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Applying a Dynamic function to a container of Dynamics
by Alfonso Acosta 21 Dec '07

21 Dec '07

Hi all, dynApp allows to apply a Dynamic function to a Dynamic argument: dynApp :: Dynamic -> Dynamic -> Dynamic I don't seem to find a way (without modifying Data.Dynamic itself) to code this function import Data.Typeable import Data.Dynamic import Data.Foldable dynApp1 :: (Typeable1 container, Foldable container) => Dynamic -> container Dynamic -> Dynamic dynApp1 f -- originally of type :: container a -> b val --- all its values _must_ have type :: b -- I get stuck when trying to transform val to type Dynamic (transform :: container Dynamic -> Dynamic) in order to apply f nor even the more concrete case of lists dynAppList :: Dynamic -> [Dynamic] -> Dynamic Any suggestions? Thanks, Fons

1 0

Smart Constructor Puzzle
by Ronald Guida 21 Dec '07

21 Dec '07

I'm playing around with smart constructors, and I have encountered a weird puzzle. My goal is to do vector arithmetic. I'm using smart constructors so that I can store a vector as a list and use the type system to staticly enforce the length of a vector. So my first step is to define Peano numbers at the type level. > data PZero = PZero deriving (Show) > data PSucc a = PSucc a deriving (Show) > > type P1 = PSucc PZero > type P2 = PSucc P1 > type P3 = PSucc P2 > -- etc Next, I define a vector type and tag it with a Peano number. > data Vec s t = Vec [t] deriving (Eq, Ord, Show, Read) Now I can define a few smart constructors. > vec0 :: Vec PZero t > vec0 = Vec [] > > vec1 :: t -> Vec P1 t > vec1 x = Vec [x] > > vec2 :: t -> t -> Vec P2 t > vec2 x y = Vec [x, y] > > vec3 :: t -> t -> t -> Vec P3 t > vec3 x y z = Vec [x, y, z] Now here's the puzzle. I want to create a function "vecLength" that accepts a vector and returns its length. The catch is that I want to calculate the length based on the /type/ of the vector, without looking at the number of elements in the list. So I started by defining a class that allows me to convert a Peano number to an integer. I couldn't figure out how to define a function that converts the type directly to an integer, so I am using a two-step process. Given a Peano type /t/, I would use the expression "pToInt (pGetValue :: t)". > class Peano t where > pGetValue :: t > pToInt :: t -> Int > > instance Peano PZero where > pGetValue = PZero > pToInt _ = 0 > > instance (Peano t) => Peano (PSucc t) where > pGetValue = PSucc pGetValue > pToInt (PSucc a) = 1 + pToInt a Finally, I tried to define vecLength, but I am getting an error. > vecLength :: (Peano s) => Vec s t -> Int > vecLength _ = pToInt (pGetValue :: s) < Could not deduce (Peano s1) from the context () < arising from a use of `pGetValue' < Possible fix: < add (Peano s1) to the context of the polymorphic type `forall s. s' < In the first argument of `pToInt', namely `(pGetValue :: s)' < In the expression: pToInt (pGetValue :: s) < In the definition of `vecLength': < vecLength _ = pToInt (pGetValue :: s) Any suggestions? -- Ron

5 4

upgrading regex in GHC 6.8.2
by Michael Mounteney 21 Dec '07

21 Dec '07

Hello, I have an application that uses/used Text.Regex and have just updated GHC from 6.6.1 to 6.8.2 and it seems that Text.Regex is gone, so I'm trying to install the replacement from Hackage. First of all, the procedure is quite tedious as one has to install the hierarchy of dependencies manually but apparently there are moves to automate this process. The procedure stalled on regex-base-0.92. I fixed the build-depends in regex-base.cabal to: Build-Depends: base >= 2.0, mtl, containers >= 0.1.0.1, bytestring, array following information I found via an internet search but on runghc Setup.hs install it says: Setup.hs: Error: Could not find module: Text.Regex.Base with any suffix: ["hi"] It seems that it is necessary to remove the Text.Regex.Base and Text.Regex.Base.Impl entries from the Exposed-Modules: line but then regex-posix build complains that it can't find Text.Regex.Base. I tried various hackery like compiling Text/Regex/Base.hs manually but even when Text/Regex/Base.hi exists, the runghc Setup.hs install error message above still occurs. What is happening ? -- _________________________________ Michael Mounteney,+618 4311 11547

3 2

Is there some place where I can find the hs-curses doc ?
by david48 21 Dec '07

21 Dec '07

It seems I can't find it. David.

3 3

instance Monad Either?
by Eric 21 Dec '07

21 Dec '07

According to this <http://www.randomhacks.net/articles/2007/03/10/haskell-8-ways-to-report-err…> Either is an instance of class Monad, but when I try to use the do notation I get a compiler error. What's going on? E.

4 4

[RFC] Preliminary benchmark graphs
by Peter Lund 21 Dec '07

21 Dec '07

I added Don's three benchmarks and redid all my benchmarks with: ghc 6.6.1 ghc 6.8.2 ghc 6.8.2 + bytestring 0.9.0.2 ghc 6.9.20071119 ghc 6.9.20071119 + bytestring 0.9.0.2 ghc head-as-of-yesterday-around-noon ghc head-as-of-yesterday-around-noon + bytestring 0.9.0.2 I tried to get the draft emails with intro, methodology, discussion, and conclusion completed yesterday but my brain simply wasn't up to it. Unfortunately, it still isn't quite up to it :( Since the perfect is the enemy of the good, I'll post the graphs for all the above 7 runs now. The rest will be forthcoming when I can think straight again, hopefully some time in the evening. I have scripts to help me install precisely the ghc version I want (and to make it easy to duplicate my results). I also have scripts to run the benchmarks, get correct memory measurements (-sstderr doesn't seem trustworthy), check the validity of each timing measurement, generate I/O traces, generate reports, and finally merging reports from different runs with or without rescaling. This attached report uses rescaling since I'm compiling different compiler/library combinations on the same machine. One thing that shows up very clearly in the graphs is that the memory situation is bad and that Don's recent fix only really solves the problem on 6.8.2, not on head. Another thing is that the backend really lets us down. I have hand-tweaked a simple byte counting benchmark and a simple space counting benchmark through increasing degrees of refinement from the banal to the heroic and timed those, too. It seems like improved register use alone would halve the run time. Add a sprinkling of MMX heroics and things get even better (but that's not realistic or even a good idea at the moment). The reason why lazy bytestrings perform so badly, speed-wise, is most likely a backend that doesn't do hoisting of "bounds checks" out of loops. -Peter charybdis ghc 6.6.1 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.8.2 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.8.2 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX=-bs0.9.0.2 charybdis ghc 6.9.20071119 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.9.20071119 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX=-bs0.9.0.2 charybdis ghc 6.9.20071217 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.9.20071217 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX=-bs0.9.0.2 Time (byte counting) std -------------------- avg dev slack hs/byte-bs----acc: 1.020 40‰ 0.0 █████▏ | -- 0.703 5‰ 0.4 ███▌ | -- 0.702 7‰ 0.3 ███▌ | -- 0.705 7‰ 0.1 ███▋ | -- 0.712 3‰ 0.1 ███▋ | -- 0.706 7‰ 0.1 ███▋ | -- 0.707 7‰ 0.9 ███▋ | hs/byte-bs----foldlx: 0.789 3‰ 0.3 ████ | -- 0.993 2‰ 0.2 █████ | -- 1.102 1‰ 0.2 █████▋ | -- 1.002 1‰ 0.5 █████▏ | -- 1.112 1‰ 0.3 █████▋ | -- 1.024 2‰ 0.2 █████▏ | -- 1.111 1‰ 0.1 █████▋ | hs/byte-bs----foldrx: 0.813 3‰ 0.1 ████▏ | -- 1.102 2‰ 0.3 █████▋ | -- 1.100 1‰ 0.1 █████▋ | -- 1.112 2‰ 0.1 █████▋ | -- 1.114 1‰ 0.4 █████▋ | -- 1.113 2‰ 0.5 █████▋ | -- 1.112 1‰ 0.2 █████▋ | hs/byte-bsl---acc: 3.599 13‰ 0.0 ██████████████████▎ | -- 2.609 17‰ 0.0 █████████████▎ | -- 2.560 15‰ 0.1 █████████████ | -- 2.595 14‰ 0.1 █████████████▏ | -- 2.574 16‰ 0.1 █████████████ | -- 2.613 12‰ 0.2 █████████████▎ | -- 2.656 44‰ 0.1 █████████████▌ | hs/byte-xxxxx-acc-1: 4.606 5‰ 0.0 ███████████████████████▍ | -- 4.730 3‰ 0.0 ████████████████████████ | -- 4.722 3‰ 0.1 ███████████████████████▉ | -- 4.436 5‰ 0.0 ██████████████████████▌ | -- 4.500 6‰ 0.1 ██████████████████████▊ | -- 4.462 4‰ 0.1 ██████████████████████▋ | -- 4.499 7‰ 0.1 ██████████████████████▊ | hs/byte-xxxxx-acc-2: 4.595 5‰ 0.0 ███████████████████████▎ | -- 4.704 1‰ 0.0 ███████████████████████▉ | -- 4.722 6‰ 0.0 ███████████████████████▉ | -- 4.473 8‰ 0.0 ██████████████████████▋ | -- 4.493 5‰ 0.0 ██████████████████████▊ | -- 4.477 3‰ 0.1 ██████████████████████▋ | -- 4.446 2‰ 0.0 ██████████████████████▌ | hs/byte-xxxxx-foldl: 4.566 9‰ 0.0 ███████████████████████▏ | -- 4.754 6‰ 0.1 ████████████████████████▏ | -- 4.735 7‰ 0.0 ████████████████████████ | -- 4.412 10‰ 0.0 ██████████████████████▍ | -- 4.486 3‰ 0.0 ██████████████████████▊ | -- 4.473 3‰ 0.0 ██████████████████████▋ | -- 4.511 10‰ 0.1 ██████████████████████▉ | Memory: Peak ------- KB hs/byte-bs----acc: 147448 ████████████████████████████████████████ | -- 147500 ████████████████████████████████████████ | -- 147616 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | -- 147732 ████████████████████████████████████████ | -- 147772 ████████████████████████████████████████ | -- 147780 ████████████████████████████████████████ | hs/byte-bs----foldlx: 147468 ████████████████████████████████████████ | -- 147528 ████████████████████████████████████████ | -- 147624 ████████████████████████████████████████ | -- 147748 ████████████████████████████████████████ | -- 147736 ████████████████████████████████████████ | -- 147796 ████████████████████████████████████████▏ | -- 147780 ████████████████████████████████████████ | hs/byte-bs----foldrx: 147452 ████████████████████████████████████████ | -- 147500 ████████████████████████████████████████ | -- 147624 ████████████████████████████████████████ | -- 147744 ████████████████████████████████████████ | -- 147740 ████████████████████████████████████████ | -- 147772 ████████████████████████████████████████ | -- 147784 ████████████████████████████████████████ | hs/byte-bsl---acc: 2872 ▊ | -- 2920 ▊ | -- 3040 ▉ | -- 3172 ▉ | -- 3184 ▉ | -- 3212 ▉ | -- 3216 ▉ | hs/byte-xxxxx-acc-1: 1572 ▍ | -- 1632 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1900 ▌ | hs/byte-xxxxx-acc-2: 1568 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1900 ▌ | -- 1896 ▌ | hs/byte-xxxxx-foldl: 1572 ▍ | -- 1632 ▌ | -- 1636 ▌ | -- 1900 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1896 ▌ | Time (space counting) std --------------------- avg dev slack hs/space-bs-c8-acc-1: 1.287 20‰ 0.2 ██████▌ | -- 1.131 2‰ 0.1 █████▊ | -- 1.132 2‰ 0.3 █████▊ | -- 1.145 1‰ 0.2 █████▊ | -- 1.150 1‰ 0.2 █████▉ | -- 1.147 2‰ 0.1 █████▊ | -- 1.147 2‰ 0.2 █████▊ | hs/space-bs-c8-count: 0.770 2‰ 0.0 ███▉ | -- 0.711 1‰ 0.4 ███▋ | -- 0.513 2‰ 0.2 ██▋ | -- 0.521 1‰ 0.2 ██▋ | -- 0.523 3‰ 0.2 ██▋ | -- 0.522 5‰ 0.2 ██▋ | -- 0.523 3‰ 0.6 ██▋ | hs/space-bs-c8-foldlx-1: 1.272 1‰ 0.2 ██████▌ | -- 1.205 2‰ 0.2 ██████▏ | -- 1.164 3‰ 0.0 █████▉ | -- 1.221 1‰ 0.1 ██████▏ | -- 1.176 1‰ 0.3 ██████ | -- 1.259 1‰ 0.1 ██████▍ | -- 1.176 1‰ 0.2 ██████ | hs/space-bs-c8-foldlx-2: 1.270 1‰ 0.2 ██████▍ | -- 1.207 1‰ 0.2 ██████▏ | -- 1.165 2‰ 0.1 █████▉ | -- 1.219 2‰ 0.2 ██████▏ | -- 1.176 1‰ 0.3 ██████ | -- 1.258 1‰ 0.2 ██████▍ | -- 1.177 1‰ 0.2 ██████ | hs/space-bs-c8-foldrx: 1.064 2‰ 0.1 █████▍ | -- 1.168 2‰ 0.2 █████▉ | -- 1.164 1‰ 0.3 █████▉ | -- 1.172 2‰ 0.3 █████▉ | -- 1.177 1‰ 0.2 ██████ | -- 1.176 1‰ 0.2 ██████ | -- 1.176 1‰ 0.1 ██████ | hs/space-bs-c8-lenfil: 1.271 1‰ 0.1 ██████▍ | -- 1.218 1‰ 0.2 ██████▏ | -- 0.541 3‰ 0.2 ██▊ | -- 1.223 1‰ 0.2 ██████▎ | -- 0.549 1‰ 0.4 ██▊ | -- 1.225 1‰ 0.2 ██████▎ | -- 0.551 5‰ 0.4 ██▊ | hs/space-bslc8-acc-1: 6.367 17‰ 0.2 ████████████████████████████████▎ | -- 3.396 7‰ 0.1 █████████████████▎ | -- 3.508 4‰ 0.1 █████████████████▊ | -- 3.388 10‰ 0.1 █████████████████▏ | -- 3.441 10‰ 0.1 █████████████████▍ | -- 3.438 3‰ 0.0 █████████████████▍ | -- 3.434 13‰ 0.1 █████████████████▍ | hs/space-bslc8-acc-2: 6.150 21‰ 0.0 ███████████████████████████████▏ | -- 3.470 5‰ 0.0 █████████████████▋ | -- 3.439 10‰ 0.1 █████████████████▍ | -- 3.386 5‰ 0.1 █████████████████▏ | -- 3.479 11‰ 0.1 █████████████████▋ | -- 3.467 6‰ 0.1 █████████████████▌ | -- 3.470 10‰ 0.1 █████████████████▋ | hs/space-bslc8-acc-3: 4.041 21‰ 0.1 ████████████████████▌ | -- 2.959 13‰ 0.0 ███████████████ | -- 2.920 16‰ 0.1 ██████████████▊ | -- 2.832 4‰ 0.1 ██████████████▍ | -- 2.925 14‰ 0.1 ██████████████▊ | -- 2.987 9‰ 0.0 ███████████████▏ | -- 2.996 20‰ 0.1 ███████████████▏ | hs/space-bslc8-count: 0.713 1‰ 0.3 ███▋ | -- 0.735 1‰ 0.4 ███▊ | -- 0.431 0‰ 0.7 ██▏ | -- 0.477 2‰ 0.4 ██▍ | -- 0.482 1‰ 0.4 ██▌ | -- 0.479 1‰ 0.6 ██▍ | -- 0.482 2‰ 0.4 ██▌ | hs/space-bslc8-foldl: 1.431 1‰ 0.3 ███████▎ | -- 1.398 1‰ 0.2 ███████▏ | -- 1.197 1‰ 0.2 ██████ | -- 1.458 1‰ 0.3 ███████▍ | -- 1.059 0‰ 0.0 █████▍ | -- 1.459 1‰ 0.1 ███████▍ | -- 1.061 0‰ 0.4 █████▍ | hs/space-bslc8-foldlx-1: 1.430 1‰ 0.1 ███████▎ | -- 1.400 1‰ 0.1 ███████▏ | -- 1.197 1‰ 0.0 ██████ | -- 1.458 0‰ 0.1 ███████▍ | -- 1.060 1‰ 0.0 █████▍ | -- 1.457 1‰ 0.1 ███████▍ | -- 1.060 1‰ 0.2 █████▍ | hs/space-bslc8-foldlx-2: 1.431 1‰ 0.1 ███████▎ | -- 1.399 1‰ 0.1 ███████▏ | -- 1.196 1‰ 0.1 ██████ | -- 1.457 1‰ 0.1 ███████▍ | -- 1.060 1‰ 0.3 █████▍ | -- 1.458 1‰ 0.1 ███████▍ | -- 1.060 1‰ 0.0 █████▍ | hs/space-bslc8-foldr-1: 1.748 1‰ 0.0 ████████▉ | -- 1.579 2‰ 0.1 ████████ | -- 1.220 2‰ 0.2 ██████▏ | -- 1.312 1‰ 0.2 ██████▋ | -- 1.213 1‰ 0.2 ██████▏ | -- 1.325 4‰ 0.2 ██████▊ | -- 1.213 2‰ 0.2 ██████▏ | hs/space-bslc8-foldr-2: 1.745 1‰ 0.1 ████████▉ | -- 1.579 2‰ 0.1 ████████ | -- 1.220 1‰ 0.2 ██████▏ | -- 1.315 1‰ 0.2 ██████▋ | -- 1.210 1‰ 0.2 ██████▏ | -- 1.317 4‰ 0.2 ██████▋ | -- 1.213 2‰ 0.2 ██████▏ | hs/space-bslc8-lenfil-1: 1.521 7‰ 0.2 ███████▊ | -- 1.295 1‰ 0.2 ██████▌ | -- 0.429 0‰ 0.2 ██▏ | -- 1.323 1‰ 0.1 ██████▊ | -- 0.483 2‰ 0.4 ██▌ | -- 1.327 1‰ 0.2 ██████▊ | -- 0.482 2‰ 0.4 ██▌ | hs/space-bslc8-lenfil-2: 1.532 6‰ 0.1 ███████▊ | -- 1.296 0‰ 0.0 ██████▌ | -- 0.429 0‰ 0.2 ██▏ | -- 1.325 1‰ 0.1 ██████▊ | -- 0.483 1‰ 0.6 ██▌ | -- 1.327 1‰ 0.2 ██████▊ | -- 0.482 2‰ 0.4 ██▌ | hs/space-bsl---foldlx: 1.288 1‰ 0.2 ██████▌ | -- 1.333 1‰ 0.0 ██████▊ | -- 1.168 1‰ 0.2 █████▉ | -- 1.391 1‰ 0.1 ███████ | -- 1.006 1‰ 0.3 █████▏ | -- 1.395 1‰ 0.1 ███████▏ | -- 1.008 1‰ 0.2 █████▏ | hs/space-xxxxx-acc-1: 5.036 7‰ 0.1 █████████████████████████▌ | -- 5.381 6‰ 0.0 ███████████████████████████▎ | -- 5.358 8‰ 0.1 ███████████████████████████▏ | -- 4.991 1‰ 0.1 █████████████████████████▎ | -- 5.047 7‰ 0.1 █████████████████████████▌ | -- 5.051 3‰ 0.1 █████████████████████████▋ | -- 5.049 4‰ 0.1 █████████████████████████▋ | hs/space-xxxxx-acc-2: 5.009 7‰ 0.1 █████████████████████████▍ | -- 5.437 4‰ 0.1 ███████████████████████████▌ | -- 5.406 2‰ 0.0 ███████████████████████████▍ | -- 4.985 1‰ 0.0 █████████████████████████▎ | -- 5.057 4‰ 0.1 █████████████████████████▋ | -- 5.048 6‰ 0.1 █████████████████████████▌ | -- 5.089 6‰ 0.0 █████████████████████████▊ | hs/space-xxxxx-foldl: 5.024 5‰ 0.0 █████████████████████████▌ | -- 5.371 9‰ 0.0 ███████████████████████████▎ | -- 5.301 9‰ 0.1 ██████████████████████████▉ | -- 5.035 2‰ 0.1 █████████████████████████▌ | -- 5.037 3‰ 0.0 █████████████████████████▌ | -- 5.046 4‰ 0.0 █████████████████████████▌ | -- 5.042 4‰ 0.0 █████████████████████████▌ | hs/space-xxxxx-lenfil: 7.042 4‰ 0.0 ███████████████████████████████████▋ | -- 7.505 3‰ 0.0 ██████████████████████████████████████| -- 7.498 3‰ 0.0 ██████████████████████████████████████| -- 7.106 8‰ 0.1 ████████████████████████████████████ | -- 7.092 3‰ 0.1 ███████████████████████████████████▉ | -- 7.083 3‰ 0.0 ███████████████████████████████████▉ | -- 7.121 5‰ 0.1 ████████████████████████████████████ | hs/space-bslc8-chunk-1: n/a -- 1.054 0‰ 0.3 █████▍ | -- 1.053 1‰ 0.1 █████▍ | -- 1.094 0‰ 0.3 █████▌ | -- 1.088 0‰ 0.0 █████▌ | -- 1.096 1‰ 0.1 █████▌ | -- 1.089 0‰ 0.6 █████▌ | hs/space-bslc8-chunk-2: n/a -- 1.055 0‰ 0.3 █████▍ | -- 1.053 0‰ 0.1 █████▍ | -- 1.094 1‰ 0.3 █████▌ | -- 1.088 1‰ 0.2 █████▌ | -- 1.096 1‰ 0.2 █████▌ | -- 1.089 0‰ 0.1 █████▌ | hs/space-bslc8-chunk-3: n/a -- 1.190 4‰ 0.2 ██████ | -- 1.199 1‰ 0.3 ██████▏ | -- 1.087 1‰ 0.3 █████▌ | -- 1.051 1‰ 0.4 █████▍ | -- 1.077 1‰ 0.1 █████▌ | -- 1.053 1‰ 0.2 █████▍ | hs/space-bslc8-chunk-4: n/a -- 1.054 0‰ 0.2 █████▍ | -- 1.054 0‰ 0.2 █████▍ | -- 1.099 0‰ 0.3 █████▋ | -- 1.097 1‰ 0.1 █████▌ | -- 1.094 1‰ 0.2 █████▌ | -- 1.096 0‰ 0.0 █████▌ | Memory: Peak ------- KB hs/space-bs-c8-acc-1: 147448 ████████████████████████████████████████ | -- 147492 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147736 ████████████████████████████████████████ | -- 147740 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | hs/space-bs-c8-count: 147448 ████████████████████████████████████████ | -- 147500 ████████████████████████████████████████ | -- 147612 ████████████████████████████████████████ | -- 147744 ████████████████████████████████████████ | -- 147756 ████████████████████████████████████████ | -- 147764 ████████████████████████████████████████ | -- 147776 ████████████████████████████████████████ | hs/space-bs-c8-foldlx-1: 147468 ████████████████████████████████████████ | -- 147524 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147756 ████████████████████████████████████████ | -- 147744 ████████████████████████████████████████ | -- 147796 ████████████████████████████████████████▏ | -- 147752 ████████████████████████████████████████ | hs/space-bs-c8-foldlx-2: 147468 ████████████████████████████████████████ | -- 147520 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | -- 147748 ████████████████████████████████████████ | -- 147796 ████████████████████████████████████████▏ | -- 147756 ████████████████████████████████████████ | hs/space-bs-c8-foldrx: 147448 ████████████████████████████████████████ | -- 147496 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147732 ████████████████████████████████████████ | -- 147748 ████████████████████████████████████████ | -- 147760 ████████████████████████████████████████ | -- 147756 ████████████████████████████████████████ | hs/space-bs-c8-lenfil: 147464 ████████████████████████████████████████ | -- 147524 ████████████████████████████████████████ | -- 167176 █████████████████████████████████████████████▍| -- 147756 ████████████████████████████████████████ | -- 167300 █████████████████████████████████████████████▍| -- 147788 ████████████████████████████████████████ | -- 167320 █████████████████████████████████████████████▍| hs/space-bslc8-acc-1: 2872 ▊ | -- 2920 ▊ | -- 3048 ▉ | -- 3192 ▉ | -- 3228 ▉ | -- 3180 ▉ | -- 3196 ▉ | hs/space-bslc8-acc-2: 2872 ▊ | -- 2924 ▊ | -- 3048 ▉ | -- 3192 ▉ | -- 3228 ▉ | -- 3180 ▉ | -- 3200 ▉ | hs/space-bslc8-acc-3: 2868 ▊ | -- 2924 ▊ | -- 3052 ▉ | -- 3196 ▉ | -- 3232 ▉ | -- 3172 ▉ | -- 3208 ▉ | hs/space-bslc8-count: 1476 ▍ | -- 1520 ▍ | -- 1656 ▌ | -- 79204 █████████████████████▌ | -- 82248 ██████████████████████▎ | -- 79220 █████████████████████▌ | -- 82224 ██████████████████████▎ | hs/space-bslc8-foldl: 1552 ▍ | -- 1620 ▌ | -- 1632 ▌ | -- 85868 ███████████████████████▎ | -- 79224 █████████████████████▌ | -- 85852 ███████████████████████▎ | -- 79196 █████████████████████▌ | hs/space-bslc8-foldlx-1: 1556 ▍ | -- 1620 ▌ | -- 1636 ▌ | -- 85864 ███████████████████████▎ | -- 79224 █████████████████████▌ | -- 85852 ███████████████████████▎ | -- 79196 █████████████████████▌ | hs/space-bslc8-foldlx-2: 1552 ▍ | -- 1616 ▌ | -- 1636 ▌ | -- 85868 ███████████████████████▎ | -- 79224 █████████████████████▌ | -- 85852 ███████████████████████▎ | -- 79196 █████████████████████▌ | hs/space-bslc8-foldr-1: 169480 ██████████████████████████████████████████████| -- 169544 ██████████████████████████████████████████████| -- 149076 ████████████████████████████████████████▍ | -- 169700 ██████████████████████████████████████████████| -- 149704 ████████████████████████████████████████▋ | -- 169680 ██████████████████████████████████████████████| -- 149680 ████████████████████████████████████████▋ | hs/space-bslc8-foldr-2: 169480 ██████████████████████████████████████████████| -- 169544 ██████████████████████████████████████████████| -- 149076 ████████████████████████████████████████▍ | -- 169700 ██████████████████████████████████████████████| -- 149708 ████████████████████████████████████████▋ | -- 169676 ██████████████████████████████████████████████| -- 149676 ████████████████████████████████████████▋ | hs/space-bslc8-lenfil-1: 38632 ██████████▌ | -- 38644 ██████████▌ | -- 1940 ▌ | -- 109404 █████████████████████████████▋ | -- 82324 ██████████████████████▍ | -- 109388 █████████████████████████████▋ | -- 82304 ██████████████████████▎ | hs/space-bslc8-lenfil-2: 38628 ██████████▌ | -- 38648 ██████████▌ | -- 1940 ▌ | -- 109404 █████████████████████████████▋ | -- 82328 ██████████████████████▍ | -- 109392 █████████████████████████████▋ | -- 82300 ██████████████████████▎ | hs/space-bsl---foldlx: 1560 ▍ | -- 1616 ▌ | -- 1620 ▌ | -- 85836 ███████████████████████▎ | -- 79184 █████████████████████▌ | -- 85864 ███████████████████████▎ | -- 79208 █████████████████████▌ | hs/space-xxxxx-acc-1: 1568 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1904 ▌ | hs/space-xxxxx-acc-2: 1572 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1904 ▌ | -- 1900 ▌ | hs/space-xxxxx-foldl: 1572 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1900 ▌ | -- 1904 ▌ | -- 1904 ▌ | -- 1904 ▌ | hs/space-xxxxx-lenfil: 1556 ▍ | -- 1608 ▍ | -- 1604 ▍ | -- 1892 ▌ | -- 1892 ▌ | -- 1888 ▌ | -- 1888 ▌ | hs/space-bslc8-chunk-1: n/a -- 1512 ▍ | -- 1636 ▌ | -- 65192 █████████████████▋ | -- 66216 ██████████████████ | -- 65204 █████████████████▋ | -- 66224 ██████████████████ | hs/space-bslc8-chunk-2: n/a -- 1512 ▍ | -- 1640 ▌ | -- 65192 █████████████████▋ | -- 66216 ██████████████████ | -- 65204 █████████████████▋ | -- 66228 ██████████████████ | hs/space-bslc8-chunk-3: n/a -- 1548 ▍ | -- 1644 ▌ | -- 75240 ████████████████████▍ | -- 66208 ██████████████████ | -- 75216 ████████████████████▍ | -- 66224 ██████████████████ | hs/space-bslc8-chunk-4: n/a -- 1512 ▍ | -- 1636 ▌ | -- 76188 ████████████████████▋ | -- 79232 █████████████████████▌ | -- 76176 ████████████████████▋ | -- 79204 █████████████████████▌ |

2 1

Class/Instance : what am I doing wrong in this example ?
by david48 21 Dec '07

21 Dec '07

I'm really inexperienced at this : ----------- {-# OPTIONS_GHC -fglasgow-exts -funbox-strict-fields -fallow-undecidable-instances -O2 #-} class Gadget g where fInit :: g -> a -> g data FString = FString !Int !String deriving Show instance Gadget FString where fInit (FString n _) s = FString n (take n s) ------------- I get the error message : Couldn't match expected type `String' against inferred type `a' `a' is a rigid type variable bound by the type signature for `fInit' at Gadget.hs:4:17 In the second argument of `FString', namely `s' In the expression: FString n s In the definition of `fInit': fInit (FString n _) s = FString n s

4 7

Creating a type for a subset of the integers
by Brad Larsen 21 Dec '07

21 Dec '07

Hi there list, How would one go about creating a new type for a subset of the integers, for (contrived) example just the even integers? I was thinking of making a new type newtype EvenInt = EvenInt Integer but the problem with this is that it accepts any integer, even odd ones. So to prevent this, the module does not export the constructor for it---rather, the module exports a function `mkEvenInt' that creates an EvenInt if the given value is acceptable or raises an error otherwise. What's the right way to do this? Thanks! Brad Larsen

5 6

Re: [Haskell-cafe] [HXT] Simple question
by Miguel Mitrofanov 20 Dec '07

20 Dec '07

> I can't really reproduce this: > A simple ghci session gives the following: > ----------------------------------- > uwe@si:~/haskell/hxt/curr/examples/arrows/HelloWorld> ghci HelloWorld.hs > GHCi, version 6.8.1: http://www.haskell.org/ghc/ :? for help > Loading package base ... linking ... done. > [1 of 1] Compiling Main ( HelloWorld.hs, interpreted ) > Ok, modules loaded: Main. > *Main> runX $ (readString [(a_validate,v_0)] "<x> </x>" >>> writeDocumentToString []) > Loading ... > ... > ["<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<x> </x>"] Try "<x><y> </y></x>" and a_indent writing option.

3 2

#haskell works
by Andrew Coppin 20 Dec '07

20 Dec '07

Many people have written words to the effect that the #haskell IRC channel is just bursting with helpful Haskellers who are endlessly friendly and seemingly able to help solve any problem. Personally, this has never been my experience. (More like there's 300 people idling and nobody ever actually speaks...) I am pleased to report that last night I was on #haskell and I did in fact get lots of useful help, from a number of people. So first of all, thanks for that guys! It all relates to this simple program: http://hpaste.org/4438 I pointed out that you can write a complex explicit loop in Java, and that you can translate the same thing into Haskell, and it works. But in Haskell, you can also do it by composing a couple of functions, and it's much easier to read. Somebody else countered that while this is all very cute, it can never be efficient. To which I obviously countered that stream fusion *makes* it efficient. The numbers generated are thus: Program with no particular optimisations: 0.35 seconds. Program with stream fusion [and GHC HEAD]: 0.25 seconds. Program with stream fusion and ByteString: 0.05 seconds. Surely you'd have to work pretty hard to get that kind of speed even in C. ;-) ...erm, actually no. Somebody sat down and wrote something in five minutes that takes 0.005 seconds. Oops! So it seems even with ByteStrings and stream fusion, we're still 10x slower than naive C. :-( You can console yourself that maybe 5 milliseconds is too short a time span to reliably measure, and maybe the speed difference is just down to the OS caching the file in RAM or something. Maybe a benchmark of something that takes tens of seconds would be better. All I know is that once again, it seems Haskell isn't as fast as I thought... *sigh* Well anyway, a few years ago we didn't have fusion, and we didn't have ByteString. A few years ago, the program would have taken 0.35 seconds. The end. Today, with a few import statements and compiler switches, the exact same code takes 0.05 seconds. Tomorrow, who knows? Maybe I'm being overly optimistic, but... ;-)

13 42

Storable types
by Clerton Filho 20 Dec '07

20 Dec '07

Hi, I'm newbie in Haskell, and I have some doubts... In this programming language, do we have storable values? Case affirmative, what are the storable types in Haskell, and how can I implement then... thanks! -- Clerton Ribeiro de Araujo Filho Graduando em Ciência da Computação Integrante do PET - Programa de Educação Tutorial Integrante do LIA - Laboratório de Inteligência Artificial Universidade Federal de Campina Grande - UFCG

4 3

Re: [Haskell-cafe] [HXT] Simple question
by Miguel Mitrofanov 20 Dec '07

20 Dec '07

Seems rather strange for me, I've just installed HXT and got this: Prelude Text.XML.HXT.Arrow> runX $ readString [(a_validate,"0")] "<this> </this>" >>> writeDocumentToString [] ["<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<this> </this>"] > Everything works fine except for the fact that all the nodes <this> > </this> > (that is, a space (an XML text node whose contents are a single space > character) > within a <this> element node) get transformed to a <this/> element node,

3 3

[HXT] Simple question
by Fernand 20 Dec '07

20 Dec '07

Hi, I'm using HXT (7.4) with GHC to make some XML transformations (BTW, congratulations to the maintainers of that package for their impressive work). Everything works fine except for the fact that all the nodes « <this> </this> » (that is, a space (an XML text node whose contents are a single space character) within a <this> element node) get transformed to a « <this/> » element node, which I do not want (I want to keep those nodes as they are). Note that my transformations do not change the <this> nodes or their children (my transformations works on others parts of the document). This seems to be related to the XML parsing or writing of the XML file, and I have tried several read/write options (using a_remove_whitespace and a_canonicalize with v_0, for both writing and reading) to prevent this behaviour, without success. I have even tried to add text childs nodes to all the empty <this> nodes, but the issue seems to lie in the XML output options. Has anybody an idea ? Excuse me if this is a trivial issue, Sincerely yours Fernand -- Excuse my french, it's my mother tongue.

2 1

Re: type trickery
by oleg＠okmij.org 20 Dec '07

20 Dec '07

Adrian Neumann wrote: > I figured I'd need something like this > data GF = GF Integer Integer > so that each element of the finite field would remember p. However I > can't think of a way to use the typesystem to ensure that p is always > the same. You might like: Vectro: Haskell library for "statically typed linear algebra" http://ofb.net/~frederik/stla/ which marks each element of a vector space with its dimension. The type system makes sure that you can only add vectors of the same dimension (the type system does even more: it computes the dimension of a result of multiplying a vector by a non-square matrix, for example). > I think that would need an infinite number of different types, You think correctly. Haskell already has the infinite number of different types (e.g., the infinite number of function types).

1 0

Class deriving in GHC 6.8
by Emil Axelsson 20 Dec '07

20 Dec '07

Hello all! How come in GHC 6.6 I could to write > {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances #-} > data Foo = Foo deriving Show > data Bar c = Bar (c Foo) deriving Show but in GHC 6.8.2 I get the error > No instance for (Show (c Foo)) > arising from the 'deriving' clause of a data type declaration > at Ert.hs:3:0-37 > Possible fix: add an instance declaration for (Show (c Foo)) > When deriving the instance for (Show (Bar c)) Thanks, / Emil

1 1

type trickery
by Adrian Neumann 20 Dec '07

20 Dec '07

Hello haskell-cafe! After making "data Number = Zero | Succ Number" an instance of Integral, I wondered how I could do the same with galois fields. So starting with Z mod p, I figured I'd need something like this data GF = GF Integer Integer so that each element of the finite field would remember p. However I can't think of a way to use the typesystem to ensure that p is always the same. I think that would need an infinite number of different types, but the type hackers here probably know something better. Adrian

2 1

Re: [xmonad] Re: XMonad.Layout.NoBorders
by gwern0＠gmail.com 20 Dec '07

20 Dec '07

On 2007.12.19 10:57:33 -0500, David Roundy <daveroundy(a)gmail.com> scribbled 0.3K characters: > No, I don't have time. And I'm not sure why one would want no borders > on floating windows... > > David Perhaps I don't fully understand the issues, but wouldn't such a thing be nice for things like MPlayer? The other day, I happened to play a video through MPlayer, and I noticed (using smartBorders/NoBorders) that there was an ugly border on the left and upper edges, and that it detracted from the cinematic experience. It was otherwise fullscreen and nice, but not as good as it could've been. -- gwern picking FID DES Mole Cap-Stun timers Z7 NAAP 2.6.2. ARC

1 0

Re: [Haskell-cafe] New to Haskell
by Miguel Mitrofanov 20 Dec '07

20 Dec '07

> >> As a user, I just want to be able to spot the basic components of a > >> source > >> file without thinking about transformation rules. > > Well, most users are. > Are what ? Sorry if I've confused you. English isn't my native language. "Are able", of course. > Have you asked them all ? If you're unsure, we can vote here or somewhere else. > >> Is this legal (`plus`) x y ? > > > > Never tried to write this myself, it looks stupid. > What else haven't you tried to write by know ? Well, I hope, I haven't tried to write the most of stupid-looking things. > > What kind of guarantees do you want? > Written in blood. Write it yourself, I don't have too much blood. > >> I just want the sistem to be able to print one of these expressions ! > >> Its this too much to ask ? > > Yes, 'cause it means you want to embed almost all source code into the > > compiled program. > So ? So, I don't know any compiler of any language which does it.

5 4

ANN: SearchPath v0.9
by Alex Jacobson 20 Dec '07

20 Dec '07

SearchPath v0.9 does recursive module chasing accross the internet using a combination of mapfiles you provide and the default map file, caching the downloaded modules in a local directory. Searchpath can handle modules in module hierarchies based at a URLs, in tgz archives accessible via URL, and in accessible darcs/svn/cvs etc repos at particular tags. New in v0.9 * handling tagged darcs/svn repos * handling .tgz archives * massive code cleanup * substantially faster * easier/better command line options * better usage documentation * handling non-local haskell files Check it out at http://searchpath.org. -Alex-

1 0

Is StateT what I need?
by Andre Nathan 20 Dec '07

20 Dec '07

Hello (Newbie question ahead :) I'm trying to write a program which will build a tree (here represented as a Map) of unix processes. The tree should be built by reading the process information stored in /proc/PID/status. There is also another Map which will be used for faster insertions on the process tree, which I'd like to handle as my program state. So far I have the functions to get a list of entries from /proc, filter the ones that represent processes and get the information from their status file. Now I need an "insertProc" function, which should get the information for a given process ID, update the state and return that information. This is where I think I need StateT, but I couldn't find out how to use it (never used StateT before...). This is what I have so far: > type Pid = FilePath > type Uid = String > > type PsData = Map String Uid > type PsChildren = Map Pid PsInfo > > data PsInfo = PsInfo PsData PsChildren > type PsMap = Map Pid PsInfo > type PsTree = Map Pid PsInfo > > parent :: PsData -> Pid > parent psData = fromJust $ Map.lookup "PPid" psData > > getProcInfo :: PsData -> String -> IO PsData > getProcInfo psData line = do > case matchRegex (mkRegex "^([a-z]+):[[:space:]]+(.*)$") line of > Nothing -> return (psData) > Just [key, value] -> return (Map.insert key value psData) > > procInfo :: Pid -> IO PsInfo > procInfo pid = do > procData <- readFile $ "/proc/" ++ pid ++ "/status" > psData <- foldM getProcInfo Map.empty (lines procData) > let [rUid, eUid, _] = words $ fromJust (Map.lookup "Uid" psData) > let [rGid, eGid, _] = words $ fromJust (Map.lookup "Gid" psData) > let uids = Map.fromList [("RUid", rUid), ("EUid", eUid), > ("RGid", rGid), ("EGid", eGid)] > let psData' = Map.union psData uids > return (PsInfo psData' Map.empty) I tried this for insertProc, but it obviously doesn't work... what would be the correct way to do this? > insertProc :: Pid -> StateT PsMap IO PsInfo > insertProc pid = do > proc <- procInfo pid -- XXX this is obviously wrong... > psMap <- get > put (Map.insert pid proc psMap) > return (proc) A second question: is it possible to make getProcInfo's type to be PsData -> String -> PsData and use some operation similar to lift so that it can be used with foldM, instead of making its return type to be IO PsData explicitely? Thanks in advance, Andre

11 17

Re: [Haskell-cafe] New to Haskell
by Miguel Mitrofanov 19 Dec '07

19 Dec '07

> What I should have been told about upfront: > - the syntax for an expression > - the syntax for a block Don't see your point. > - the adhoc syntax rules (how to distinguish among a tuple and a > pharanthesized expression and how to find the start and end of a block for > example ) Oh, that's pretty easy, parenthesized expression is not divided by a comma. > - what guarantees are made by the LANGUAGE that an IO action (such as do > putStrLn "Hello world" ) is not performed twice There are no such guarantees. If you write a = putStrLn "Hello world" main = do {a; a;} then your putStrLn would be performed twice. IO actions are first-class values, that's a feature, not a bug. > - the lambda expressions can be written (input) but cannot be printed > (output) Yes, since two different lambda expressions can denote the same function. > Here is some strange example: > module Hugs where > aa::Int > aa=7 > cc:: (Int->Int)->(Int->Int->Int)->Int->(Int->Int) > cc a op b = \x-> case x of { _ | x==aa -> x+1 ; _-> a x `op` b } > f::Int->Int > f(1)=1 > f(2)=2 > f(_)=3 > g::Int->Int > g(1)=13 > g(2)=23 > g(_)=33 > h::[Int->Int] -> Int ->Int > h [] x = x > h [rr] x = let { u=Hugs.f ; v=Hugs.g } in case rr of { u -> > Hugs.g(x)+aa ; v -> Hugs.f(x)+aa ; _ ->rr (x) + aa } > h (rr:ll) x = h [rr] x + h (ll) x > What I don't understand is why I'm forced to use guards like x==aa in cc, > when aa is clearly bounded (is 7) and why in function h, the bounded u and > v become free variables in the case expression. No, pattern matching bounds variables; if you write "case x of {aa -> ...} then aa becomes a LOCAL variable for the case statement, and shadows the global definition. The same applies to u and v in h, except that in this case local variables shadow upper-level local variables.

7 18

New to Haskell: The End
by Cristian Baboi 19 Dec '07

19 Dec '07

Haskell strengts as I see them: - it is "lazy with class" - it is strongly typed - it has automatic memory management - it has a standard library - it has a compiler - it is available on several platforms - it has a community - it is free Is there anything you would like to add ? ________ Information from NOD32 ________ This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com

9 9

Haskell purity and printing
by Cristian Baboi 19 Dec '07

19 Dec '07

This is what I "understand" so far ... Suppose we have these two values: a) \x->x + x b) \x->2 * x Because these to values are equal, all functions definable in Haskell must preserve this. This is why I am not allowed to define a function like h :: (a->b) -> (a->b) h x = x The reasons are very complicated, but it goes something like this: - when one put \x->x+x trough the function h, the compiler might change it to \x -> 2*x - when one put \x->2*x trough the function h, the compiler might change it to \x -> x + x And we all know that \x -> 2*x is not the same as \x->x+x and this is the reason one cannot define h in Haskell

5 6

[ANN] Wadler talk in San Francisco on Jan 9, 2008
by Keith Fahlgren 19 Dec '07

19 Dec '07

Hi all, Philip Wadler will be in San Francisco for POPL '08 so the Bay Area Functional Programmers have asked him to reprise his ICFP '07 talk "Well-typed programs can’t be blamed". He's been good enough to set us up with a proper room in the ACM conference hotel. The meeting will take place in the Stanford Room, The Stanford Court Hotel, San Francisco at 7:30pm on Wednesday, January 9th, 2008. Please watch http://groups.google.com/group/bayfp or http://www.bayfp.org/blog/ for more details and pass this along to others in the area that might be interested. Thanks, Keith

1 0

A Show instance for simple functions
by Benja Fallenstein 19 Dec '07

19 Dec '07

Hi all, Below is a program that implements Show for functions whose type is composed of only (->) and type variables (or, more precisely, of (->) and (State Int Term), but any type composed of (->) and type variables can obviously be specialized to that). (-fglasgow-exts is needed only for the convenience of being able to declare "instance MkTerm (State Int Term)" -- if we'd wrap the State Int Term in a newtype, as far as I can see this would be H98.) - Benja {-# OPTIONS_GHC -fglasgow-exts #-} import Control.Monad import Control.Monad.State import Data.Char data Term = Var Int | App Term Term | Lam Int Term showVar i = [chr (ord 'a' + i)] showTerm :: Term -> String showTerm (Var i) = showVar i showTerm (Lam i x) = "\\" ++ showVar i ++ " -> " ++ showTerm x showTerm (App f x) = showTerm f ++ " " ++ showArg x where showArg (Var i) = showVar i; showArg x = "(" ++ showTerm x ++ ")" class MkTerm a where argument :: State Int Term -> a mkTerm :: a -> State Int Term instance MkTerm (State Int Term) where argument = id mkTerm = id instance (MkTerm a, MkTerm b) => MkTerm (a -> b) where argument f x = argument $ liftM2 App f (mkTerm x) mkTerm f = do i <- get; modify (+1) body <- mkTerm (f (argument (return (Var i)))) return $ Lam i body instance (MkTerm a, MkTerm b) => Show (a -> b) where show f = showTerm $ evalState (mkTerm f) 0 type X = State Int Term main = do print (id :: X -> X) print (id :: (X -> X) -> (X -> X)) print ((.) :: (X -> X) -> (X -> X) -> (X -> X)) print ((\x y -> y x) :: X -> (X -> X) -> X) print ((\f x -> f x x) :: (X -> X -> X) -> X -> X) print ((\f -> f id id) :: ((X -> X) -> (X -> X) -> X) -> X)

1 0

OOP'er with (hopefully) trivial questions.....
by Nicholls, Mark 19 Dec '07

19 Dec '07

I'm trying to teach myself Haskell....I've spent a few hours going through a few tutorials....and I sort of get the basics... My interest in Haskell is specifically around the strength of the type system. After many years of OOP though my brain is wired up to construct software in that 'pattern'....a problem for me at the moment is I cannot see how to construct programs in an OO style in Haskell....I know this is probably not the way to approach it...but I feel I need to master the syntax before the paradigm. I'm not fussed about mutability, and I'm not fussed about implementation inheritance (as apposed to subtyping).... my concerns are encapsulation of 'state' and abstraction, and extension/expansion....a simple example would be. interface IShape { Int GetArea(); } class Square : IShape { Readonly int length; Public Square(int length) { this.length = length; } Int GetArea() { return length * length;} } Class Rectangle : IShape { Readonly int lengthA; Readonly int lengthB; Public Rectangle (int lengthA,int lengthB) { this.lengthA = lengthA; this.lengthB = lengthB; } Int GetArea() { return lengthA * lengthB;} } Class Circle : IShape { Readonly int radius; Public Circle(int radius) { this.radius = radius; } Int GetArea() { return pi * radius * radius;} } Client code..... Void Foo(IShape shape) { // look!....I know nothing except its of type IShape. Int area = shape.GetArea(); } I can obviously at a later date add a new class Triangle, and not have to touch any of the above code....

28 52

Foldable Rose Trees
by Dominic Steinitz 19 Dec '07

19 Dec '07

I've been trying to re-label nodes in a rose tree without re-inventing wheels (although I'm beginning to wish I had). I've got as far as this but haven't yet cracked the general case for Traversable. Any help would be much appreciated. Thanks, Dominic. > *Main> let (p,_) = runState (unwrapMonad (traverse (\x -> WrapMonad update) (Rose' 3 [Rose' 5 [Rose' 11 [Rose' 19 []], Rose' 13 [], Rose' 17[]], Rose' 7 []]))) 0 in p > Rose' 0 [Rose' 1 [Rose' 2 [Rose' 3 []],Rose' 4 [],Rose' 5 []],Rose' 6 []] > import Control.Applicative > import Data.Foldable > import Data.Traversable > import Data.Monoid > import Control.Monad.State > > update :: MonadState Int m => m Int > update = > do x <- get > put (x + 1) > return x > > data Rose' a = Rose' a [Rose' a] > deriving Show > > instance Functor Rose' where > fmap f (Rose' x rs) = Rose' (f x) (map (fmap f) rs) > > instance Foldable Rose' where > foldMap f (Rose' x rs) = f x `mappend` (mconcat (map (foldMap f) rs)) > > instance Traversable Rose' where > traverse f (Rose' x []) = Rose' <$> f x <*> pure [] > traverse f (Rose' x [x0]) = Rose' <$> f x <*> (pure (\x -> [x]) <*> traverse f x0) > traverse f (Rose' x [x0,x1]) = Rose' <$> f x <*> (pure (\x y -> x:y:[]) <*> traverse f x0 <*> traverse f x1) > traverse f (Rose' x [x0,x1,x2]) = Rose' <$> f x <*> (pure (\x y z -> x:y:z:[]) <*> traverse f x0 <*> traverse f x1 <*> traverse f x2)

2 2

list utilities -- shouldn't these be in the hierarchical libs somewhere?
by Thomas Hartman 19 Dec '07

19 Dec '07

I found http://haskell.cs.yale.edu/haskell-report/List.html had many useful "one off" type list functions such as "subsequences" and "permutations" which are nowhere to be found in hoogle, Data.List, or the haskell hierarchical libs Shouldn't these be included somewhere? thomas. --- 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.

3 2

New to Haskell
by Cristian Baboi 18 Dec '07

18 Dec '07

A few days ago, for various reasons, I've started to look at Haskell. At first I was quite impressed, after reading some FAQ, and some tutorials. Evrything was nice and easy ... until I've started writing some code on my own. What I should have been told about upfront: - the syntax for an expression - the syntax for a block - the adhoc syntax rules (how to distinguish among a tuple and a pharanthesized expression and how to find the start and end of a block for example ) - the fact that lambda expressions are not the same thing as "algebraic data" values - what guarantees are made by the LANGUAGE that an IO action (such as do putStrLn "Hello world" ) is not performed twice - the lambda expressions can be written (input) but cannot be printed (output) The biggest problem for me, so far, is the last one. Here is some strange example: module Hugs where aa::Int aa=7 cc:: (Int->Int)->(Int->Int->Int)->Int->(Int->Int) cc a op b = \x-> case x of { _ | x==aa -> x+1 ; _-> a x `op` b } f::Int->Int f(1)=1 f(2)=2 f(_)=3 g::Int->Int g(1)=13 g(2)=23 g(_)=33 h::[Int->Int] -> Int ->Int h [] x = x h [rr] x = let { u=Hugs.f ; v=Hugs.g } in case rr of { u -> Hugs.g(x)+aa ; v -> Hugs.f(x)+aa ; _ ->rr (x) + aa } h (rr:ll) x = h [rr] x + h (ll) x What I don't understand is why I'm forced to use guards like x==aa in cc, when aa is clearly bounded (is 7) and why in function h, the bounded u and v become free variables in the case expression. ________ Information from NOD32 ________ This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com

5 7

Multiple statements with Where
by insertjokehere 18 Dec '07

18 Dec '07

Hi all, I am having problems adding multiple definitions with where for example in my code --A parser for recognising binary operations parseBinaryOp :: String -> String -> [(Expr, Expr, String)] parseBinaryOp op str | (elem op binops) && (notElem '(' (snd bm)) && (notElem ')' (snd bm)) && (elem nstr!!1 binops) = [(EInt 1, EInt 1, "HERE!")] | otherwise = [] where bm = bracketMatch str nstr = words (snd (bracketMatch str)) I get the error message parse error on input `=' Essentially this function is supposed to parse binary operations in a string, nstr is just a [String], binops is a list of Strings. The types appear to be fine, and GHCI dosnt say that this is the problem, the problem seems to lie with that definition of nstr after the definition of bm. I believe I have followed the definitions correctly, so I am at a loss for how to solve this problem. The list that is given for the first case is only a placeholder, once I get past this problem I should be able to make the function operate properly Any help would be much appreciated, please tell me if you need more info. Thankyou :-) -- View this message in context: http://www.nabble.com/Multiple-statements-with-Where-tp14397482p14397482.ht… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 3

Re: [Haskell-cafe] Re: New to Haskell
by Miguel Mitrofanov 18 Dec '07

18 Dec '07

> > Yes, and Haskell can do it also. But C, I guess, can't print out a > > source code for a function (well, there can be some weird dialects of C > > I'm not aware about). Haskell can't do it either. > Well, LISP can, if I remember it right. Only in an interpreter, if I remember it right.

2 1

Re: [Haskell-cafe] Re: New to Haskell
by Miguel Mitrofanov 18 Dec '07

18 Dec '07

> >> - the lambda expressions can be written (input) but cannot > >> be printed (output) > > This is a fundamental property of the language. A lambda > > expression is programme and at runtime the system doesn't > > know one lambda expression from another (all it can do with > > one is apply it to something). > Even C can apply a function variable to an argument (function pointers). Yes, and Haskell can do it also. But C, I guess, can't print out a source code for a function (well, there can be some weird dialects of C I'm not aware about). Haskell can't do it either.

2 1

Re: [Haskell-cafe] New to Haskell
by Miguel Mitrofanov 18 Dec '07

18 Dec '07

> >> - the syntax for an expression > >> - the syntax for a block > > Don't see your point. > The point is the syntax is introduced as transformation of layout form to > non layout form. > As a user, I just want to be able to spot the basic components of a source > file without thinking about transformation rules. Well, most users are. > > Oh, that's pretty easy, parenthesized expression is not divided by a > > comma. > Thanks! What is the end of a block ? What introduce new blocks ? Not sure what you mean by "block" here. > Is this legal (`plus`) x y ? Never tried to write this myself, it looks stupid. > It's this a tuple ? ([a,b,c,d ]) ? No, since all commas are in the subexpression. > > then your putStrLn would be performed twice. IO actions are first-class > > values, that's a feature, not a bug. > What guarantees that by running the main, the string "Hello world" will be > printed exactly twice ? What kind of guarantees do you want? > I just want the sistem to be able to print one of these expressions ! > Its this too much to ask ? Yes, 'cause it means you want to embed almost all source code into the compiled program.

2 1

Re: [Haskell-cafe] OOP'er with (hopefully) trivial questions.....
by Miguel Mitrofanov 18 Dec '07

18 Dec '07

> class Shape a where { > intersect :: Shape b => a -> b -> Bool > } > data Shape a = { intersect :: Shape b => a -> b -> Bool } > in fact, the syntax is rather similar, too! :) Um, well, and how are you going to implement it?

2 1

Compiling GLFW / SOE on Windows
by Peter Verswyvelen 18 Dec '07

18 Dec '07

Hi, This might be a tip for people trying to compile the GLFW package bundled with SOE on Windows. I had to because I slightly modified the GLFW source code. The SOE readme.txt says: "For Win32 users, you'll need MinGW environment to compile GLFW. If "make win32-mgw" is unable to execute compile.bat propperly, use "compile.bat mgw". Please also make sure that your MinGW path should come before the GHC's gcc-lib path in the PATH environment." However, the readme.html file has the following note: Do not use the MSYS shell for compiling GLFW, because the supplied batch file "compile.bat" will only work under a Windows command prompt (or MS-DOS prompt). To get it working, I basically needed to modify my PATH environment variable so that it contains the MSYS bin folder (in my case C:\app\msys\1.0\bin), and then run "COMPILE.bat make mgw" file using the Windows command prompt (CMD.EXE) instead of the MSYS unix shell emulator... Cheers, Peter

1 1

Questions about the Functor class and it's use in "Data types à la carte"
by Corey O'Connor 18 Dec '07

18 Dec '07

I'm working through the interesting paper "Data type à la carte" and am confused by the Functor instance for Val. I think this stems from some confusion of mine regarding the Functor class in general. The Functor instance I'm confused about is: instance Functor Val where fmap f (Val x ) = Val x where Val is defined as: data Val e = Val Int Is this the only valid Functor instance for the Val type? Even though I'd, naively, expect the Functor instance to look like: instance Functor Val where fmap f (Val x) = Val (f x) I suspect that would not work out due to the type of the Val constructor. Is this correct? The reason I find all this odd is because I'm not sure how the type class Functor relates to the category theory concept of a functor. How does declaring a type constructor to be an instance of the Functor class relate to a functor? Is the type constructor considered a functor? Any help would be, of course, greatly appreciated. -Corey O'Connor

14 26

gtk2hs treeview problem (Windows)
by Jian Fan 18 Dec '07

18 Dec '07

I installed ghc 6.6.1 and 0.9.12.1. I'm trying to use the tree view widget. To enable search in treeview, I added following 2 lines: New.treeViewAppendColumn view col3 -- my addition New.treeViewSetEnableSearch view True New.treeViewSetSearchColumn view 0 in demo/treeList/TreeDemo.hs The program crashes if I press any key. The console shows: C:\Gtk2Hs\demos\treeList>TreeDemo.exe (TreeDemo.exe:3064): GLib-GObject-WARNING **: gtype.c:3339: type id `0' is inval id (TreeDemo.exe:3064): GLib-GObject-WARNING **: can't peek value table for type `< invalid>' which is not currently referenced I also tried ghc 6.8.1 with the same result. Any hints? Thanks. Jian

1 0

class default method proposal
by Duncan Coutts 18 Dec '07

18 Dec '07

I'd just like to float an idea that's related to the Class Alias proposal[1] but is perhaps somewhat simpler. We all know that Functor should have been a superclass of Monad, and indeed we now know that Applicative should be too. Making such a change would break lots of things however so the change does not happen. However in this case the Monad operations can be used to implement the Functor and Applicative class methods. So it would be nice if we could get them for free if the author did not choose to write the Functor and Applicative instances. So my suggestion is that we let classes declare default implementations of methods from super-classes. class Functor m => Monad m where {- the ordinary bits -} fmap f m = m >>= return . f So if there already is a Functor instance for m then the default implementation of fmap is not used. Does this proposal have any unintended consequences? I'm not sure. Please discuss :-) Duncan [1] http://repetae.net/recent/out/classalias.html

17 25

Yampa / AFRPVectorSpace.hs
by Peter Verswyvelen 18 Dec '07

18 Dec '07

While studying the vector space class in AFRP, I encountered the following strange code: class Floating a => VectorSpace v a | v -> a where ... v1 ^-^ v2 = v1 ^+^ v1 -- (negateVector v2) I have no idea why the (negateVector v2) has been commented out, but surely this must be a typo? Cheers, Peter

5 5

Problem with a Win32 API
by Eric 17 Dec '07

17 Dec '07

Dear all, When I run the program below a window appears for a split second, then disappears and the program exits. Can you help me figure out what's going wrong? *** import Graphics.Win32.Misc import Graphics.Win32.GDI.Types import Graphics.Win32.Window import System.Win32.DLL import Foreign.Marshal.Alloc main = do hInst <- loadLibrary "ole32.dll" res <- registerClass (style, hInst, Nothing, Nothing, Nothing, Nothing, classname) if res == Nothing then do{putStrLn "Unable to register." ;return()} else putStrLn "Registered." hwnd <- createWindow classname "Kleer 0" wS_VISIBLE Nothing Nothing Nothing Nothing Nothing Nothing hInst handler b <- showWindow hwnd sW_SHOWNORMAL if b then putStrLn "Window showing" else do{putStrLn "Unable to show window."; return()} updateWindow hwnd ptr <- mallocBytes 4 getMessage ptr Nothing loop ptr loop msg = do translateMessage msg dispatchMessage msg loop msg handler :: WindowClosure handler hwnd msg w l = case msg of wM_CLOSE -> do{destroyWindow hwnd; return 0} _ -> defWindowProc (Just hwnd) msg w l style :: ClassStyle style = 0 classname = mkClassName "KleerWnd" *** E.

1 0

array documentation is missing
by Thomas Hartman 17 Dec '07

17 Dec '07

While trying to make Regex.TDFA 0.91 install on 6.8.2 I got [10 of 21] Compiling Text.Regex.TDFA.RunMutState ( Text/Regex/TDFA/RunMutState.\ hs, dist\build/Text/Regex/TDFA/RunMutState.o ) Text/Regex/TDFA/RunMutState.hs:601:9: Constructor `STUArray' should have 4 arguments, but has been given 3 In the pattern: STUArray _ _ msource In the definition of `copySTU': copySTU (STUArray _ _ msource) (STUArray _ _ mdest) = ST $ \ s1# -> case sizeofMutableByteArray# msource of n# ->\ ... ^[]0;~/hackageTarGzs/regexstuff/regex-tdfa-0.92^G ^[[32mhartthoma@dbnycws28816 ^[[33m~/hackageTarGzs/regexstuff/regex-tdfa-0.92^[\ [0m but I got stuck fixing it because the array documentation isn't there http://www.haskell.org/ghc/docs/latest/html/libraries/haskell98/Array.html assume I'm getting the above error because the array interface has changed thomas. --- 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.

3 2

Patter matching beginner question
by Adam Smyczek 17 Dec '07

17 Dec '07

Hi all, I assume the following behavior has a trivial explanation. When I write: case name of "a" -> ... "b" -> ... everything works fine. But when I extract a and b to constants: c_a = "a" :: String c_b = "b" :: String case name of c_a -> ... c_b -> ... I get Patterns match(es) are overlapped. Adam

3 2

Implementing a MUD server in haskell
by Jack Kelly 17 Dec '07

17 Dec '07

Hi, I've been thinking about two things for some time now: 1. Sharpening my haskell 2. Implementing a MUD server I've been thinking about doing (1) and (2) at the same time but I've run into some problems with data structures. I need to be able to get a list of players from a room (for things like a 'look' command) and I need to be able to find which room contains a given player. I'm still looking at this problem through an imperative lens, so here's some sort-of-C: struct room{ ... struct player * players; ... }; struct player{ ... struct room * room; ... }; From what I can see, I'd use a record type for players and rooms, but I'm not sure how to replicate the pointer effects: keeping each player pointing to a single instance of a consistent world and maintaining the invariant that (given: p :: Player, r :: Room): p `elem` (Room.players r) => (Player.room p == r) This needs to stand up to concurrent modification of a shared world structure, but I think I'll set up the concurrency controls after I get my head around this. -- Jack

4 4

Re[2]: [Haskell-cafe] Execution of external command
by Bulat Ziganshin 16 Dec '07

16 Dec '07

Hello gwern0, Thursday, December 13, 2007, 4:43:02 PM, you wrote: > to get at stdout. I don't think this would go through cmd/sh, but > honestly, specifying a particular interpreter breaks your > portability anyway these scripts will be written by users so they don't need to be the same for win&unix. i guess that users will prefer to use perl or something like this for these scripts and afaiu in both windows and linux this need to go through sh/cmd it seems that script may be not terminated if its output isn't read, so better code should be (_, h, g, _) <- runInteractiveCommand "script params" result <- hGetLine h hGetContents h >>= evaluate.length hGetContents g >>= evaluate.length am i right? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

6 6

Cheap ByteString mmap
by Don Stewart 16 Dec '07

16 Dec '07

A little mmap binding for ByteStrings. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring-mmap-… Should be useful for managing file resources under pressure (cheaper than a readFile, and with different constraints). Posix only. the Win32 mmap for bytestrings is in the win32 package. -- Don

1 0

JOB OFFER / Haskell for commercial projects?
by Peter Verswyvelen 16 Dec '07

16 Dec '07

Hello Happy Haskellers, I had to abandon improving my newbie Haskell skills the past weeks; I was busy creating a new startup company and finalizing financial funding for a cool project related to realtime "2D/3D animation and games". As I'm the CTO of this new company, and since I kinda like Haskell, I might consider creating a first prototype of the project using Haskell. However, this will be a commercial project. The software will be freely downloadable but not open source. However, if succesful, a highly priced professional version of the software might be created. Although I'm pretty sure GHC can be used for creating a private inhouse prototype, the prototype might evolve into the final product, and so my question is, which Haskell compilers & tools can: (1) be used to build commercial projects (2) be shipped with commercial projects (our project might call into the interpreter/compiler at runtime.) (3) be indirectly used by commercial projects (in the sense that the user will have to manually download and install the compiler) Furthermore, is the Haskell community willing to provide the excellent help (as in this forum and on IIRC) for commercial Haskell projects? That said, anybody who might be interested in getting a (paid J) Haskell job (parttime or fulltime) in the field of computer animation and games (but also (visual) programming languages, interpreters & compilers), please mailto:peter@nazooka.com. Preferable you will work onsite (in Belgium / Antwerp - the city of diamonds J), although working remote is also an option. You will make software that will be initially used by computer artists (that among other things made parts of <http://www.cgchannel.com/gallery/viewimage.jsp?imgID=547> "The Girl", Xyanide <http://www.gamespot.com/xbox/action/xyanide/index.html> , and many commercials <http://www.nazooka.com/site/html/index.php?p=movieplayer&m=showreel> ), that will be demonstrated at SIGGRAPH <http://www.siggraph.org/> , and will be released to the public in a later stage. Cheers to all, Peter Verswyvelen

7 6

getMessage function in Win32 API
by Eric 16 Dec '07

16 Dec '07

Dear all, In the Graphics.Win32.Window package there is a function getMessage takes a value of type LPMSG. How can I construct a value of LPMSG so that I can call the function? E.

1 0

A Random Question
by Dominic Steinitz 16 Dec '07

16 Dec '07

I need to generate distinct arbitrary values for my quickcheck tests and they don't have to be arbitrary (although that doesn't matter). No problem I thought, I'll create my own random number generator (which will not be random at all) and use > choose :: forall a. (Random a) => (a, a) -> Gen a Here's my code: > import Test.QuickCheck > import System.Random > > data MyGen = MyGen Int > deriving (Eq, Show) > > myNext :: MyGen -> (Int, MyGen) > myNext (MyGen s1) = > (s1, MyGen (s1 + 1)) > > -- Assume we will never need this > mySplit :: MyGen -> (MyGen, MyGen) > mySplit = error "No split for predictable random generator" > > myGenRange :: MyGen -> (Int, Int) > myGenRange (MyGen s1) = (s1, s1) > > instance RandomGen MyGen where > next = myNext > split = mySplit > genRange = myGenRange > > data Foo = Foo Int > deriving (Eq, Show) > > myRandomR :: (Foo, Foo) -> MyGen -> (Foo, MyGen) > myRandomR (Foo lo, Foo hi) g = > let (n, g') = next g > in (Foo n, g') > > instance Random Foo where > randomR = myRandomR > random = undefined But I get > Supply.hs:33:13: > Couldn't match expected type `g' against inferred type `MyGen' > `g' is a rigid type variable bound by > the type signature for `randomR' at <no location info> > Expected type: (Foo, Foo) -> g -> (Foo, g) > Inferred type: (Foo, Foo) -> MyGen -> (Foo, MyGen) > In the expression: myRandomR > In the definition of `randomR': randomR = myRandomR > Failed, modules loaded: none. I have two questions: 1. Why can't I instantiate a type class with any function I like provided it fits the type signature? 2. Is this the right approach to generating predictable arbitrary values? Are there others? Thanks, Dominic.

5 7

Fw: hdbc odbc also crashes on 6.8.2 Re: [Haskell-cafe] HDBC-ODBC crashes on ghc 6.8
by Thomas Hartman 16 Dec '07

16 Dec '07

I just tried HDBC-ODBC on 6.8.2, but it still crashes. Works on 6.6.1. thomas. Thomas Hartman <thomas.hartman%2Bexternal(a)db.com> Sent by: haskell-cafe-bounces(a)haskell.org 11/19/2007 12:05 PM To haskell-cafe(a)haskell.org cc Subject [Haskell-cafe] HDBC-ODBC crashes on ghc 6.8 This minimal program below fails in 6.8.1, works for 6.6.1, for up to date HDBC-ODBC-1.1.3. (I tried installing both from package and from darcs head) Installed and running from cygwin. When I run it as runghc fail.hs I get a windows popup error "ghc.exe has encountered a problem and needs to close, sorry for the inconvenience". ghci, same behavior. When I run it as ghc -e 'main' fail.hs, I don't get a popup window, and no error message is output, but it fails all the same. (I know this because more complicated, non-minimal programs, fail.) So this would seem to be a problem with ghc 6.8.1. $ cat fail.hs import Database.HDBC import Database.HDBC.ODBC main = connectODBC "some valid connect string, works when run from 6.6.1, not from 6.8.1" --- 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. _______________________________________________ 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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New slogan for haskell.org
by gwern0＠gmail.com 15 Dec '07

15 Dec '07

FWIW to the discussion about changing the main page, I was reading the CUFP paper and I saw some germane comments (and the writer is apparently one Noel Welsh, whose name I don't see in the thread); the context is a discussion (pg 17) of various members or potential members of the Haskell community and how supported they are: "What are the needs of the potential programmer? People program to solve prob- lems; so there had better be a clear statement of what kinds of problem the language is good for. The Python community does a good job of this on python.org: "Python is a dynamic object-oriented programming language that can be used for many kinds of software development. It offers strong support for integration with other languages and tools, comes with extensive standard libraries, and can be learned in a few days." Compare this with the equivalent from haskell.org: "Haskell is a general purpose, purely functional programming language featuring static typing, higher-order functions, polymorphism, type classes, and monadic effects. Haskell compilers are freely available for almost any computer." If you understand all that, you don't need to be here: you're already a Haskell programmer." -- gwern

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