happstack | 易学教程

How to use “IO String” as an HTTP response in Happstack?

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问题 I'm retrieving data from a database using HDBC, then trying to send this data to a web client using Happstack. myFunc :: Integer -> IO String myFunc = ... fetch from db here ... handlers :: ServerPart Response handlers = do decodeBody (defaultBodyPolicy "/tmp/" 0 1000 1000) msum [ dir "getData" $ ok $ toResponse $ myFunc $ toInteger 1 ] mainFunc = simpleHTTP nullConf handlers When I build the above code I get this error: No instance for (ToMessage (IO String)) arising from a use of

Haskell Web Framework

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问题 I'm creating simple web application using haskell. First I used Snap in front and I was able to run the application, but I want to add user input to the application. I couldn't find a way to get user input parameters to the function. How might I do that? Other thing, I also used Happstack framework, I can not import "Happstack.Server". I use cabal installation configure Happstack. It was successfully installed, but when I try to import to "Happstack.Server", it gives me an error: <no location

cryptopp foreign library dependency

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问题 I tried to install happstack-server-tls package via cabal on Arch Linux (3.12.9), but got this error: Resolving dependencies... Configuring happstack-server-tls-7.1.0... Failed to install happstack-server-tls-7.1.0 Last 10 lines of the build log ( /home/boris/.cabal/logs/happstack-server-tls-7.1.0.log ): Configuring happstack-server-tls-7.1.0... /bin/sh: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8) setup-Cabal-1.16.0-x86_64-linux-ghc-7.6.3: Missing dependency on a foreign

How do I serve MathJax from a local Happstack server?

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问题 I'm not a developer/programmer. I'm just someone trying to use Gitit to take notes. I've got it to the point where it runs on Windows, but the math looks best using MathJax. I don't want to rely on a remote CDN to get the MathJax working (power cuts and internet disconnections are very frequent here). The author of the app mentions it can be setup in "4 lines of code" in Happstack: mathjax-script: https://d3eoax9i5htok0.cloudfront.net/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML #

Why can't a monad be decomposed?

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问题 I don't understand why I can't decompose a (let's say IO) monad. Like IO a -> a ? My question originated when using happstack and wanting to get the Text out of ServerPart (Maybe Text) which is returned by (optional $ lookText "domain") . Then I remembered reading that IO monad can't be escaped. I've read about unsafePerformIO and the reasons why it is bad, but none of those reasons seem to answer my question. 回答1: Can Monad s be escaped from? Yes. This is very easy with many Monad s, such as

How to host a Happstack website?

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问题 I've built a website using Happstack, but I have no experience in hosting. Everything I found online was either outdated or too complex for me. Is there an easy way, or tutorial I can follow to publish my Happstack website? Thanks 回答1: Here's a short overview of the hosting process I followed to get a website running using Haskell server software. Get a Server The first thing you need when you're hosting is a device to run the server code. You can either rent a "virtual computer" from a

Is there a good way to QuickCheck Happstack.State methods?

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问题 I have a set of Happstack.State MACID methods that I want to test using QuickCheck, but I'm having trouble figuring out the most elegant way to accomplish that. The problems I'm running into are: The only way to evaluate an Ev monad computation is in the IO monad via query or update . There's no way to create a purely in-memory MACID store; this is by design. Therefore, running things in the IO monad means there are temporary files to clean up after each test. There's no way to initialize a

How do I serve MathJax from a local Happstack server?

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I'm not a developer/programmer. I'm just someone trying to use Gitit to take notes. I've got it to the point where it runs on Windows, but the math looks best using MathJax. I don't want to rely on a remote CDN to get the MathJax working (power cuts and internet disconnections are very frequent here). The author of the app mentions it can be setup in "4 lines of code" in Happstack: mathjax-script: https://d3eoax9i5htok0.cloudfront.net/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML # specifies the path to MathJax rendering script. # You might want to use your own MathJax script to

Installing Haskell packages on Mac

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问题 I can't seem to get a few Haskell packages to install on my Mac (10.6.8). I first tried Happstack and it failed and then I tried Snap. Sometimes when I run ghci I get a segmentation fault. Other times it works and goes like this: GHCi, version 7.4.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> When trying to get Snap: .... .... .... Loading package