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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 17 Jul '11

17 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 17 Jul '11

17 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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Constructor discipline and dependent types.
by Patrick Browne 17 Jul '11

17 Jul '11

Hi, My understanding of the constructor discipline (CD) is that it is a restriction on the form of an equation that guarantees that the equation represents an executable function. The CD restricts the LHS of an equation to consist of a function name, constructors, and variables. Also there should be no new variables on the RHS. So CD permits function to be defined and prohibits general assertions which are more in the domain of a specification language. Question 1: Is the above a reasonable understanding of CD? Question 2: I have read that the lack of dependent types (DT) prevents writing general assertions in Haskell. Is CD related to DT? If so how are they related? Regards, Pat This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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Animas/Yampa: ArrowChoice?
by Ertugrul Soeylemez 16 Jul '11

16 Jul '11

Hello all, I really like the way Animas (fork of Yampa) represents reactive systems, and I would love to write some of my simulations using it. Unfortunately most of what I want to do requires dynamic systems, which can be boiled down to me believing to need an ArrowChoice instance for the SF arrow, because I have to choose between different signal paths depending on the input signal or events. Animas appears to be only suitable for robot-like systems with specific, predefined actors. Is there anything I can do about it? Is it difficult to write the ArrowChoice instance? Or is there a different solution, which I overlooked? Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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urWeb, Haskell and dependent types ....
by Vasili I. Galchin 16 Jul '11

16 Jul '11

Hello, Here is probably a good paper to get people up to speed on dependent types (ironically written by two contributors to this mailing list??): okmij.org/ftp/papers/lightweight-static-capabilities.pdf Vasili

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