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 info>:
Could not find module `Happstack.Server':
it is not a module in the current program, or in any known package.
If I run my program using ghc --make HelloWorld.hs -v, I get:
Glasgow Haskell Compiler, Version 6.12.1, for Haskell 98, stage 2 booted by GHC version 6.12.1
Using binary package database: /usr/lib/ghc-6.12.1/package.conf.d/package.cache
Using binary package database: /home/udeshika/.ghc/i386-linux-6.12.1/package.conf.d/package.cache
package happstack-6.0.0-0f0c2507d590ebd01e8601c8667ec809 is unusable due to missing or recursive dependencies:
happstack-ixset-6.0.0-4e1b5476a551c4501c5734b22e0b280d happstack-server-6.0.3-6d71e7bb09489130538fb851a694b927 happstack-state-6.0.0-0e753e61d7092b6a5139e473113877a1 happstack-util-6.0.0-4156bd1331b7a0d62e0087101c9eba1c
package happstack-ixset-6.0.0-4e1b5476a551c4501c5734b22e0b280d is unusable due to missing or recursive dependencies:
happstack-util-6.0.0-4156bd1331b7a0d62e0087101c9eba1c
package happstack-server-6.0.3-6d71e7bb09489130538fb851a694b927 is unusable due to missing or recursive dependencies:
happstack-util-6.0.0-4156bd1331b7a0d62e0087101c9eba1c hslogger-1.1.4-90c801c802eec92e4e6a6f83d24d58d9 network-2.2.1.7-72dad7eb07ee7a683982f7475b8a449f network-bytestring-0.1.3.4-937fd511949a2d5ef21e86ec5306c791 sendfile-0.7.3-137cf51cc81a277d724637a7cd1e6b09
package happstack-state-6.0.0-0e753e61d7092b6a5139e473113877a1 is unusable due to missing or recursive dependencies:
happstack-util-6.0.0-4156bd1331b7a0d62e0087101c9eba1c hslogger-1.1.4-90c801c802eec92e4e6a6f83d24d58d9
package happstack-util-6.0.0-4156bd1331b7a0d62e0087101c9eba1c is unusable due to missing or recursive dependencies:
hslogger-1.1.4-90c801c802eec92e4e6a6f83d24d58d9 network-2.2.1.7-72dad7eb07ee7a683982f7475b8a449f
package hslogger-1.1.4-90c801c802eec92e4e6a6f83d24d58d9 is unusable due to missing or recursive dependencies:
...................
Snap's getParam function allows you to get HTTP request parameters specified by the user. These can come in the post body of a form submission or from the query string. For example, consider the following code:
site = dir "mypage" pageHandler
pageHandler = do
val <- getParam "foo"
writeBS $ maybe "no value" id val
If I request the url "myapp.com/mypage?foo=bar", then I will see "bar" as the response. If I leave off the "?foo=bar" part, then it will return "no value".
1) Check out that Happstack is actually installed and exposed:
ghc-pkg list | grep Happstack
2) What if you try to import Happstack.Server in ghci ?
3) Better use cabal-dev or capri for installing such things and making a sandbox
4) Snap and Yesod a quite new and they are under heavy development, Happstack is pretty
stable and solid.
5) What OS are you using? How did your installed the haskell? Ubuntu + haskell 6.12 + Happstack work out of the box
Regarding to the log, seems that cabal packages are messed up somehow. I recommend you to remove all packages from the .cabal and .ghc, reinstall cabal, then install cabal-dev as explained here:
http://www.reddit.com/r/haskell/comments/f3ykj/psa_use_cabaldev_to_solve_dependency_problems/
and then have fun with Happstack. Some guys actually use capri, it works as well.
Your installation is messed up. Unfortunately, cabal does that sometimes.
Your best bet is use 'ghc-pkg unregister ' to remove all the happstack packages, hslogger, and sendfile. Make sure they are removed from the user and global package databases. (ghc-pkg list will show you what is installed). Once you have the old versions removed, do, cabal update and the cabal install happstack. Then things should work.
What do you mean by 'user input' ? Do you mean html forms? Or something else ?
This section of the crash course may address your needs:
http://www.happstack.com/docs/crashcourse/RqData.html
It is also possible to use digestive-functors with Happstack to get type-safe form processing. Unfortunately, this is not well documented yet. Though I believe the disgestive-functors source code does include a working Happstack example.
Related
I wanted to get going with Haskell a little bit and therefore took a look at the Spock framework. To start clean, I uninstalled everything Haskell related from my Arch Linux machine and installed ghcup, Cabal and Stack using the install scripts from their respective websites.
Now I want to follow Spock's Tutorial. Trying to install Spock globally with cabal install Spock as suggested gives me an error (abbreviated):
src/Web/Spock/Internal/Wire.hs:43:1: error:
Could not find module ‘Web.Routing.AbstractRouter’
Use -v (or `:set -v` in ghci) to see a list of the files searched for.
|
43 | import Web.Routing.AbstractRouter
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cabal: Failed to build Spock-0.9.0.1. See the build log above for details.
I already found a question on reddit on the topic, but the solution does not apply because I'm not trying to use a specific version of the libraries as implied.
So I try to follow along and build only locally.
But when I reach the point where it says stack build --fast --pedantic, the build plan can not be constructed and Stack suggests to add another dependency, stm-containers. Doing so, I am presented with two additional suggestions for focus and primitive. When I add these, the plan fails again, this time without a simple solution:
In the dependencies for primitive-0.6.4.0:
base-4.13.0.0 from stack configuration does not match >=4.5 && <4.13 (latest matching version is 4.12.0.0)
needed due to Spock-example-0.1.0.0 -> primitive-0.6.4.0
I can do a little thing with Haskell, but with the build system(s), I am way out of my comfort zone. Help and hints appreciated. Oh, and all versions of course are the latest by the time of this post.
Due to incompatible versions of dependencies, Spock won't build with GHC 8.8 and above. A similar problem is described in Spock issue #149, though I'm not fully sure it is exactly the same incompatibility. The error you got from Stack hints at that, as base-4.13.0.0 is the version of base that is bundled with GHC 8.8. cabal-install failed in a more obscure way because, upon noting the incompatibility, it tries to solve the dependencies using older versions of Spock, eventually picking 0.9.0.1, attempting and, thanks to a missing version upper bound for the reroute dependency, failing to build it.
(Shortly after this answer was posted, the missing upper bound was retrofitted to the old Spock version, so attempting to reproduce the problem now will lead to an easier to understand failure.)
Casting the tutorial aside, the most straightforward way to use Spock given those complications is probably through cabal-install 3+. Begin by using ghcup to switch to GHC 8.6.5:
$ ghcup install 8.6.5
$ ghcup set 8.6.5
Then, create a blank project with cabal-install:
$ mkdir myproject
$ cd myproject
$ cabal init
Add Spock to the build-depends section of myproject.cabal:
build-depends: base >=4.12 && <4.13
, Spock == 0.13.*
Finally, you can run:
$ cabal build
Which will install Spock and its dependencies before building the project. (Note that you generally don't need to use cabal install to install libraries with cabal-install 3.)
It is presumably possible to make it work with Stack as well, by changing to the lts-14.27 resolver (the latest one that uses GHC 8.6.5), tracking down all dependency versions that need to be overriden (as you had began to do) and manually adding them to the extra-deps of stack.yaml.
I put this in a file (see bottom) and got the following error when loading it in ghci (i.e. start ghci then :l file):
7:13: error:
• Couldn't match expected type ‘network-uri-2.6.1.0#network-uri-2.6.1.0-7BN1tbB3iHQ2XgvmqLAYph:Network.URI.URI’
with actual type ‘Network.URI.URI’
NB: ‘Network.URI.URI’
is defined in ‘Network.URI’
in package ‘network-uri-2.6.1.0#network-uri-2.6.1.0-80FpvaNUTSDFCPv0sSze40’
‘network-uri-2.6.1.0#network-uri-2.6.1.0-7BN1tbB3iHQ2XgvmqLAYph:Network.URI.URI’
is defined in ‘Network.URI’
in package ‘network-uri-2.6.1.0#network-uri-2.6.1.0-7BN1tbB3iHQ2XgvmqLAYph’
Have I somehow installed two slightly different versions of network-uri, or what is this? How do I resolve it?
I've hardly used cabal but tried cabal install --reinstall network-uri, went fine but problem persists.
File contents:
import Network.HTTP
import Network.URI (parseURI)
import Data.Maybe (fromJust)
myRequestURL = "http://www.virginia.edu/cgi-local/ldapweb"
myRequest :: String -> Request_String
myRequest query = Request {
rqURI = fromJust $ parseURI myRequestURL
, rqMethod = POST
, rqHeaders = [ mkHeader HdrContentType "text/html"
, mkHeader HdrContentLength $ show $ length body ]
, rqBody = body
}
where body = "whitepages=" ++ query
main :: IO ()
main = do
response <- simpleHTTP $ myRequest "poon"
putStrLn ""
EDIT Re-installed haskell-platform. After this, ghc-pkg list reports all packages to be under (?) /usr/lib/ghc/package.conf.d, and the program I tried to copy loads just fine.
EDIT 2 After running cabal install some-pkg, ghc-pkg list reports that the newly installed stuff is in another directory. Indeed, ~/.cabal/config specifies install dirs for user, as well as install dirs for global. How is all this supposed to be managed properly?
GHC understands the concept of package databases. Cabal manages multiple package databases. There's a system package database, and a user package database. When you compile something with Cabal V1, it uses the union of these package databases. This is a bit of a time bomb, because, as you see, GHC does not like it when you have multiple of the same package. When you issued cabal install network-uri, cabal decided to install one copy of that package into your user database, though you already had one in the system database. When you tried to use ghc, it picked up on the two copies and got confused. Because cabal does not support removing packages, your Haskell installation was pretty much borked, and you reinstalled. I believe you could have done a more conservative rm ~/.ghc, or, had you been really adventurous, used the low-level ghc-pkg command to edit the package database.
Now that you've reinstalled the Platform, I would heavily recommend never using cabal install again. It's old, it's broken, cabal itself tells you not to use it. If you're using the Platform, I think it has stack in it, which is a different build manager, based on Cabal, which is not prone to this kind of breakage. Or, you can just stick to the V2 series of cabal commands, which is what I prefer.
Cabal V2 does not directly support your usecase, where you install a package globally and compile a program against it. This is because doing so is fundamentally broken: global package databases really just don't work for GHC. What Cabal V2 does is install packages into your home directory, ~/.cabal/store. You then have to explicitly tell it which packages you want, and it will construct a package database that contains each required package, without any wonkiness. You can get a REPL with a certain set of packages by issuing (this will take you to a temporary directory; you may need to :cd yourself back.)
cabal v2-repl -b network-uri -b package2 -b etc
If you want to actually compile files with ghc with a set packages, you have to actually define a package with a .cabal file. Here's a stub .cabal file:
name: temporary-pkg
version: 0.0.0.0
build-type: Simple
cabal-version: >=2.0
executable main -- if there is no Main, say "library" instead of "executable <name>"
default-language: Haskell2010
main-is: Main.hs -- only valid in executable stanzas
hs-source-dirs: src -- source files go here
build-depends: base, network-uri, package2, etc -- packages go here
Create and enter a directory, place that in temporary-pkg.cabal, place your sources in src/, and you can issue stuff like cabal v2-build and cabal v2-repl and cabal v2-exec main, etc. cabal will go off and install dependencies from Hackage into ~/.cabal/store as needed. cabal v2-install is therefore not that useful here. In general, v2-installing libraries is unnecessary, but v2-installing packages with executables is useful. Again, for hygiene reasons, you have to list all the packages you are importing from, but you don't need to list their dependencies or anything insane like that.
Cabal V2 still doesn't support uninstalling packages, though the point is that should not be necessary. However, if you find ~/.cabal/store getting too large for your liking, you can just nuke it, and should be built back up as packages are requested.
I'm trying to include a specific version of a library in a Haskell project. The library is bed-and-breakfast (which is used for martix operations), but I need the specific version 0.4.3 which fixed a bug with the multiplication implementation.
So, my stack.yaml looks like this:
flags: {}
extra-package-dbs: []
packages:
- .
extra-deps:
- bed-and-breakfast-0.4
- base-4.6.0.1
resolver: lts-12.8
But I'm getting this error when building:
Error: While constructing the build plan, the following exceptions were encountered:
In the dependencies for bed-and-breakfast-0.4:
base-4.11.1.0 from stack configuration does not match >=4.5 && <4.7 (latest matching version
is 4.6.0.1)
needed due to realworldhaskell-0.1.0.0 -> bed-and-breakfast-0.4
Some different approaches to resolving this:
* Set 'allow-newer: true' to ignore all version constraints and build anyway.
* Consider trying 'stack solver', which uses the cabal-install solver to attempt to find some
working build configuration. This can be convenient when dealing with many complicated
constraint errors, but results may be unpredictable.
* Recommended action: try adding the following to your extra-deps
in C:\Users\info\Desktop\Projects\haskell\stack.yaml:
- base-4.6.0.1
I've done the recommended action but it didn't solve anything. I've tried using different resolvers to see if it's an issue with my GHCi version but nothings worked. What is the best way to interpret error messages like this and how should I proceed?
EDIT:
If I remove -base.4.6.0.1 and add allow-newer: true I get this:
WARNING: Ignoring out of range dependency (allow-newer enabled): base-4.11.1.0. bed-and-breakfast requires: >=4.5 && <4.7
bed-and-breakfast-0.4: configure
Progress 1/2
-- While building custom Setup.hs for package bed-and-breakfast-0.4 using:
C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_2.2.0.1_ghc-8.4.3.exe --builddir=.stack-work\dist\7d103d30 configure --with-ghc=C:\Users\info\AppData\Local\Programs\stack\x86_64-windows\ghc-8.4.3\bin\ghc.EXE --with-g
hc-pkg=C:\Users\info\AppData\Local\Programs\stack\x86_64-windows\ghc-8.4.3\bin\ghc-pkg.EXE --user --package-db=clear --package-db=global --package-db=C:\sr\snapshots\76fd1958\pkgdb --package-db=C:\Users\info\Desktop\Projects\haskell\
.stack-work\install\8c390635\pkgdb --libdir=C:\Users\info\Desktop\Projects\haskell\.stack-work\install\8c390635\lib --bindir=C:\Users\info\Desktop\Projects\haskell\.stack-work\install\8c390635\bin --datadir=C:\Users\info\Desktop\Proj
ects\haskell\.stack-work\install\8c390635\share --libexecdir=C:\Users\info\Desktop\Projects\haskell\.stack-work\install\8c390635\libexec --sysconfdir=C:\Users\info\Desktop\Projects\haskell\.stack-work\install\8c390635\etc --docdir=C:
\Users\info\Desktop\Projects\haskell\.stack-work\install\8c390635\doc\bed-and-breakfast-0.4 --htmldir=C:\Users\info\Desktop\Projects\haskell\.stack-work\install\8c390635\doc\bed-and-breakfast-0.4 --haddockdir=C:\Users\info\Desktop\Pr
ojects\haskell\.stack-work\install\8c390635\doc\bed-and-breakfast-0.4 --dependency=array=array-0.5.2.0 --dependency=base=base-4.11.1.0 --dependency=binary=binary-0.8.5.1 --dependency=deepseq=deepseq-1.4.3.0 --dependency=template-hask
ell=template-haskell-2.13.0.0 --extra-include-dirs=C:\Users\info\AppData\Local\Programs\stack\x86_64-windows\msys2-20150512\mingw64\include --extra-lib-dirs=C:\Users\info\AppData\Local\Programs\stack\x86_64-windows\msys2-20150512\min
gw64\bin --extra-lib-dirs=C:\Users\info\AppData\Local\Programs\stack\x86_64-windows\msys2-20150512\mingw64\lib --exact-configuration
Process exited with code: ExitFailure 1
Logs have been written to: C:\Users\info\Desktop\Projects\haskell\.stack-work\logs\bed-and-breakfast-0.4.log
Configuring bed-and-breakfast-0.4...
Cabal-simple_Z6RU0evB_2.2.0.1_ghc-8.4.3.exe: The package has an impossible
version range for a dependency on an internal library: bed-and-breakfast
==0.3.2. This version range does not include the current package, and must be
removed as the current package's library will always be used.
EDIT 2:
Ok, so I'm guessing that the bed-and-breakfast library needs base 4.11.1.0 which is included in GHCi 6.10.2 (according to https://wiki.haskell.org/Base_package) so I need a resolver which matches that GHCi version. Where can I find out what resolver version that is?
Here is the constraint on the latest available bed-and-breakfast package: base (>=4.5 && <4.7), which means it will likely not even compile with GHC version higher then 7.6. Considering that there is even no LTS snapshot prior to GHC 7.8, you are out of luck with that package.
To say it in another words, the package is outdated and your choices are:
submit an issue and hope maintainer will do something about it
try to make it work with newer ghc yourself
Use a different package
I am attempting to install the code for "Haskell: The Craft of Functional Programming", 3rd edition.
I'm using GHCi, version 7.6.3 on Centos version 7.
Then:
cabal unpack Craft3e
cd Craft3e-0.1.1.0/
cabal install
...
[29 of 67] Compiling CalcParseLib ( Calculator/CalcParseLib.hs, dist/build/CalcParseLib.o )
Calculator/CalcParseLib.hs:132:10:
Not in scope: type constructor or class `Applicative'
Failed to install Craft3e-0.1.1.0
cabal: Error: some packages failed to install:
Craft3e-0.1.1.0 failed during the building phase. The exception was:
ExitFailure 1
I have attempted this installation multiple times, but cannot
overcome this error.
Could I use something other than "cabal install"?
I have plenty to learn about Haskell before I get to this example,
but it would be great to know the installation is fine! :)
You have three options:
Install an older version of the Craft3e package, with e.g. cabal unpack Craft3e-0.1.0.10.
Find Calculator/CalcParseLib.hs in the source files you have downloaded with cabal unpack and add a...
import Control.Applicative
... line next to the other import lines at the beginning. I suspect you will have to do the same with other modules, if the same error shows up elsewhere after you do this change, and there might be other issues of a similar nature.
Install a newer version of GHC (7.6.3 is from 2013). Though the default CentOS repositories won't offer that, there are other options, such as an unofficial Fedora repository and a manual installation. See this page for instructions.
#3 is the definitive solution. If you just want to get started with the book right now, though, you can go for #1 and leave the reinstall for later.
For the sake of reference, here is a brief explanation of the problem (I will use some unfamiliar terms, but you will soon enough learn about them as you study Haskell). There is an important type class called Applicative which, for historical reasons, wasn't as well integrated with the rest of the core libraries as it should be. This situation was corrected in GHC 7.10, which both included Applicative in the Prelude (the module which is imported by default in Haskell programs) and made it necessary to add Applicative instances in a number of places where they were missing. The code in the Craft3e package was updated so that these Applicative instances were in place (cf. this entry in the book's blog), but the import Control.Applicative line, which would be necessary to make the updated code work in older GHCs that do not have Applicative in the Prelude, wasn't added, leading to the error that you are seeing.
I'm trying to use http://hackage.haskell.org/package/persistent-1.2.3.0, but after installing it through "cabal install persistent", ghc doesn't find its exposed-modules:
Prelude> import Database.Persist.Types
<no location info>:
Could not find module `Database.Persist.Types'
It is not a module in the current program, or in any known package.
And ghc-pkg works fine:
$ ghc-pkg find-module Database.Persist.Types
/var/lib/ghc/package.conf.d
/home/apsk/.ghc/x86_64-linux-7.6.3/package.conf.d
persistent-1.2.3.0
Am I missing something or is this just a bug with cabal/persistent/ghc? My ghc is 7.6.3, btw.
Also, I've tried with no effect: "ghc-pkg recache"; "ghc-pkg check"; installing previous version; reinstalling with and without "sudo" and/or "--global".
Check that you're not using sandboxes, cabal-dev, hsenv, anything else that can influence ghc in looking for dependencies. Make sure you're using ghc/ghci, and not any wrappers, and that ghc/ghci are not aliased to anything in your shell.
Try to specify the package-db explicitly:
ghci -package-db /home/apsk/.ghc/x86_64-linux-7.6.3/package.conf.d
If you launch ghci with -v, it'll print the (caches of) databases it looks at, like this:
% ghci -v
GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help
Glasgow Haskell Compiler, Version 7.6.3, stage 2 booted by GHC version 7.4.2
Using binary package database: /opt/ghc763/lib/ghc-7.6.3/package.conf.d/package.cache
Using binary package database: /home/feuerbach/.ghc/i386-linux-7.6.3/package.conf.d/package.cache
Make sure that the database which has persistent is listed there.
Hopefully helpful to someone. Using ghci -v I looked to see if persistent was there, and saw this:
package persistent-2.0.8-cec952b1a61645f47dbec3b0b0cbcef4 is unusable due to missing or recursive dependencies: aeson-0.8.0.0-1bd8b5254a1dd30c0fe6acc346ad7de7 attoparsec-0.12.1.2-48393fcdbcf426085b696dc4409d9270 conduit-1.2.0.2-39f9cd0430ed7b7f4306899cbeb1ed83 monad-logger-0.3.7.2-3e6a80e9b3adf31497ff04514bdf2919 resource-pool-0.2.3.0-c02186641e7173f72887d5e65a646ac1 scientific-0.3.3.1-13e0eefbd7215e4503420c3d0a6fdb82 unordered-containers-0.2.5.0-147c3bb8f4a2da7d753455e75af30b92
So I looked around on SO (saw this: Haskell Cabal: Mysterious missing or recursive dependencies) but didn't find a great answer. I did find a good one here though:
$ ghc-pkg list Cabal
Which revealed I had 2 goddamn cabals! One in user and one in global. Ugh. So I was able to do ghc-pkg unregister --user Cabal-1.18.1.3 --force to get rid of the old one. Then cabal install cabal automatically went for 1.20, implicitly into user without any flag (the alternate would be --global).
The problem only occurs in GHCi, right? Have you restarted GHCi since installing persistent? (Maybe there's another way to get GHCi to pick up newly installed packages, but I'm not aware of it.