March 2011 - Haskell-Cafe

WANTED: Compensated Haskell Hacker for Language Project
by Bryan Edds 29 Mar '11

29 Mar '11

Hello fellow Haskellers! I have a language I would like to prototype in Haskell. It's a 'language-oriented' programming language based on Lisp, ML, and Python. It's a relatively small language, but should be powerful enough to have many of its features implemented in terms of itself (classes, actors, almost all syntax, etc.) While the project is compensated, I'm just a commercial game programmer by day and don't have a corporate budget, so part of the motivation is the joy of the project itself. Otherwise, I have a budget of $4k - $6k USD over the next several months to compensate someone to hack it up for me. I don't have much in the way of specs, and the design is ongoing (almost certainly some holes), but there is an overview of the design here - http://channel9.msdn.com/Forums/Coffeehouse/Prototyping-New-Language-With-H… I really want to churn it out as a nice working concept to prove the language design and language oriented programming is practical even for soft-real time software like console games. The project will be open source throughout its development and the language will be free to use. I really want it to take off, despite my meager resources :) Beyond that, I'm looking for charitable investors once the prototype is finished and proven. I want to find other people are so sick of writing soft-real time software in C-family languages at their work place that it's worth the donation. Perhaps there is some company who might be interested in further incubating the project if it proves commercially interesting :) I do ask for the code to be reasonably clean as I would like to be able to help once I get some time. I would be implementing the thing fully myself, but I am way too swamped at work :) Since I have to rest my hands during my off hours, I would like to do most communication by voice. Feel free to record any of the communication if you like. If anyone is interested and has the credentials to bring the project to fruition, please contact me at bryanedds(a)yahoo.com straight away. Thanks!

3 3

How to best deal with nullPtr from alloca and friends?
by Jason Dagit 29 Mar '11

29 Mar '11

I was reading up on the documentation for alloca and friends[1], which says, "If any of the allocation functions fails, a value of nullPtr<http://www.haskell.org/ghc/docs/7.0.2/html/libraries/base-4.3.1.0/Foreign-P…> is produced." It seems like every example of FFI code that I find which uses alloca ignores the possibility of a nullPtr[2, 3, 4]. So then I started trying out examples with the help of dmwit and others from #haskell. It seems that actually, alloca and friends throw exceptions: dmwit> main = allocaArray (2^30) (\ptr -> print ((nullPtr :: Ptr Double) == ptr)) <dmwit> lispy: alloca also throws an exception. <dmwit> lispy: Or rather, allocaBytes throws an exception, and alloca is implemented in terms of allocaBytes, so I'm *guessing* that alloca throws an exception. I'm on a 64bit version of windows here with more than 4GB of memory to spare for the GHC process. Unfortunately, allocaBytes takes an Int so I can't test it with a request larger than the amount of physical ram I have. Just playing around with different arguments to allocaBytes I can get different behavior: <= 2^30 bytes, works perfectly == 2^30 + 2^20 bytes, I get an "<interactive>: out of memory" message and ghci terminates == 2^31-1, I get a crash where windows pops up a little dialog saying my program (ghci) has crashed. The behavior seems to be inconsistent with the documentation. What is the correct behavior for alloca and friends and should I be checking for nullPtr? Thanks, Jason [1] http://www.haskell.org/ghc/docs/7.0.2/html/libraries/base-4.3.1.0/Foreign-M… [2] http://en.wikibooks.org/wiki/Haskell/FFI [3] http://www.haskell.org/haskellwiki/HSFFIG/Examples [4] http://book.realworldhaskell.org/read/interfacing-with-c-the-ffi.html

2 3

ANN: improve-0.3.1
by Tom Hawkins 29 Mar '11

29 Mar '11

ImProve [1] is an imperative DSL for hard realtime embedded applications. ImProve programs are verified with infinite state,unbounded model checking (k-induction, invariant strengthening, SMT). In addition to C, ImProve now supports Simulink [2] as a backend target. Simulink is a popular language for automotive and aerospace control systems. -Tom [1] http://hackage.haskell.org/package/improve [2] http://www.mathworks.com/

1 0

Re: [Haskell-cafe] ANNOUNCE: enumerator 0.4.8
by Gregory Collins 29 Mar '11

29 Mar '11

On Mar 29, 2011 10:42 AM, <oleg(a)okmij.org> wrote: > > I'm keen to hear of the example that seem to require Iteratee's > allocating additional resources. I'd really like to see if any of such > cases can be cast it terms of regions, implemented via iterated > Iteratee transformers. Hello Oleg, The first example which comes to mind - because I recently implemented this - is HTTP uploads: the input stream can hold N files (the value of N not known ahead of time), and each upload can go to a separate temporary file. If the request stream fails early (e.g. client browser closes connection), any already-created temp files and any open file handles must be cleaned up.

1 0

Re: [Haskell-cafe] Iteratee, ghc 6.12/7.0 strange behaviour -epollControl: permission denied (Operation not permitted)
by Michael A Baikov 29 Mar '11

29 Mar '11

I tried with both 7.0.2 and 7.0.3 -----Original Message----- > On Mon, Mar 28, 2011 at 7:31 PM, Michael A Baikov <pacak(a)bk.ru> wrote: > > > > > > I am still playing with lastest iteratee and i think i found something strange. > > > > > > let's suppose we have a file test.hs like this: > > > > import Data.Iteratee > > import Data.Iteratee.IO > > import Data.Iteratee.Char > > > > main = fileDriver printLines "/etc/passwd" > > > > It works fine when executed via runhaskell / ghci in ghc 6.12. Compiled version in ghc 7 > > also works, but when i am trying to execute it via runhaskell / ghci i am getting this error: > > > > iter.hs: epollControl: permission denied (Operation not permitted) > > > > Any ideas? > > Make sure you have at least GHC 7.0.2. There were some I/O manager > bugs in 7.0.1. > > Johan >

2 1

working off a Yesod example file, need help lifting values from one monad into another. (and probably other things too).
by Michael Litchard 29 Mar '11

29 Mar '11

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 I'm working off of a example file from Yesod, ajax.lhs I've made an important change in types, and this has resulted in having to make the old code conform to the change. I will point out the specifics, then present my question. In the event I failed to include important information, I will paste in my code as well as the prototype. [Original] > getHomeR :: Handler () > getHomeR = do > Ajax pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first [Changed] > getHomeR :: Handler () > getHomeR = do > Tframe pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first Error Message test.lhs:62:4: Constructor `Tframe' should have 2 arguments, but has been given 1 In the pattern: Tframe pages In a stmt of a 'do' expression: Tframe pages <- getYesod **** This is not what I wrote ***** In the expression: do { Tframe pages <- getYesod; content <- widgetToPageContent widget; hamletToRepHtml (hamlet-0.7.1:Text.Hamlet.Quasi.toHamletValue (do { (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . preEscapedString) "<!DOCTYPE html><html><head><title>"; (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (Main.pageTitle content); .... })) } As far as I can tell, I only made a cosmetic change. I don't know what's going on here. [Original] > data Page = Page > { pageName :: String > , pageSlug :: String > , pageContent :: String ******** I'm going to change this ********** > } [Changed] > data Page = Page > { pageTitle :: String > , pageSlug :: String -- ^ used in the URL > , pageContent :: IO String ******** This is the change ******* > } Here's where I run into trouble [Original] > json page = jsonMap > [ ("name", jsonScalar $ pageName page) > , ("content", jsonScalar $ pageContent page) ******** I'm going to change this ******** > ] [My changes] > json page = jsonMap > [ ("name", jsonScalar $ Main.pageTitle page) > , ("content", jsonScalar $ liftIO $ pageContent page) ******* This is the change *********** > ] Here's the compiler error test.lhs:107:35: Couldn't match expected type `Char' against inferred type `[Char]' Expected type: String Inferred type: [String] In the second argument of `($)', namely `liftIO $ pageContent page' In the expression: jsonScalar $ liftIO $ pageContent page Failed, modules loaded: none. I'd appreciate a discussion about why this is wrong, and perhaps clues as to what is right. Last problem, stemming from the change in type to IO String. I don't have a clue as to what change I should make. test.lhs:100:25: No instance for (Text.Blaze.ToHtml (IO String)) arising from a use of `Text.Blaze.toHtml' at test.lhs:(100,25)-(103,3) Possible fix: add an instance declaration for (Text.Blaze.ToHtml (IO String)) In the second argument of `(.)', namely `Text.Blaze.toHtml' In a stmt of a 'do' expression: (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (pageContent page) In the first argument of `hamlet-0.7.1:Text.Hamlet.Quasi.toHamletValue', nam ely `do { (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . preEscapedString) "<h1>"; (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (Main.pageTitle page); (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . preEscapedString) "</h1><article>"; (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (pageContent page); .... }' And finally, both files can be found below, if it is necessary to look at them. [Original] <p>We're going to write a very simple AJAX application. It will be a simple site with a few pages and a navbar; when you have Javascript, clicking on the links will load the pages via AJAX. Otherwise, it will use static HTML.</p> <p>We're going to use jQuery for the Javascript, though anything would work just fine. Also, the AJAX responses will be served as JSON. Let's get started.</p> > {-# LANGUAGE ScopedTypeVariables, TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses #-} > import Yesod > import Yesod.Helpers.Static > import Data.Monoid (mempty) Like the blog example, we'll define some data first. > data Page = Page > { pageName :: String > , pageSlug :: String > , pageContent :: String > } > loadPages :: IO [Page] > loadPages = return > [ Page "Page 1" "page-1" "My first page" > , Page "Page 2" "page-2" "My second page" > , Page "Page 3" "page-3" "My third page" > ] loadPages :: IO [Page] loadPages = do > > data Ajax = Ajax > { ajaxPages :: [Page] > , ajaxStatic :: Static > } > type Handler = GHandler Ajax Ajax Next we'll generate a function for each file in our static folder. This way, we get a compiler warning when trying to using a file which does not exist. > staticFiles "static/yesod/ajax" Now the routes; we'll have a homepage, a pattern for the pages, and use a static subsite for the Javascript and CSS files. > mkYesod "Ajax" [$parseRoutes| > / HomeR GET > /page/#String PageR GET > /static StaticR Static ajaxStatic > |] <p>That third line there is the syntax for a subsite: Static is the datatype for the subsite argument; siteStatic returns the site itself (parse, render and dispatch functions); and ajaxStatic gets the subsite argument from the master argument.</p> <p>Now, we'll define the Yesod instance. We'll still use a dummy approot value, but we're also going to define a default layout.</p> > instance Yesod Ajax where > approot _ = "" > defaultLayout widget = do > Ajax pages _ <- getYesod > content <- widgetToPageContent widget > hamletToRepHtml [$hamlet| > \<!DOCTYPE html> > > <html> > <head> > <title>#{pageTitle content} > <link rel="stylesheet" href="@{StaticR style_css}"> > <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"> > <script src="@{StaticR script_js}"> > \^{pageHead content} > <body> > <ul id="navbar"> > $forall page <- pages > <li> > <a href="@{PageR (pageSlug page)}">#{pageName page} > <div id="content"> > \^{pageBody content} > |] <p>The Hamlet template refers to style_css and style_js; these were generated by the call to staticFiles above. There's nothing Yesod-specific about the <a href="/static/yesod/ajax/style.css">style.css</a> and <a href="/static/yesod/ajax/script.js">script.js</a> files, so I won't describe them here.</p> <p>Now we need our handler functions. We'll have the homepage simply redirect to the first page, so:</p> > getHomeR :: Handler () > getHomeR = do > Ajax pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first And now the cool part: a handler that returns either HTML or JSON data, depending on the request headers. > getPageR :: String -> Handler RepHtmlJson > getPageR slug = do > Ajax pages _ <- getYesod > case filter (\e -> pageSlug e == slug) pages of > [] -> notFound > page:_ -> defaultLayoutJson (do > setTitle $ string $ pageName page > addHamlet $ html page > ) (json page) > where > html page = [$hamlet| > <h1>#{pageName page} > <article>#{pageContent page} > |] > json page = jsonMap > [ ("name", jsonScalar $ pageName page) > , ("content", jsonScalar $ pageContent page) > ] <p>We first try and find the appropriate Page, returning a 404 if it's not there. We then use the applyLayoutJson function, which is really the heart of this example. It allows you an easy way to create responses that will be either HTML or JSON, and which use the default layout in the HTML responses. It takes four arguments: 1) the title of the HTML page, 2) some value, 3) a function from that value to a Hamlet value, and 4) a function from that value to a Json value.</p> <p>Under the scenes, the Json monad is really just using the Hamlet monad, so it gets all of the benefits thereof, namely interleaved IO and enumerator output. It is pretty straight-forward to generate JSON output by using the three functions jsonMap, jsonList and jsonMap. One thing to note: the input to jsonScalar must be HtmlContent; this helps avoid cross-site scripting attacks, by ensuring that any HTML entities will be escaped.</p> <p>And now our typical main function. We need two parameters to build our Ajax value: the pages, and the static loader. We'll load up from a local directory.</p> > main :: IO () > main = do > > pages <- loadPages > let s = static "static/yesod/ajax" > warpDebug 3000 $ Ajax pages s [My changes] > {-# LANGUAGE TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses > #-} > import Yesod > import Yesod.Helpers.Static > import System.Environment > import System.IO > import System.Directory > import System.FilePath.Posix > import Control.Applicative > import Data.List.Split > data Page = Page > { pageTitle :: String > , pageSlug :: String -- ^ used in the URL > , pageContent :: IO String > } > loadPage :: IO [Page] > loadPage = do > let directoryPath = "/home/mlitchard/playground/webTests/files" > let processedPath = map (directoryPath </>) . filter (`notElem` [".",".."]) > pageFileNames <- processedPath <$> getDirectoryContents directoryPath > let pageFiles = map readFile pageFileNames > return $ zipWith popEntries pageFileNames pageFiles -- > return $ zipWith popEntries > popEntries :: FilePath -> IO String -> Page > popEntries pageFileName pageFile = > let pageT = last $ splitOn "/" pageFileName > pageS = "Job" ++ pageT > in Page { Main.pageTitle=pageT, > pageSlug=pageS, > pageContent=pageFile } > data Tframe = Tframe > { tframePages :: [Page] > , tframeStatic :: Static > } > type Handler = GHandler Tframe Tframe > staticFiles "static/yesod/ajax" Routes > mkYesod "Tframe" [$parseRoutes| > / HomeR GET > /page/#String PageR GET > /static StaticR Static tframeStatic > |] defining the Yesod instance > instance Yesod Tframe where > approot _ = "" > defaultLayout widget = do > Tframe pages <- getYesod > content <- widgetToPageContent widget > hamletToRepHtml [$hamlet| > \<!DOCTYPE html> > > <html> > <head> > <title>#{Main.pageTitle content} > <link rel="stylesheet" href="@{StaticR style_css}"> > <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"> > <script src="@{StaticR script_js}"> > \^{pageHead content} > <body> > <ul id="navbar"> > $forall page <- pages > <li> > <a href="@{PageR (pageSlug page)}">#{Main.pageTitle page} > <div id="content"> > \^{pageBody content} > |] > getHomeR :: Handler () > getHomeR = do > Tframe pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first > getPageR :: String -> Handler RepHtmlJson > getPageR slug = do > Tframe pages _ <- getYesod > case filter (\e -> pageSlug e == slug) pages of > [] -> notFound > page:_ -> defaultLayoutJson (do > setTitle $ string $ Main.pageTitle page > addHamlet $ html page > ) (json page) > where > html page = [$hamlet| > <h1>#{Main.pageTitle page} > <article>#{pageContent page} > |] > json page = jsonMap > [ ("name", jsonScalar $ Main.pageTitle page) > , ("content", jsonScalar $ liftIO $ pageContent page) > ] > main :: IO () > main = do > > pages <- loadPage > let s = static "static/yesod/ajax" > warpDebug 3000 $ Tframe pages s If you've read to the bottom, thanks for your patience. I appreciate any illumination you can send my way. Michael

3 3

HsOpenSSL package fails to install
by Rob Nikander 28 Mar '11

28 Mar '11

Hi all, I tried `cabal install HsOpenSSL` and it died with some errors about 'i2d_of_void'. I'm on Mac OS X, gcc 4.2. The symbol 'i2d_of_void' is defined by a macro in the openssl/asn1.h header, which is indirectly included, so I don't see the problem. Any ideas? If this is a bug, is there a standard way to report it? Email the package maintainer in this case? thanks, Rob cbits/HsOpenSSL.c: In function ‘HsOpenSSL_DSAPublicKey_dup’: cbits/HsOpenSSL.c:220:0: error: ‘i2d_of_void’ undeclared (first use in this function) cbits/HsOpenSSL.c:220:0: error: (Each undeclared identifier is reported only once [... cascading errors from there ...]

1 0

Saving changes to cabal config in cabal-dev
by Yitzchak Gale 28 Mar '11

28 Mar '11

Thanks for the fantastic cabal-dev tool! Is there any convenient way to save changes to the package-specific cabal config file in cabal-dev? When I make changes to cabal-dev/cabal.config, cabal-dev seems to scribble over them next time I run it. The only solution I have found so far is to run cabal-dev install once (ignoring the errors) to create the cabal-dev directory and cabal.config, make a copy of cabal.config with a different name, edit it as needed, and then use a long-winded "--config=..." option for every subsequent run cabal-dev. The changes I need to make are as follows: - remote-repo-cache is wrong for Mac OS X - add more remote-repo lines for our local yackage servers. Note that the first is global, so it would be nice to have a way to make that change once globally for all packages. Whereas the second is, in general, package specific. We find local yackage servers much simpler to use and far more powerful than using add-source. You can organize packages by project, team, specific developers, etc. Thanks, Yitz

2 1

Iteratee, ghc 6.12/7.0 strange behaviour - epollControl: permission denied (Operation not permitted)
by Michael A Baikov 28 Mar '11

28 Mar '11

I am still playing with lastest iteratee and i think i found something strange. let's suppose we have a file test.hs like this: import Data.Iteratee import Data.Iteratee.IO import Data.Iteratee.Char main = fileDriver printLines "/etc/passwd" It works fine when executed via runhaskell / ghci in ghc 6.12. Compiled version in ghc 7 also works, but when i am trying to execute it via runhaskell / ghci i am getting this error: iter.hs: epollControl: permission denied (Operation not permitted) Any ideas?

2 1

bug in Prelude.words?
by malcolm.wallace 28 Mar '11

28 Mar '11

Does anyone else think it odd that Prelude.words will break a string at a non-breaking space? Prelude> words "abc def\xA0ghi" ["abc","def","ghi"] I would have expected this to be the obvious behaviour: Prelude> words "abc def\xA0ghi" ["abc","def\160ghi"] Regards, Malcolm

6 7