December 2007 - Haskell-Cafe

regexen no go with 6.8.1?
by Jason Dusek 04 Dec '07

04 Dec '07

Is it just me, or are all the regex implementations broken with new change in lib layout for 6.8.1? Are fixes available in darcs? -- _jsn

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Leopard: ghc 6.8.1 and the case of the missing _environ
by Joel Reymont 04 Dec '07

04 Dec '07

Symptoms: You build 6.8.1 from source on Leopard (x86 in my case) and then junior:ghc-6.8.1 joelr$ ghci GHCi, version 6.8.1: http://www.haskell.org/ghc/ :? for help ghc-6.8.1: /usr/local/lib/ghc-6.8.1/lib/base-3.0.0.0/HSbase-3.0.0.0.o: unknown symbol `_environ' Loading package base ... linking ... ghc-6.8.1: unable to load package `base' Problem: ghc binaries are being stripped upon installation which eliminates _environ, e.g. junior:tmp joelr$ nm x|grep environ 00002ff0 T ___hscore_environ 0004d004 D _environ junior:tmp joelr$ strip x junior:tmp joelr$ nm x|grep environ Solution: Need to make sure install-sh does _not_ use the -s option. Haven't found out where this needs to be done yet. A temporary workaround is to ask Manuel for the pre-built binaries. Thanks, Joel -- http://wagerlabs.com

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Re: The Opposite of $
by Alan Hawkins 04 Dec '07

04 Dec '07

|> is not defined in the prelude but can be defined as let (|>) = flip ($) to make it the opposite of $ which means the syntax looks more like the Unix pipe '|' command eg. filter (\x-> x >3 && x < 7) $ [1..10] ++ [5] [1..10] ++ [5] |> filter (\x-> x >3 && x < 7) res: [4,5,6] note that with the |> the function applications are read as naturally left to right as apposed to the $ which reads left to right. a style more in line with the syntax f (x) ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs

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The Opposite of $
by PR Stanley 04 Dec '07

04 Dec '07

Hi According to the Haskell Wikibook the is the opposite of $. The text also oints out that the "|>" can be used as a substitute. I tried using |> but to no avail. Is the list au fait with the |> operator? Thanks, Paul

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Fw: [Haskell-cafe] Re: do
by Thomas Hartman 03 Dec '07

03 Dec '07

It took me forever to get comfortable with monads. I think it helps if you've seen continuations, or done FP before, or a variety of things that build familiarity. But probably the only thing that I think will work for the masses of plodders (there are always a few stars to crash the curve) is a desire to learn and tons of practice. I wouldn't worry so much about the ideal way to introduce the material. Oh, one other thing. You learn monads when you need them. You need IO right away... well, after you tired of playing with pure functions in the ghci sandbox. my 2c. t. "Dan Piponi" <dpiponi(a)gmail.com> Sent by: haskell-cafe-bounces(a)haskell.org 12/03/2007 07:19 PM To haskell-cafe(a)haskell.org cc Subject Re: [Haskell-cafe] Re: do On Dec 3, 2007 3:54 PM, Ben Franksen <ben.franksen(a)online.de> wrote: > I don't buy this. As has been noted by others before, IO is a very special > case, in that it can't be defined in Haskell itself, and there is no > evaluation function runIO :: IO a -> a. I'm not sure what a function of type m a -> a has to do with the concept of a monad. And I don't really see what the problem is with the IO monad not being definable in (pure) Haskell. IO exposes the same interface as every other Monad, and you need to use that interface to get visible results. So people have to learn it whatever. And the whole point of the Monad is that it's an interface, not a specific implementation. > I'd rather use a simple example like Maybe (modeling failure as an effect). And I'd like to see more people getting off the ground doing interesting stuff with Haskell before their attention spans for pointless-seeming new stuff run out. I'm not talking about the smartest people in computer science courses here. I'm talking about the millions of people writing everyday Python and Ruby scripts, say, who might benefit from a more expressive, type-safe, well-thought out, fast and compiled language. -- Dan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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doing builds using cygwin on Windows
by Galchin Vasili 03 Dec '07

03 Dec '07

To Nanonthief ...... VasiliIGalchin wrote: > > > " .. however, I don't see in which file PATH can be set. Any help? I > really > want to get my Haskell build environment set up and cranking away. > Unless I misunderstood what you want, you can add a path to the PATH variable by adding the line: export PATH="$PATH:/path/to/folder" to the ~/.bashrc file (and also possibly the ~/.bash_profile file). I've also tried to build haskell with cygwin, but didn't have any luck. Could you describe how you managed to do it? -- nanothief ... here is what I decided to add to unix.cabal .. and I am getting farther ... build-depends: base, directory extensions: CPP, ForeignFunctionInterface include-dirs: include c:/cygwin/usr/include <<< added cygwin include path includes: HsUnix.h execvpe.h install-includes: HsUnix.h HsUnixConfig.h execvpe.h c-sources: cbits/HsUnix.c cbits/execvpe.c

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Possible Improvements
by PR Stanley 03 Dec '07

03 Dec '07

Hi data Tree = Leaf Int | Node Tree Int Tree occurs :: Int -> Tree -> Bool occurs m (Leaf n) = m == n occurs m (Node l n r) = m == n || occurs m l || occurs m r It works but I'd like to know if it can be improved in any way. Thanks, Paul

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Monads
by PR Stanley 03 Dec '07

03 Dec '07

Hi Does the list consider http://en.wikibooks.org/w/index.php?title=Haskell/Understanding_monads&oldi… a reliable tutorial on monads and, if not, could you recommend an onlien alternative please? Thanks, Paul

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ANN: atom 2007.12
by Tom Hawkins 03 Dec '07

03 Dec '07

Hello, Atom is a language embedded in Haskell for describing reactive software, primarily for realtime control applications. Based on conditional term rewriting, an atom description is composed of a set of state transition rules. The name "atom" comes from the atomic behavior of rules: if a rule is selected to fire, all its transitions occur or none at all. A hallmark of the language, rule atomicity greatly simplifies design reasoning. This release of atom is a major redirection. Atom is no longer a hardware description language (I changed jobs. I'm now in software.). Much of the frontend language and backend generators have changed, though rule scheduling remains nearly the same. On the frontend, atom's Signal datatypes have been replaced with Terms and Vars, which leverage Haskell's GADTs. The 4 supported Term and Var types include Bool, Int, Float, and Double. At the backend, atom generates C and Simulink models. The Verilog and VHDL generators have been dropped, but they may reappear in the future. Enjoy! http://funhdl.org/ darcs get http://funhdl.org/darcs/atom -Tom

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A tale of three shootout entries
by Sterling Clover 03 Dec '07

03 Dec '07

In some spare time over the holidays I cooked up three shootout entries, for Fasta, the Meteor Contest, and Reverse Complement. I should probably have tossed them to haskell-cafe before submission, for review and ideas, but they're up now. In any case, all three were great learning experiences, but could use some other eyes and ideas to be the best that they can. First up is the meteor-contest entry. http://shootout.alioth.debian.org/gp4/benchmark.php? test=meteor&lang=ghc&id=5 This is the clear win of the bunch, with significantly improved time thanks to its translation of the better algorithm from Clean. However, it's still missing something. Nearly all its time is spent in a tight loop in the solveCell function near the end of the code. I tried unboxing this, but failed because it spends the bulk of its time applying a bitwise and between the recursively passed value and a piece of data retrieved from the masksAtCell data structure which is of type :: Array (Row,Col) (Array Color [Mask]). (Note that Mask, Color, Row and Col are all type synonyms for Int that I added for readability). As each Mask is stored in this list, the masks can't easily be unboxed -- some sort of custom data structure built using the FFI seems in order here. If anyone wants to tackle this, I think it could be a big win for performance. Next is reverse-complement. http://shootout.alioth.debian.org/gp4/benchmark.php? test=revcomp&lang=ghc&id=3 This *would* be a big win except I dimly doubled memory usage from the previous entry due to filtering newlines explicitly -- which does, one should note, provide a large performance gain. The solution here seems the most obvious -- roll the newline stripping into the destructive modifications performed in the revcomp function, as the winning C++ entry does. I'll probably get around to this eventually, but if someone else wants to try to implement this or any other performance improvements, please jump right in. Additionally, there might be some other tricks to reducing its memory usage that escape me at the moment (noting, of course, that using a strict bytestring, as we should, its unavoidable that we consume the entire contents of the input at once... I think?) Finally, there's fasta. http://shootout.alioth.debian.org/gp4/benchmark.php? test=fasta&lang=ghc&id=2 This one really depresses me. It outperforms the previous version by roughly 20% on my machine (PPC) but underperforms by roughly the same amount on the shootout box. If you compare it to dons previous version, the "optimizations" I attempted should be pretty obvious. First, I precompute the partial sums for the frequency tables and alter the choose function accordingly. This is a pretty basic measure that all the better entries seem to do. Next, I unboxed the random function, which yielded big speedups However, given that we use an unfoldN, as we should, I couldn't very well pass it a function that returned something of kind #, (especially as Maybe, which unfoldN uses, is of kind *->*). Thus, I hid the unrolled loop in a lazy list of floats that is passed instead of a random seed. I suspect that for some reason I don't understand relating to differences in processors, GHC's internal handling of floating point math, or who knows what, this somehow is the source of the slowdown. If someone with an Intel Pentium 4 machine comparable to that of the shootout box wants to take a look at this code and see why it underperforms, I'd be much obliged. It really seems to me that GHC's fasta performance is far below where it should be (4x slower than Java!) , and I'd like to get its numbers up somehow. Thanks, Sterl p.s. It looks like they've depreciated chameneos in favor of a new version, chameneos-redux. As this was one of the places Haskell really rocked the competition, it would probably be worth updating the Haskell entry for the new benchmark. Also, the n-bodies benchmark seems like another that could be much improved.

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