August 2011 - Haskell-Cafe

only anecdotal .... not a proof of a trend ...
by Vasili I. Galchin 29 Aug '11

29 Aug '11

Hello, I received two job postings ... my comments follows the postings: ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- *#1 Software Developer* * * Location: Austin, TX Duration: 6 months Rate : $60/hr -$70/hr on w2 *Required:* *- Straight C experience - Generally need a pure C programmer to ideally create 1 C file that can be compiled in Win32/Win64/Dos/Shell/Linux* a. Prefer C, not C++, but if only C++ still consider it. b. Past contractors tried to do too large of things like templates, huge class structures, etc. so we prefer C over C++ c. Upper level Windows programming such as .NET detracts because client wants them to think about all targets, not just Windows *- Linux experience – Generally need to get a Windows GUI application to be re-compiled and run in Linux* a. Hard to find, so first do a key word search of Linux b. Programming applications background is a big plus c. Looking for GUI experience so they can scope how the Win32 app looks then implement the same experience in Linux d. Client is lacking in Linux background, so need someone that needs minimal help with Linux. *Desired:* - Application development – Have several Win32 applications that need to be compiled as Win64 then tested a. Experience in testing and familiar with looking for corner case scenarios - Low level hardware/software interaction knowledge a. Apps require running a SMI to initiate contact, need candidate to understand difference between virtual and flat addressing ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- *#2 SMTP EMAIL SERVER - C* Elance - United States See original job posting at Elance »<http://www.indeed.com/rc/clk?jk=6f0fdd27079eb247&from=vj&grandfrom=ja&tk=16…> Developer to provide ANSI C software to send (receive not required) email using an SMTP Server. This software must support: ? AUTH_LOGIN (base 64 encoding) ? NTLM ? NTLM2 ? CRAM MD5 This software is targeted to run on an embedded microcontroller but can be developed in Linux or Windows. The following requirements MUST be met: ? No C++, No C++ Classes...etc ? No .NET ? No DLLs ? No Libraries ? No OS dependencies (Windows/QNX/MQX or any other OS) ? No OS Function Calls ? 100% ANSI C Source is required. Desired Skills: C ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Both seem to want to have nothing with C++ (dare I say OOPS?). I work in mainstream industry. Have others on the mail list seen such job postings recently? Is there now a trend against C++ due to somewhat loose type checking and very statefullness? (Unlike Haskell which splits pure and monads very clearly vis strong types). #1 To C++ templates are much more bulky(and ugly) compared Haskell's polymorphic types. However, it caused me to think where we Haskell programmers can do "too large of things". ??? Perhaps an unfair question given that I have no access to the current C++ code. #2 >From the context of #2, I can tell the author didn't mean all of the "?"'s but instead maybe "!". The OS QNX is a hard real-time OS that uses a message passing IPC. I have worked QNX and have written a device driver for QNX. This job posting maybe very unfair argument against C++/OOPs as maybe the thought is that C++ adds to much "non-determinism" to a hard real-time problem. In the real-time extension to the POSIX API is a function "mlock" which locks a process into memory(no swapping) which seriously helps to cut down on non-determinism. Here Haskell would be worse with its garbage collector with its attending non-determinism. No "OS function calls" seems way over the top. Sorry for my meandering thinking .... Regards, Vasili

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Re: [Haskell-cafe] Project Euler: request for comments
by KC 28 Aug '11

28 Aug '11

Try something like the following: -- Project Euler 11 -- In the 20×20 grid below, four numbers along a diagonal line have been marked in red. -- <snip> -- The product of these numbers is 26 × 63 × 78 × 14 = 1788696. -- What is the greatest product of four adjacent numbers in any direction (up, down, left, right, or diagonally) in the 20×20 grid? import Data.List -- Doing the one dimensional case. f011 :: [Int] -> Int f011 (t:u:v:xs) = f011helper t u v xs f011helper :: Int -> Int -> Int -> [Int] -> Int f011helper t u v (w:ws) | ws == [] = t*u*v*w | otherwise = yada nada mada -- What are yada nada mada? -- The 20x20 grid case will become: f0112D :: [[Int]] -> Int -- where [[Int]] is a list of lists of rows, columns, major diagonals, & minor diagonals. On Sun, Aug 28, 2011 at 5:10 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > No. The answer I posted is not good. > It worked, by chance, on a couple of small examples I tried but it > could end up comparing sequence of 4 numbers that where not initially > adjacent. > > On Sun, Aug 28, 2011 at 12:32 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: >> Maybe this? >> >> f x@(a:b:c:d:[]) = x >> f (a:b:c:d:e:ys) = if e >= a >> then f (b:c:d:e:ys) >> else f (a:b:c:d:ys) >> >> On Sat, Aug 27, 2011 at 8:26 PM, KC <kc1956(a)gmail.com> wrote: >>> Think of the simplest version of the problem that isn't totally trivial. >>> >>> e.g. A one dimensional list of numbers. >>> >>> What would you do? >>> >>> Note: you only want to touch each element once. >>> >>> The 2 dimensional case could be handled by putting into lists: rows, >>> columns, major diagonals, and minor diagonals. >>> >>> This isn't the fastest way of doing the problem but it has the >>> advantage of avoiding "indexitis". >>> >>> -- -- Regards, KC

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Re: [Haskell-cafe] Make shared library - questions
by David Banas 28 Aug '11

28 Aug '11

> I'm trying to compile shared library. This library will use as part of > plugin for some program. > If I compile library with option -dynamic my library has links for HS > libraries like libHSbase-4.2.0.2-ghc6.12.3.so and so on. > But program has crashed constantly. > > Is it possible to make shared library without -dynamic flag? I want to > try > to make library without dependencies. I struggled with this, too. Here's my makefile, which is now working: 1 GCC = gcc 2 CFLAGS += -I/usr/lib/ghc-6.12.3/include/ -g -fPIC 3 4 HC = ghc 5 HC_OPTS = -cpp $(EXTRA_HC_OPTS) 6 EXTRA_HC_OPTS = -package parsec 7 HC_LOPTS = -no-hs-main -shared -package parsec 8 #GHCOPTS := -prof -auto-all -caf-all 9 10 HSRCS = AMIParse.hs AMIModel.hs ApplicativeParsec.hs 11 CSRCS = ami_model.c ami_test.c 12 SRCS = $(HSRCS) $(CSRCS) 13 OBJS = AMIParse.o AMIModel.o ami_model.o AMIModel_stub.o ApplicativeParsec.o 14 15 .SUFFIXES : .o .hs .hi .lhs .hc .s .c 16 .PHONY : all depend rebuild clean 17 18 all: ami_test 19 20 ami_test: ami_test.o libami.so 21 $(HC) -dynamic -o $@ -L. -lami ami_test.o 22 23 libami.so : $(OBJS) 24 rm -f $@ 25 $(HC) -o $@ $(HC_LOPTS) $^ 26 27 depend: 28 $(HC) -M $(HC_OPTS) $(HSRCS) 29 30 rebuild: 31 $(MAKE) clean 32 $(MAKE) all 33 34 clean: 35 rm -f *.hi *.o *.out ami_test *.so 36 37 # Standard suffix rules 38 .o.hi: 39 @: 40 41 .lhs.o: 42 $(HC) -c $< $(HC_OPTS) 43 44 .hs.o: 45 $(HC) -c $< $(HC_OPTS) 46 47 .o-boot.hi-boot: 48 @: 49 50 .lhs-boot.o-boot: 51 $(HC) -c $< $(HC_OPTS) 52 53 .hs-boot.o-boot: 54 $(HC) -c $< $(HC_OPTS) 55 56 # Individual cases 57 AMIModel_stub.o: AMIModel.hs 58 $(HC) -c $< $(HC_OPTS) 59 60 # DO NOT DELETE: Beginning of Haskell dependencies 61 ApplicativeParsec.o : ApplicativeParsec.hs 62 AMIParse.o : AMIParse.hs 63 AMIParse.o : ApplicativeParsec.hi 64 AMIModel.o : AMIModel.hs 65 AMIModel.o : AMIParse.hi 66 # DO NOT DELETE: End of Haskell dependencies Good luck! -db

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haskell-src-exts should depend on happy
by Ozgur Akgun 28 Aug '11

28 Aug '11

Hi, cabal installing haskell-src-exts fails, because of an unlisted dependency to the happy executable. The following succeeds: cabal install happy; cabal install haskell-src-exts Thanks, Ozgur

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Class instances in haddock documentation missing
by Joachim Breitner 28 Aug '11

28 Aug '11

Hi, the haddock information generated on hackage lists class instances per class and per data type e.g. on http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/Data-Eq.h… or http://hackage.haskell.org/packages/archive/xhtml/3000.2.0.1/doc/html/Text-… For some reason, the documentation generated on Debian does not. Does anybody have an idea why that could be? We use ./Setup haddock --hyperlink-source to build the documentation, using the haddock that is shipped with ghc (2.9.2 at the moment). Greetings, Joachim -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

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Re: [Haskell-cafe] Project Euler: request for comments
by KC 28 Aug '11

28 Aug '11

Think of the simplest version of the problem that isn't totally trivial. e.g. A one dimensional list of numbers. What would you do? Note: you only want to touch each element once. The 2 dimensional case could be handled by putting into lists: rows, columns, major diagonals, and minor diagonals. This isn't the fastest way of doing the problem but it has the advantage of avoiding "indexitis". On Fri, Aug 26, 2011 at 6:15 PM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > Like: > 20*19*21*18 > is bigger than > 100*100*3*2 > ? > > If so I need to think about how to formalize it. > > Thanks for the hint. > > On Fri, Aug 26, 2011 at 8:55 PM, KC <kc1956(a)gmail.com> wrote: >> Is Problem 11 the 4 consecutive #'s problem? >> >> If so what must be true for 4 #'s to have a large product? >> >> Hint: x * y * z * 2 is that going to be larger? >> >> -- >> -- >> Regards, >> KC >> > -- -- Regards, KC

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Modules and a main function
by michael rice 27 Aug '11

27 Aug '11

W/r/t the code below, would somebody please explain the sense of having a main function in a module that is not named Main.hs? Michael From: http://www.haskell.org/haskellwiki/State_Monad ============ module StateGame where import Control.Monad.State -- Example use of State monad -- Passes a string of dictionary {a,b,c} -- Game is to produce a number from the string. -- By default the game is off, a C toggles the -- game on and off. A 'a' gives +1 and a b gives -1. -- E.g -- 'ab' = 0 -- 'ca' = 1 -- 'cabca' = 0 -- State = game is on or off & current score -- = (Bool, Int) type GameValue = Int type GameState = (Bool, Int) playGame :: String -> State GameState GameValue playGame [] = do (_, score) <- get return score playGame (x:xs) = do (on, score) <- get case x of 'a' | on -> put (on, score + 1) 'b' | on -> put (on, score - 1) 'c' -> put (not on, score) _ -> put (on, score) playGame xs startState = (False, 0) main = print $ evalState (playGame "abcaaacbbcabbab") startState

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HJavaScript: representing build-in global function.
by Станислав Черничкин 27 Aug '11

27 Aug '11

Hi Cafe! Does someone know how to represent js build-in global function (such as parseInt(), parseFloat(), eval()) with HJavaScript? Perhaps JConst: JCall (JConst "parseInt") (JString "123")? -- Sincerely, Stanislav Chernichkin.

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Project Euler: request for comments
by Oscar Picasso 27 Aug '11

27 Aug '11

Hi, I order to improve my Haskell skills I started (again) to solve the project euler problems with this language. I am now at problem 11 and would really appreciate any comment about my code in order to make it more elegant or efficient. My solutions can be found here: http://fp.opicasso.com/tag/projecteuler Oscar Picasso

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Re: [Haskell-cafe] How to make callCC more dynamic
by oleg＠okmij.org 27 Aug '11

27 Aug '11

bob zhang wrote: > I thought the right type for ContT should be > newtype ContT m a = ContT {runContT :: forall r. (a-> m r) -> m r} > and > other control operators > shift :: Monad m => (forall r . (a-> ContT m r) -> ContT m r) -> ContT m a > reset :: Monad m => ContT m a -> ContT m a > callCC :: ((a-> (forall r . ContT m r)) -> ContT m a) -> ContT m a > unfortunately, I can not make callCC type check, and don't know how to > do it. Precisely that problem was discussed in http://okmij.org/ftp/continuations/undelimited.html#proper-contM Your ContT is CPS1 in the above article. The article shows why you cannot write callCC with the above type of ContT. The article talks about other types. BTW, if you faithfully defined the monad for undelimited control than shift/reset cannot be expressed. Undelimited continuations are strictly less expressible than delimited ones. The above page gives the pointers to the papers with the proof.

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