-bin/hackage-scripts/package/strict-concurren… Provies the MVar type, but with strict putMVar by default, and an element-strict Chan type. For some applications, these stricter types can yield improved time and space use. (For others, they can make things worse) The strict channel type in particular seems useful, as it can be used to force worker threads to evaluate to WHNF before returning values to a driver thread. Enjoy, Don

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Pretty-printing peg solitaire boards
by Maurício 26 Nov '07

26 Nov '07

Hi, I'm trying to pretty-print (with Text . PrettyPrint . HughesPJ) a set of peg solitaire boards. No matter what I try, I always get this: 00# 00# 0000#00 0000000 0000000 000 000 : 00# 00# 0000000 0000000 0000000 000 000 but what I really want is this: 00# 00# 00# 00# 0000#00 0000000 0000000 : 0000000 0000000 000 000 000 000 000 What I'm I doing wrong? When I have two boards a,b::Doc, I'm composing them with a <+> colon <+> b and rendering them with just 'render'. Should I try something else? Thanks, Maurício

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Re: [Haskell-cafe] New demo/test program for Yhc Javascript backend
by Thomas Hartman 26 Nov '07

26 Nov '07

Fair enough, I can wait for a couple of days. You might want to fix thartman@none:~/haskell-installs/yhc-install/yhc/src/translator/js/test>darcs whatsnew { hunk ./src/translator/js/test/Makefile 12 - $(YHC) -includes ../lib/haskell -linkcore $< + $(YHC) --includes ../lib/haskell --linkcore $< } immediately though. This is the only makefile for the javascript stuff in the repo, and it doesn't work because of - instead of --. Given your darcs log message that the javascript compiler would be broken I initially assumed that was the reason and not a flags change. More questions. So okay, it builds, I have Test1.html. It's a blank file with a bunch of javascript. I have firebug, so I can ask execute stuff in the javascript console. But I can't figure out what to execute. factorial isn't there, nor sumlst... none of the interesting looking functions? So what is this supposed to do? And can I change the makefile so that at least it generates javascript where I can execute the interesting functions in the firebug console? thomas. 2007/11/26, Dimitry Golubovsky <golubovsky(a)gmail.com>: > Thomas, > > OK, let's try to get on the same page regarding where the project is. > > The Javascript generator is maybe not optimal, but it works. > > DOM bindings are generated from W3C's IDL files, so everything DOM > provides may be used by Haskell programs, whether in CPS notation, or > monadic, this will become clear, which form to use, in the near > future. > > The recent HsWTKDemo works well in major browsers (FF, MSIE, Opera) > except for Safari, but this is probably a hard case due to the lack of > debugging information. > > If you look at its source http://darcs.haskell.org/yhc/web/jsdemos/HsWTKDemo.hs > > (no, you cannot compile it at the moment because it is plain CPS) you > may see some stuff related to static page layout definition in > declarative way (look for upcntW, factW, etc.) This part is almost > finalized wrt notation. What's left undecided is whether to use plain > CPS notation, or monadic notation for parts of the code that involve > imperative stuff (see e. g. updateD function where node's children are > replaced in order to update what's displayed). > > This all works perfectly in plain CPS. Understanding that nowadays > Monads are mainstream, I am trying to adopt monadic notation based on > the Cont monad instead of plain CPS. I ran one example (EchoM) on MSIE > and noticed memory leaks on each user's action. However when the page > is unloaded, MSIE shrinks in size which is a good sign. I think I know > where the cause is, tonight I'll try to fix it. If unsuccessful, I'll > probably unroll all monadic changes. > > Next steps are: > > 1. Finalize the code notation for static layout and imperative part > and check the base library into the Yhc repo > > 2. Generate haddock documentation > > 3. Write a better documentation for developers > > 4. Set up a web service that would allow everybody to submit their > Haskell source and generate HTML page with Javascript in response; > this I think can be done based on the hpaste program (backed by > Happs). > > Just for now, you have to wait a couple days while I am straightening > the monadic thing out. I'd appreciate if you look at the code of > HsWTKDemo and give me your impressions about notation, etc. > > Thank you. > > -- > Dimitry Golubovsky > > Anywhere on the Web >

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idea for ycr2js demo, actually meant for an in-house project. is this realistic?
by Thomas Hartman 26 Nov '07

26 Nov '07

As I mentioned in a previous post, I've been spending quite some time trying to get live with ycr2js because there's a project it would be useful for for my day job, as well as making another nice demo to add to the list. Basically, I have some functionality that does client-side filtering of large html tables. It's pretty smart -- it can filter on multiple columns, and the filter can be any javascript expression from String -> Bool (to use haskell terminology in a javascript context). The filter works by hiding rows that don't match the filter; it's built on mochikit. Unfortunately this is rather ugly from the user's perspective. You have to type something like x.match("my string") into the search string or (x > 5 && x < 7) where x is some variable buried in the javascript. I would like for the user to be able to enter search criteria in a more intuitive "google" style =skittles or (=~"mr. goodbar" and =~"15 grams") so you need a parser that takes the search criteria and converts it into a function from (String -> Bool) This parser is relatively easy to build in haskell; I built it. It's surely also doable in javascript, but not as nicely, easily, and cleanly, and being a better haskell than javascript programmer as well, I would rather generate the javascript from haskell. So at any rate what I have is -- parser from String -> (String -> Bool) (haskell) -- working html/javascript built on mochikit that filters a multicolumn table with multiple filter expressions. There is a function here that takes a string and returns a bool, but it's icky, doesn't recognize quoted strings, doesn't recognize boolean and/or or parentheses. I want to replace it with a function generated from haskell that does all of these things. What I need is to combine these two components. I'll try and post some minimal source code for the parser and the javascript/mochikit stuff soon, and if this problem is tractable it can become another example for ycr2js. A possible reason why this wouldn't work is that when you're using the ycr2js stuff, *everything* has to be generated; it doesn't play well plugging in an existing javascript function with a generated one. I'd be surprised if that was the case, but since I haven't actually successfully generated any code yet i guess anything possible. At any rate, if this sort of thing could cause issues please someone in the know give me fair warning. thomas.

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Re: [Haskell-cafe] New demo/test program for Yhc Javascript backend
by Thomas Hartman 26 Nov '07

26 Nov '07

2007/11/26, Dimitry Golubovsky <golubovsky(a)gmail.com>: > Thomas, > > All published examples (source, html) go into web/jsdemos subdirectory > (from the root of the Yhc repo source tree). right; it would be nice to have a makefile (or makefiles) there that works out of the box, rather than relying on the wiki http://haskell.org/haskellwiki/Yhc/Javascript/Users_guide#Building_and_inst… which, among other things, requires cleaning up tabs for the formatting to work. Even if it can't be incorporated into the buildbot, it would be nice to have some working make examples to orient one's self. Secondly, with regards to your cps changes, are you aware of *any* demos that will compile from head? I want to get going with this because I have a situation where ycr2js would be really useful for an in-house project, client side table filtering on large tables. Maybe I should say a bit about this as well so you can tell me if this seems realistic, I'll write a separate email about that. t. > > Not all of them may be compilable at the moment though (and some will > never be compilable in the future, just kept there for historic > reasons - that's why they are not being tested by the buildbot). > > I am currently going through transition from plain CPS to Cont monad, > so regular monadic notation can be used instead of CPS. However I am > experiencing memory leaks in MSIE (try the EchoM example) which I did > not expect to happen (never had them in plain CPS). If I cannot fix > that I'll roll back to plain CPS. > > On 11/26/07, Thomas Hartman <tphyahoo(a)gmail.com> wrote: > > It would be really helpful if you could include this (and other) > > examples in an /examples directory under > > > > src/translator/js > > > -- > Dimitry Golubovsky > > Anywhere on the Web >

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Re: getDirectoryContents still causing problems Re: problems building ycr2js (hopefully fixed)
by Thomas Hartman 26 Nov '07

26 Nov '07

Based on my experience, I wouldn't recommend doing scons fullclean; rather, I would darcs checkout and go from scratch. Annoying, but seems to work better. thomas. 2007/11/26, Dimitry Golubovsky <golubovsky(a)gmail.com>: > Thomas, > > This happens sometimes as Yhc depends on many other packages not very > well in sync (e. g. FilePath). Plus, internal dependencies are not > always tracked very well. Or binary core format gets upgraded (that > means, the core linker does not accept older versions of core files, > and all of them have to be regenerated). > > You may see sometimes recommendations in the Yhc mailing list: pull > patches, then do scons fullclean. Or re-check the whole repo out, > which is basically the same. > > Thanks. > > On 11/26/07, Thomas Hartman <tphyahoo(a)gmail.com> wrote: > > False alarm. > > > > I rm -rf ed yhhc, fresh darcs got the latest yhc, reinstalled yhc, and redid > > > > (cd src/translator/js; make all install) > > > > and it built. > > > > 2007/11/26, Dimitry Golubovsky <golubovsky(a)gmail.com>: > > > Thomas, > > > > > > It looks like this comes from Yhc, not from the Javascript backend. > > > > > > Have you done the full sequence of (starting with clean repo)? > > > > > > darcs get darcs.haskell.org/yhc > > > scons core=1 build > > > scons prefix=... install # whatever your stuff goes, and yhc will be > > > in bin/ from that, and this bin/ should be on your path > > > (cd src/translator/js; make all install) > > > > > > Please let me know where it fails. > > > > > > Thank you. > > > > > > On 11/26/07, Thomas Hartman <tphyahoo(a)gmail.com> wrote: > > > > still having problems darcs pulling your updates, related to System.FilePath. > > > > > > > > did you make clean and then make again? > > > > > > > > I darcs pulled everything. > > > > > > > > (cd src/translator/js; make all install) > > > > > > > > ... ... > > > > (cd /home/thartman/haskell-installs/yhc-install/yhc/src/translator/js/lib/haskell; > > > > \ > > > > for f in `find . -name '*.hs' | sort` ; do make -s -f > > > > /home/thartman/haskell-installs/yhc-install/yhc/src/translat\ > > > > or/js/Makefile `dirname $f`/`basename $f .hs`.ycr ; done) > > > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > > > getDirectoryContents: does not exist (No such fi\ > > > > le or directory) > > > > > > > > -s flag silences, we don't want that, with verbose output again we see > > > > that make is failing for a huge number of packages > > > > > > > > (cd /home/thartman/haskell-installs/yhc-install/yhc/src/translator/js/lib/h\ > > > > askell; \ > > > > for f in `find . -name '*.hs' | sort` ; do make -f > > > > /home/thartman/haskell-installs/yhc-install/yhc/src/translator/\ > > > > js/Makefile `dirname $f`/`basename $f .hs`.ycr ; done) > > > > > yhc --core --no-bytecode CDOM/Level1/DomUtils.hs > > > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > > > getDirectoryContents: does not exist (No such fi\ > > > > le or directory) > > > > > > > > make: *** [CDOM/Level1/DomUtils.ycr] Error 1 > > > > yhc --core --no-bytecode CDOM/Level1/Events.hs > > > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > > > getDirectoryContents: does not exist (No such fi\ > > > > le or directory) > > > > > > > > ... > > > > > > > > thartman@none:~/haskell-installs/yhc-install/yhc/src/translator/js/lib/haskell>yhc > > > > --core --no-bytecode CDOM/Level1/DomUtils\ > > > > .hs > > > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > > > getDirectoryContents: does not exist (No such fi\ > > > > le or directory) > > > > > > > > Unfamiliar with yhc, I couldn't figure out where getDirectory contents > > > > is being called from. > > > > > > > > Grepping at the root, I guess something here is causing problems > > > > > > > > thartman@none:~/haskell-installs/yhc-install/yhc>grep -irl > > > > getDirectoryContents * > > > > Make/Useful.hs > > > > inst/bin/yhc > > > > src/compiler98/Package.hs > > > > src/packages/yhc-base-1.0/System/Directory.hs > > > > src/packages/haskell98-1.0/Directory.hs > > > > src/tester/Main.hs > > > > tests/conformance98/Directory/getDirContents/Main.hs > > > > > > > > best, thomas. > > > > > > > > 2007/11/25, Dimitry Golubovsky <golubovsky(a)gmail.com>: > > > > > Thomas, > > > > > > > > > > On Nov 25, 2007 5:50 PM, Thomas Hartman <tphyahoo(a)gmail.com> wrote: > > > > > > Thanks Dmitri, I also had to fix an issue with System.FilePath, > > > > > > there's a message about this on haskell cafe. > > > > > > > > > > In fact, takeDirectory is the right replacement for getDirectory in > > > > > older FilePath. I have pushed this change too. > > > > > > > > > > Thanks. > > > > > > > > > > -- > > > > > Dimitry Golubovsky > > > > > > > > > > Anywhere on the Web > > > > > > > > > > > > > > > > > > -- > > > Dimitry Golubovsky > > > > > > Anywhere on the Web > > > > > > > > -- > Dimitry Golubovsky > > Anywhere on the Web >

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Re: getDirectoryContents still causing problems Re: problems building ycr2js (hopefully fixed)
by Thomas Hartman 26 Nov '07

26 Nov '07

False alarm. I rm -rf ed yhhc, fresh darcs got the latest yhc, reinstalled yhc, and redid (cd src/translator/js; make all install) and it built. 2007/11/26, Dimitry Golubovsky <golubovsky(a)gmail.com>: > Thomas, > > It looks like this comes from Yhc, not from the Javascript backend. > > Have you done the full sequence of (starting with clean repo)? > > darcs get darcs.haskell.org/yhc > scons core=1 build > scons prefix=... install # whatever your stuff goes, and yhc will be > in bin/ from that, and this bin/ should be on your path > (cd src/translator/js; make all install) > > Please let me know where it fails. > > Thank you. > > On 11/26/07, Thomas Hartman <tphyahoo(a)gmail.com> wrote: > > still having problems darcs pulling your updates, related to System.FilePath. > > > > did you make clean and then make again? > > > > I darcs pulled everything. > > > > (cd src/translator/js; make all install) > > > > ... ... > > (cd /home/thartman/haskell-installs/yhc-install/yhc/src/translator/js/lib/haskell; > > \ > > for f in `find . -name '*.hs' | sort` ; do make -s -f > > /home/thartman/haskell-installs/yhc-install/yhc/src/translat\ > > or/js/Makefile `dirname $f`/`basename $f .hs`.ycr ; done) > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > getDirectoryContents: does not exist (No such fi\ > > le or directory) > > > > -s flag silences, we don't want that, with verbose output again we see > > that make is failing for a huge number of packages > > > > (cd /home/thartman/haskell-installs/yhc-install/yhc/src/translator/js/lib/h\ > > askell; \ > > for f in `find . -name '*.hs' | sort` ; do make -f > > /home/thartman/haskell-installs/yhc-install/yhc/src/translator/\ > > js/Makefile `dirname $f`/`basename $f .hs`.ycr ; done) > > > yhc --core --no-bytecode CDOM/Level1/DomUtils.hs > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > getDirectoryContents: does not exist (No such fi\ > > le or directory) > > > > make: *** [CDOM/Level1/DomUtils.ycr] Error 1 > > yhc --core --no-bytecode CDOM/Level1/Events.hs > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > getDirectoryContents: does not exist (No such fi\ > > le or directory) > > > > ... > > > > thartman@none:~/haskell-installs/yhc-install/yhc/src/translator/js/lib/haskell>yhc > > --core --no-bytecode CDOM/Level1/DomUtils\ > > .hs > > yhc: /home/thartman/haskell-installs/yhc-install/yhc/inst/lib/yhc/packages: > > getDirectoryContents: does not exist (No such fi\ > > le or directory) > > > > Unfamiliar with yhc, I couldn't figure out where getDirectory contents > > is being called from. > > > > Grepping at the root, I guess something here is causing problems > > > > thartman@none:~/haskell-installs/yhc-install/yhc>grep -irl > > getDirectoryContents * > > Make/Useful.hs > > inst/bin/yhc > > src/compiler98/Package.hs > > src/packages/yhc-base-1.0/System/Directory.hs > > src/packages/haskell98-1.0/Directory.hs > > src/tester/Main.hs > > tests/conformance98/Directory/getDirContents/Main.hs > > > > best, thomas. > > > > 2007/11/25, Dimitry Golubovsky <golubovsky(a)gmail.com>: > > > Thomas, > > > > > > On Nov 25, 2007 5:50 PM, Thomas Hartman <tphyahoo(a)gmail.com> wrote: > > > > Thanks Dmitri, I also had to fix an issue with System.FilePath, > > > > there's a message about this on haskell cafe. > > > > > > In fact, takeDirectory is the right replacement for getDirectory in > > > older FilePath. I have pushed this change too. > > > > > > Thanks. > > > > > > -- > > > Dimitry Golubovsky > > > > > > Anywhere on the Web > > > > > > > > -- > Dimitry Golubovsky > > Anywhere on the Web >

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