May 2010 - Haskell-Cafe

debugging a hanging program: where to start?
by Aran Donohue 13 May '10

13 May '10

Hi Cafe, I have a program that I can reliably cause to hang. It's concurrent using STM, so I think it could be a deadlock or related issue. I also do some IO, so I think it could be blocking in a system call. It only hangs when compiled with -threaded. I tried building with -prof, and running with -hc -xt to get a clue where in which function it is stopping, but the resulting profile didn't help much. I've started sprinkling print statements, but I thought I'd trawl for better tips and techniques. Any suggestions on approaches? Thanks, Aran

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Re: Frama-C
by Tom Hawkins 13 May '10

13 May '10

On Sun, May 9, 2010 at 12:54 AM, Lee Pike <leepike(a)gmail.com> wrote: > Tom, > >> Have you used any of these tools? They're pretty cool. I'd be >> interested to hear you opinion. >> >> http://frama-c.com/ > > Not yet. We were considering using them for a C security-analysis, but > rolled-our-own stuff in Haskell. Do you guys support ACSL or something similar? One major short comings of Frama-C is its inability to prove a formula false. As such, the tool will not return any counter examples to help with debugging. > > I'll ask around Galois if there's been any experience with it. > > Did anyone respond to your post about a Haskell interface? Negative. I'm looking into writing a bit of OCaml to dump out the Cil+ACSL stuff, which I can then read with Haskell. One thing I really like about Frama-C is its use of multiple solvers. Some work better than others, and it's very easy to see this in the gWhy GUI, as well as overall proof coverage. It would be nice to have a Haskell library where we could stream in a bunch of proof obligations and it would farm it out to different solvers, possibly running on different machines. It could also keep track of which obligations have proved true or false, so it doesn't wast time running the obligation on other solvers -- gWhy doesn't currently do this. You kind of alluded to these benefits when you recommended using SMT-LIB instead of Yices for AFV, but I didn't appreciated it until now. -Tom

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Data creation pattern?
by Eugene Dzhurinsky 13 May '10

13 May '10

Hello, all! I need to create objects like this data Object = MyObject { param1, param2, param3 :: String } from the input file param_1_param1=value11 param_2_param1=value21 param_2_param2=value22 param_1_param3=value13 param_2_param3=value23 param_1_param2=value12 so general pattern of recognizing parameter name and value is param_{id}_{property name}={property value} so I need to create function > parseDataFile :: [String] -> [Object] For now I can think on splitting the task into 2 functions > groupSameObjectParameters :: [String] -> [[String]] which will group the lines with same id into a list, and then apply function > createObject :: [String] -> Object so overall solution will be > parseDataFile :: [String] -> [Object] > parseDataFile = map createObject . groupSameObjectParameters however I have no neat idea about how to create instance of MyObject - I need to supply all of parameters to the constructor at once. Also I don't like the idea of rearranging list first and then create objects from another list, because the list can be relatively large. In imperative programming with mutable objects I would create an array, then for each line get the id and try to find if there is the object in the array at 'id' index. If no - create one. Then set appropriate property from value. Is it possible to do something similar in Haskell? Thank you in advance! -- Eugene N Dzhurinsky

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ANNOUNCE: yaml, data-object-yaml and data-object-json 0.3.0
by Michael Snoyman 13 May '10

13 May '10

Hi all, We're happy to announce the newest release of the three above packages. Notable changes include: * Anton Ageev wrote support for anchors and aliases into both the yaml and data-object-yaml package. * Anton also wrote support in data-object-yaml for merge keys. * The yaml package is now based on the iteratee package, replacing the previous cursor interface. This should hopefully make it easier to use, and perhaps more performant. * data-object-json API was modified to match (as much as possible) the data-object-yaml API. * In addition, there was a version bump for quite a number of the underlying libraries. Overall, data-object-yaml has not changed in any significant way for the user, and the data-object-json API changes should make it much more palatable. As always, feedback is welcome! Michael

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Major Emacs mode for reading GHC Core files
by Johan Tibell 13 May '10

13 May '10

Hi all, I wrote a minimal major mode for reading (and editing) GHC Core files. It provides syntax highlighting and removal of commonly ignored annotations, similar to what's offered by ghc-core. * Usage Dump the simplifier output in a file with a .hcr suffix: ghc -c -ddump-simpl -O2 Test.hs > /tmp/Test.hcr Open the .hcr file in Emacs. Use `ghc-core-clean-buffer` to remove commonly ignored annotations and namespace prefixes from the buffer. * Prerequisites You need to have haskell-mode installed. * Installation Download the file from http://johantibell.com/files/ghc-core.el and put it in your ~/.emacs.d directory. Add (load-file "~/.emacs.d/ghc-core.el") to ~/.emacs.d/init.el Cheers, Johan

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ANN: precis-0.3.1 - Cabal package diff tool
by Stephen Tetley 13 May '10

13 May '10

Hello all I've upload precis to Hackage - a diff tool for Cabal packages. It compares two cabal files looking at changes to the exposed and internal modules lists, then diffs the exposed modules. It only works on extant .hs files - i.e. it won't work on .hsc files. Also, I haven't tested if it works on .lhs files - parsing is left to haskell-src-exts. When it diffs new and old revisions of an exposed module it should report: - changes to the export list - changes to instance declarations - changes to exported data declarations - changes to the exported type signatures of exported functions The report it produces is not very pretty. A declaration is marked as *conflict* if its textual representation has changed - I compare the string output from pretty printing the new and old versions rather than look deeply into the AST. Though low-tech, this seems to work well in practice. I expect there are some bugs... Thanks to Malcolm Wallace for CppHs, and Niklas Broberg for haskell-src-exts. Best wishes Stephen

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corner case in Text.JSON 0.4.3
by Martin Hilbig 13 May '10

13 May '10

hi, since i got no answer from the maintainer, maybe someone else can take care of it, or at least point out, what i did wrong. so, i recently stumbled upon some error while using Text.JSON 0.4.3 [1]: Text/JSON/String.hs:(127,4)-(137,49): Non-exhaustive patterns in case indeed ghc warned: [5 of 7] Compiling Text.JSON.String ( Text/JSON/String.hs, dist/build/Text/JSON/String.o ) Text/JSON/String.hs:127:4: Warning: Pattern match(es) are non-exhaustive In a case alternative: Patterns not matched: [] from looking at the code i couldn't see how this would ever happen, but you can reproduce it be running the files from [2]: $ ./test < problem Ok (JSArray [JSString (JSONString {fromJSString = "this"}),JSString (JSONString {fromJSString = "is"}),JSString (JSONString {fromJSString = "some"}),JSString (JSONString {fromJSString = "json"}),JSObject (JSONObject {fromJSObject = [("that",JSString (JSONString {fromJSString = "works"}))]})]) test: Text/JSON/String.hs:(127,4)-(137,49): Non-exhaustive patterns in case the patch i put there fixes it (at least for me) to return an Error instead of dying: $ ./test < problem Ok (JSArray [JSString (JSONString {fromJSString = "this"}),JSString (JSONString {fromJSString = "is"}),JSString (JSONString {fromJSString = "some"}),JSString (JSONString {fromJSString = "json"}),JSObject (JSONObject {fromJSObject = [("that",JSString (JSONString {fromJSString = "works"}))]})]) Error "Unexpected end of String: does" Error "Malformed JSON: invalid token in this context not\"]" test: <stdin>: hGetLine: end of file have fun martin hilbig [1]: http://hackage.haskell.org/package/json [2]: http://friendpaste.com/3IvnChRMoczf0mIKpOtrYE

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Why is TChan GHC specific?
by Edward Amsden 12 May '10

12 May '10

I'm currently just getting into playing around with concurrency in haskell, primarily because I find STM intriguing. In looking through the docs I noticed that the transactional channels are GHC specific. http://hackage.haskell.org/packages/archive/stm/2.1.1.2/doc/html/Control-Co… I dug around the wiki and Google but I couldn't find the reason for this.

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ghc api renamed source
by Phyx 12 May '10

12 May '10

Hi all, I was wondering if it's possible to get to the renamed source before actually typechecking, I currently have parsed <- parse modName checked <- typecheckModule parsed let renamed = tm_renamed_source checked value = tm_typechecked_source checked but if typechecking failes, I get no information at all (an error), while I should be able to still get the renamed source. Any suggestions? Cheers, Phyx

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hSetEncoding on socket handles
by David Powell 12 May '10

12 May '10

Greetings, I am having trouble sending unicode characters as utf8 over a socket handle. Despite setting the encoding on the socket handle to utf8, it still seems to use some other encoding when writing to the socket. It works correctly when writing to stdout, but not to a socket handle. I am using ghc 6.12.1 and network-2.2.1.7. I can get it to work using System.IO.UTF8, but I was under the impression this was no longer necessary? I also don't seem to understand the interaction between hSetEncoding and hSetBinaryMode because if I set the binary mode to 'False' and the encoding to utf8 on the socket, then when writing to the socket the string seems to be truncated at the first non-ascii codepoint. Here is a test snippet, which can be used with netcat as a listening server (ie. nc -l 1234). > import System.IO > import Network > main = do > let a="λ" > s <- connectTo "127.0.0.1" (PortNumber 1234) > hSetEncoding s utf8 > hSetEncoding stdout utf8 > hPutStrLn s a > putStrLn a > hClose s Thanks, David

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