- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Dynamically typing TH.Exp at runtime
by Martin Hofmann 16 Mar '09

16 Mar '09

Sorry, maybe it I didn't made it clear enough. > Perhaps I'm misunderstanding something, but since one can infer types > in GHCI, that implies one can infer types in the GHC API; since Hint > wraps the GHC API, that implies one can infer types in Hint, doesn't > it? And indeed, there are functions to infer the type of a String; > iirc I've even used them myself in mueval. > That's true, inferring the type of a string is not the problem. However, I am not only interested in the top-level type, but also in the type of any arbitrary subexpression. Consider for example following recursive definition: foo [] = [] foo (x:xs) = (:)(x+1)(foo xs) Typing only the first rule one would says its type is '[a] -> [a]'. However, the second rule specialises the type to 'Num a => [a] -> [a]'. So, if I am interested in the type of the 'x' in the pattern of the second rule, I need to be aware of its binding on the right-hand side. Consequently the type of 'x' is 'Num a'. AFAIK, I need Hendley-Milner type inference for that (please correct me if I am wrong) and I was wondering if I really need to implement it by myself, when it is already somewhere inside GHC. Thanks, Martin

3 6

examples for error handling in takusen?
by Gü?nther Schmidt 16 Mar '09

16 Mar '09

Hi, can someone please point me to error handling examples with takusen? I try to run a piece of code with takusen but just get the very sparse "Database.InternalEnumerator.DBException

2 1

A new haskell tools project
by L.Guo 16 Mar '09

16 Mar '09

Hi all: I have just created an haskell work toolset project in google code. Currently there are only a few tools to process YUV image files I wrote before. Welcome you attend in to improve my code or to add in your tools. And also pleasure to get your advices. http://code.google.com/p/haskellworkingtools/ Regards -------------- L.Guo 2009-03-16

1 0

Re: is there a version of hsffig that builds on a recent versin of haskell?
by Dmitry Golubovsky 16 Mar '09

16 Mar '09

On Mar 15, 4:03 am, Anatoly Yakovenko <aeyakove...@gmail.com> wrote: > is there a version of hsffig that builds on a recent versin of haskell? > _______________________________________________ > Haskell-Cafe mailing list > Haskell-C...@haskell.orghttp://www.haskell.org/mailman/listinfo/haskell-cafe Unfortunately no. There have been too many changes in GCC and GHC since, and too low interest to the project from other developers, so I did not maintain it. Dmitry.

2 1

Most elegant funciton for removing adjacent duplicates from a list using foldl and foldr
by R J 16 Mar '09

16 Mar '09

I need to write an implementation using foldl, and a separate implementation using foldr, of a function, "remdups xs", that removes adjacent duplicate items from the list xs. For example, remdups [1,2,2,3,3,3,1,1]= [1,2,3,1]. My approach is first to write a direct recursion, as follows: remdups :: (Eq a) => [a] -> [a] remdups [] = [] remdups (x : []) = [x] remdups (x : xx : xs) = if x == xx then remdups (x : xs) else x : remdups (xx : xs) This code works, but it has three cases, not usual two, namely [] and (x : xs). What, if any, is the implementation using only two cases? Also, if three cases are required, then how can it be implemented using foldr, and how using foldl? Thanks. _________________________________________________________________ Express your personality in color! Preview and select themes for Hotmail®. http://www.windowslive-hotmail.com/LearnMore/personalize.aspx?ocid=TXT_MSGT…

5 4

Help with Bird problem 4.5.6: sequence of successive maxima
by R J 16 Mar '09

16 Mar '09

This Bird problem vexes me, in the first instance because it doesn't seem to specify a unique solution: Given a list xs = [x_1, x_2, . . . , x_n], the sequence of successive maxima "ssm xs" is the longest subsequence [x_j1, x_j2, x_j3..x_jk] such that j_1 = 1 and j_m < j_n => x_jm < x_jn. For example, xs = [3, 1, 3, 4, 9, 2, 10, 7] => ssm xs = [3, 4, 9, 10]. Define "ssm" in terms of "foldl". >From this specification, I infer: ssm [] = [] ssm [1] = [1] ssm [1, 2, 3] = [1, 2, 3] ssm [1, 0, 3, 2] = [1, 3] However, what is ssm [1,0,100,2,3,4,5]? Is it [1, 100] or [1, 2, 3, 4, 5]? I think the latter, but am not certain. Whichever it is, what's the solution? Thanks. _________________________________________________________________ Windows Live™ Groups: Create an online spot for your favorite groups to meet. http://windowslive.com/online/groups?ocid=TXT_TAGLM_WL_groups_032009

3 3

State monad is missing Applicative instance
by Peter Verswyvelen 15 Mar '09

15 Mar '09

I think. Or is it defined in some other package?

7 9

big discussion about Haskell on Reddit
by FFT 15 Mar '09

15 Mar '09

I noticed that on Programming Reddit, where I lurk, there is a big discussion about the disconnect between how much Haskell is advocated there and the number of applications written in it. http://www.reddit.com/r/programming/comments/84sqt/dear_reddit_i_am_seeing_… The difficulty of reasoning about memory and CPU-efficiency in nontrivial programs was suggested as an explanation.

2 1

I can't install hs-plugins beceause of Linker.h
by Yuri Kashnikoff 15 Mar '09

15 Mar '09

Hi! I was trying to install hs-plugins both from sources "$./Setup.lhs ..." and with "$cabal fetch&&cabal install" and both failed. It always reports that Linker.h is missing. I have tried to use --extra-include-dirs with path to ghc-6.10.1 dir and ghc-6.10.1/include dir. Nothing changed. Here is a report from Setup.lhs: Setup.lhs:2:2: Warning: In the use of `defaultUserHooks' (imported from Distribution.Simple): Deprecated: "Use simpleUserHooks or autoconfUserHooks, unless you need Cabal-1.2 compatibility in which case you must stick with defaultUserHooks" Warning: defaultUserHooks in Setup script is deprecated. Configuring plugins-1.4.0... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package ghc-6.10.1 requires Cabal-1.6.0.1 package plugins-1.4.0 requires Cabal-1.6.0.2 checking build system type... i386-apple-darwin9.6.0 checking for ghc... ghc checking for value of __GLASGOW_HASKELL__... 610 checking for ghc library directory... /opt/local/lib/ghc-6.10.1/. checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ANSI C... none needed checking for arc4random... yes checking for a BSD-compatible install... /usr/bin/install -c configure: creating ./config.status config.status: creating config.mk config.status: creating testsuite/makewith/io/TestIO.conf config.status: creating testsuite/makewith/unsafeio/Unsafe.conf config.status: creating config.h config.status: config.h is unchanged Setup.lhs: Missing dependency on a foreign library: * Missing header file: Linker.h This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. -- Yuri S. Kashnikov Novosibirsk State University, Russia 2 Pirogova street 630090, Novosibirsk-90 yuri.kashnikoff(a)gmail.com

4 6

Link errors
by Lingappan, Loganathan 15 Mar '09

15 Mar '09

Hi, If I include import Text.Regex.Posix ((=~)) into a Haskell code, I get the following link error: FindBBUsage.o:fake:(.text+0x44d): undefined reference to `__stginit_regexzmposixzm0zi72zi0zi3_TextziRegexziPosix_' collect2: ld returned 1 exit status Any ideas on how to fix this? I am using GHC version 6.10.1 on Windows XP. Thanks, Logo

2 1