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ANN: cabal-dev 0.8
by Rogan Creswick 19 Jul '11

19 Jul '11

We're happy to announce the release of cabal-dev 0.8! This version is available on hackage now, and contains many bug fixes and improvements, as outlined in the full release notes below. --Rogan cabal-dev release 0.8 ================================================== The 0.8 release of `cabal-dev` fixes many of the bugs that have been reported by `cabal-dev` users. It also provides more flexible, easier configuration and improves tool support for working within the `cabal-dev` sandbox (ghc-pkg suport and better ghci support). Upgrading is recommended for all users. Please report any bugs or submit enhancement requests to <https://github.com/creswick/cabal-dev/issues>. Much of the work on this release (and previous releases) of `cabal-dev` was funded by Galois, Inc. <http://www.galois.com/> About cabal-dev ================================================== `cabal-dev` is a Haskell build tool that augments Cabal and cabal-install to make it convenient to work with a sandboxed set of packages. It limits the effect of your build on unrelated parts of your system. Among other things, `cabal-dev` satisfies the following needs: * Avoid conflicts between libraries by working only with the set of packages that are needed for the current project. * Enable depending on a patched dependency without that patched dependency accidentally being used by another project's build. * Enable the simultaneous development of multiple interdependent packages without the development versions leaking to other project build environments. Significant effort has been made to ensure that `cabal-dev` works across platforms (Mac, Windows, and Linux) and with the versions of GHC that are most commonly in use (6.10-7.0). What's new ================================================== Details can be found on github at <https://github.com/creswick/cabal-dev>. Bugs fixed: * `cabal-dev` no longer passes `--verbose` to cabal-install commands that do not accept it. <https://github.com/creswick/cabal-dev/issues/18> * `cabal-dev` now recognizes and passes through short flags to cabal-install. In particular, this bug frequently came up when attempting to pass a flag (`-f`) to `cabal-dev install`. <https://github.com/creswick/cabal-dev/issues/6> * `cabal-dev` now supports all cabal-install commands, including `test`. <https://github.com/creswick/cabal-dev/issues/10> * We also made changes that should address inconsistencies with the remote repository (Hackage) cache location, but those issues remain open until we have confirmation from end users (you!) that these changes actually fix those issues. <https://github.com/creswick/cabal-dev/issues/15> and <https://github.com/creswick/cabal-dev/issues/14> Enhancements and new features: * `cabal-dev ghci` now invokes ghci with the exact same set of flags that would be used in a cabal-install build (using a trick copied from Leksah). This means that it will now have the appropriate package visibility, language settings, and source directories set when it is invoked. Note that in order for `cabal-dev ghci` to work, all dependencies must already be installed in the sandbox, and the package must already be configured. * `cabal-dev buildopts` will print the set of build options that would be passed to GHC when invoking `cabal build`. You can then use these flags for other tools that invoke GHC (e.g. the doctest package <http://hackage.haskell.org/package/doctest>). * `cabal-dev ghc-pkg` will invoke `ghc-pkg` with the appropriate flags to examine or alter the package database inside the `cabal-dev` sandbox. * `cabal-dev` now has more flexible support for cabal-install configuration: * By default `cabal-dev` will now use any settings from your cabal-install configuration file, except those that must be overridden in order to sandbox the build. This makes it more convenient to e.g. use an alternate remote repository with `cabal-dev`. * `cabal-dev` now supports merging of additional cabal-install configuration settings, to make it easy to work with multiple cabal-install configurations (`--extra-config-file=...`). * `cabal-dev` now has a flag to pass explicit options to cabal-install in case there are any conflicts between `cabal-dev` flags (`--cabal-install-arg`). * `cabal-dev` now has a flag to specify a particular cabal-install executable to use (`--with-cabal-install=...`).

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I confused myself with generics, and now I confused ghc too
by Ari Rahikkala 19 Jul '11

19 Jul '11

I want to implement generic comparison on top of syb-with-class, and based on looking at syb, it seems I could base it on something like gzipWithQ from syb's Data.Generics.Twins. However, there's no Data.Generics.SYB.WithClass.Twins. So I set out to see if I can write one myself (well, one with just enough stuff to support gzipWithQ anyway) Here's what I've got so far: http://hpaste.org/49168 The problem is that GHCi seems to be somewhat confused, or at least confusing, about the type of gzipWithQ here. When I ask with :t, it reports the type as: gzipWithQ :: (Data ctx a2, Data ctx a3, Data ctx a) => Proxy ctx -> (forall a0. Data ctx a0 => a0 -> forall a1. Data ctx a1 => a1 -> r) -> a2 -> a3 -> [r] If I actually replace gzipWithQ's annotated type with this, GHCi will reject the program. And in any case with GenericQ being defined as "type GenericQ ctx r = Data ctx a => a -> r", isn't this closer to gzipWithQ's type with the type synonyms expanded? gzipWithQ :: forall ctx a r. Data ctx a => Proxy ctx -> (Data ctx a0 => a0 -> (Data ctx a1 => a1 -> r)) -> (Data ctx a2 => a2 -> (Data ctx a3 => a3 -> [r])) (GHCi accepts this as gzipWithQ's type so I assume it's the same one. I assume those class constraints after the => come with implicit foralls? Because it seems to mean the same thing if I put foralls in there) I have no idea how to even start figuring out how to make gzipWithQ and its type work. I only got this far by copying code from Data.Generics.Twins and passing down the proxy parameter and/or context type parameter (is it even possible for this approach to work?). What I can tell is that GHCi will still change the type like that even if gzipWithQ = undefined, so I'll have to change the type and not just the body of the function. Is this the kind of thing that all those newtypes in Data.Generics.Twins are for? Should I read up on type theory?

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Failure to install Network.CGI
by william murphy 19 Jul '11

19 Jul '11

Hi all, I tried to install the Network.CGI module by inputting: cabal install CGI into the terminal but got this error: Resolving dependencies... Configuring cgi-3001.1.8.2... Preprocessing library cgi-3001.1.8.2... Building cgi-3001.1.8.2... <command line>: cannot satisfy -package-id network-2.3.0.2-24fdc6b92867c7236e81708f93cae7d0 (use -v for more information) cabal: Error: some packages failed to install: cgi-3001.1.8.2 failed during the building phase. The exception was: ExitFailure 1 I'm almost positive I have the latest version of cabal, and have tried many things, but can't seem to see what I'm leaving out. Thanks, William

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How to use Yesod OAuth
by Haisheng Wu 18 Jul '11

18 Jul '11

Hello, I'm trying to use Yesod oAuth plugin to a SNS site which is very similar to Twitter. I add oAuth into the authPlugin and I'm able to see the auth URL at login page. I click the URL and it forwards me to a page ask me input that SNS site account. I fill in my account then the browser navigate to the authorize page display a authorised code (8 digits). Then, how I suppose to continue? (I think this is the 2nd phase of the oauth process) I expect there will be a text box in my App where I can fill in the authorised code. Or even the oAuth plugin automatically get the authorised code and continue to the next oauth phase. Appreciate your help! Haisheng

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Trying to make a calculator
by Emanuil Boyanov 18 Jul '11

18 Jul '11

Hi guys, I'm new to Haskell, I learn it for couple of months now and we've learned only simple functions like map, zip etc. But now my assignment is a lot tougher than I thought so I'll need some guidelines. I've googled my assignment and I saw a person with the exact assignment so I am gonna copy the task then I'm gonna show you what I've done so far. Here it is: Make calculator function. The function argument is a list of strings and also form such list, as each string of the argument made definite action. - If the string has the form of an arithmetic expression - calculate this expression. The string result becomes part of the list- result. If the expression contains a variable which is not assigned value, the result is displayed "undefined". - If the string has the form Name = value calculated from the last expression is assigned to the variable with the corresponding name in the list, and in the result list is formed a string with type name = ... where the site stands blank corresponding value. If there is not a calculated expression to be assigned to form a string "no value". - If the string is non-blank, but there is a species different from the above two case, form the string "error". - If the string is empty, incl. when it contains only spaces, in the result there is not form a string. Expressions consist of integers without sign variables, operations + (Addition), - (subtraction), * (multiplication) and / (divide) In the beginning, end or between the elements of each row can have spaces - they are irrelevant to its correctness. Example: the list-argument ["3 +7 / 2", "2 + x", "= s", "2 * s +4", "", "2 + +4 / 5"] function should provide a result-list ["6", "undefined", "s = 6", "16", "error"]. ========= So what I've done so far is: calculator [] = [] calculator [" "] = [] calculator [c] = [c] calculator (c:" ":cs) = c:calculator cs calculator (" ":cs) = calculator cs calculator (c:" ":" ":cs) = calculator (c:" ":cs) calculator (c:cs) | (head c `elem` ['a'..'z']) && (head(tail c) `elem` ['+','-','*','/']) && (last(take (length c-2)c) `elem` ['1','2','3','4','5','6','7','8','9']) = calculator cs | otherwise = "error":calculator cs I try at first to use pattern matching for the blank strings in the first list, so that I can get rid off them in the second list. Am I even on the right way here? I found the "elem" function and I'm trying to check if the first char of the string is a letter or a number, then if the second char is one of the operations and so on. Problem is that I have no idea how can I check if the variable is defined already or how to save a variable and then give that variable the new value - is that even possible? :] And another thing `elem` [1..9] isn't working - how can I make a single char of a string to hold an integer.. Could you give me some guidelines or at least tell me if I'm on the right way here so I can move forward and improve my program. Thanks a lot!

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ANNOUNCE: docidx-1.0.0
by Andy Gimblett 18 Jul '11

18 Jul '11

Hi all. I'd like to announce docidx, a new tool for Haskell documentation: http://hackage.haskell.org/package/docidx http://github.com/gimbo/docidx.hs docidx is a program which creates a static HTML page indexing your installed packages, with links to your local haddock docs and to each package's hackage page. It covers global and user packages, and handles multiple installed versions sensibly. Here's how the output looks: http://github.com/gimbo/docidx.hs/raw/master/examples/example.png The idea is to complement the "index by module name" which Cabal creates and maintains. Sometimes you want to find things by package. :-) (But note that unlike Cabal's index, docidx's isn't automatically updated when you install a new package; so, I run it once an hour from cron.) Please see the github page for more details, including customisation options. Hopefully somebody will find this useful. Maybe one day it could be part of cabal-install? :-) Thanks! -Andy PS: A bit of history/due credit: Martijn van Steenbergen did something similar in PHP in early 2009: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/53531/focus=53572 ; then I wrote a static version in Python later that year: http://gimbo.org.uk/blog/2009/09/23/ ; then Andy Price ported that to Haskell: https://github.com/andyprice/docidx.hs ; finally, I rewrote that to build the index via Cabal rather than walking the filesystem directly - and here we are. -- Andy Gimblett haskell(a)gimbo.org.uk

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Network.Html simpleTable fonts
by william murphy 18 Jul '11

18 Jul '11

How does one change the font and size of text in a cells in a simpleTable? As in, to change the height, one could state: x = simpleTable [] [height "5"] exampleTable Thanks, Will

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Why aren't files flushed at exit?
by Paul Johnson 18 Jul '11

18 Jul '11

If you open a file for writing and then exit with output unflushed, then Haskell does not flush the file for you. In ghci the program seems to work, but then when you compile it in ghc it mysteriously fails. I've just been bitten by this, but when I went to the bug tracker I found http://hackage.haskell.org/trac/ghc/ticket/4119 ticket 4119, which describes this behaviour and was resolved as "invalid". So presumably this behaviour is by design. Given that most environments get this right, why doesn't Haskell? Paul.

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Contacting Planet Haskell admins
by Michael Snoyman 17 Jul '11

17 Jul '11

Hi, I just sent an email to the Planet Haskell admins, and it bounced back. Apparently it's still forwarding to Don's old email address. Anyone able to update it? Michael

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Re: [Haskell-cafe] Haskell and Databases
by Greg Weber 17 Jul '11

17 Jul '11

Hi Tobias, Have you seen DSH [1]? You might also be interested in Persistent [2], but it sounds like it has different goals than what you are after. [1] http://hackage.haskell.org/package/DSH [2] http://www.yesodweb.com/book/persistent

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