Suppose I have a library packaged and built using Cabal, and some module Internal is not in my cabal file's Exposed-modules. Does it then make any difference if I specify a pragma
{-# OPTIONS_HADDOCK hide #-}
at the top of Internal.hs, or is it already automatically hidden according to Haddock?
If it does make a difference, what effect does it have?
It does make a difference if the haddocks of the package are created with the --internal flag to cabal haddock.
$ cabal help haddock
Usage: cabal haddock [FLAGS]
Flags for haddock:
-h --help Show this help text
-v --verbose[=n] Control verbosity (n is 0--3, default verbosity
level is 1)
<snip>
--executables Run haddock for Executables targets
--internal Run haddock for internal modules and include all
symbols
<snip>
If the haddocks are created without the --internal flag, the hide module attribute has no effect: no documentation is created for the module anyway.
If --internal is given, then documentation is created for non-exposed modules except those that specify the hide attribute.
In other words, documentation is generated if hide is not set and either --internal is specified or the module is exported.
The use of --internal for cabal haddock can be specified with cabal install --haddock-internal, or when manually invoking cabal haddock, or with the runhaskell ./Setup.hs ... interface.
Most people just run cabal install with the default options, so only few would observe the difference.
Related
I installed the timezone-series Haskell module using cabal install timezone-series-0.1.5.1.
I then defined a module named Main.hs that starts with:
import Data.Time.LocalTime.TimeZone.Series -- from timezone-series-0.1.5.1
when I run ghc Main.hs, GHC throws the following error:
/home/ubuntu/Main.hs:2:1: error:
Failed to load interface for ‘Data.Time.LocalTime.TimeZone.Olson’
I tried explicitly including the cabal directory in GHC's search path using:
ghc -i/home/ubuntu/.cabal/lib/x86_64-linux-ghc-8.0.2/timezone-olson-0.2.0-KqRNJj3zomR7zz2Yx6P5Oq/ Main.hs
This resulted in the correct path being searched, but GHC is only looking for files ending in the suffix ".hs":
Locations searched:
...
/home/ubuntu/.cabal/lib/x86_64-linux-ghc-8.0.2/timezone-olson-0.2.0-KqRNJj3zomR7zz2Yx6P5Oq/Data/Time/LocalTime/TimeZone/Series.hs
/home/ubuntu/.cabal/lib/x86_64-linux-ghc-8.0.2/timezone-olson-0.2.0-KqRNJj3zomR7zz2Yx6P5Oq/Data/Time/LocalTime/TimeZone/Series.lhs
/home/ubuntu/.cabal/lib/x86_64-linux-ghc-8.0.2/timezone-olson-0.2.0-KqRNJj3zomR7zz2Yx6P5Oq/Data/Time/LocalTime/TimeZone/Series.hsig
/home/ubuntu/.cabal/lib/x86_64-linux-ghc-8.0.2/timezone-olson-0.2.0-KqRNJj3zomR7zz2Yx6P5Oq/Data/Time/LocalTime/TimeZone/Series.lhsig
Cabal installed interface files instead however:
/home/ubuntu/.cabal/lib/x86_64-linux-ghc-8.0.2/timezone-olson-0.2.0-KqRNJj3zomR7zz2Yx6P5Oq/Data/Time/LocalTime/TimeZone/Olson.hi
From line 318 of GHC's source code it looks like GHC ignores "*.hi" files unless it is called in single-shot mode (with the -c flag). Is this correct? (See: https://github.com/ghc/ghc/blob/67a5a91ef5e61f3b3c84481d8a396ed48cd5d96e/compiler/GHC/Unit/Finder.hs)
How can I get GHC to import this module?
An help will be greatly appreciated!
My suggested ways of installing packages in order of my preference:
Make a cabal package and add timezone-series you want to install to the build-depends field as described in the cabal manual.
Use the experimental cabal-env tool to basically automate the process of point 3 below, but then with the global environment. This makes a new build-plan every time you install a new package, so it is like removing the package environment and building it again with all the old packages and the new package added to it. You can add specific constraints like this: cabal-env "timezone-series == 0.1.5.1".
Install a package into local package environment with cabal --package-env . --lib timezone-series. You can add as many packages as you want after the --lib option to install more than one package. If you later want to use a different set of packages simply remove the .ghc.environment.* file that is generated and rerun the installation with a new set of packages. GHC will automatically use these package environment files that are in the current or parent directories. You can specify specific constraints with the --constraint option like this: --constraint "timezone-series == 0.1.5.1".
Use cabal install --lib timezone-series to install it directly into the global environment (~/.ghc/x86_64-linux-8.0.2/environments/default), this will fail if a conflicting package was installed earlier. When you run into errors you can remove that package environment and try again.
Finally, I want to note that GHC 8.0.2 is quite old, so I would advise you to upgrade if you don't have a specific reason for using that version.
I'm getting an error that says the module doesn't exist when I try to runhaskell. It's odd because I try to install it first and says its up to date. Any idea how to fix this?
You could try creating the package environment in the local directory that holds your project, like this:
c:\Users\...\ex1haskell> cabal install --lib --package-env . QuickCheck
This should create a file of the form .ghc.environment.xxx in ex1haskell, which hopefully should be picked up by runhaskell/ghci/ghc invocations.
In ghci sessions, a sign that the environment is being picked up is the following message while starting:
Loaded package environment from ...
When the --package-env location is not given explicitly, a default location is used. According to the docs:
By default, it is writing to the global environment in
~/.ghc/$ARCH-$OS-$GHCVER/environments/default. v2-install provides the
--package-env flag to control which of these environments is modified.
But it seems that runhaskell is having problems to find the environment file in that default location.
Note. When creating a package environment, it's possible to specify multiple packages simultaneously, like this:
cabal install --lib --package-env . QuickCheck random aeson transformers
Also, package environments are just text files, so local environments can be deleted and recreated at will. The actual package binaries reside elsewhere and can potentially be reused by cabal.
A Common Environment
It is hard to debug if/when the actual tooling differs so let's first get a unified setup. I'll use docker to get GHC 8 and Cabal 3.x:
docker run --rm -it haskell bash
Understand that this isn't arbitrary or even preemptive. What you have shown - cabal install --lib ... and runhaskell ... does work for sane tool installations. You might have a bad installation or an old version of a tool that has different behavior.
Running a single file with runhaskell
Now we need a project:
root#8a934c302dba:/# mkdir Ex1
root#8a934c302dba:/# cd Ex1
root#8a934c302dba:/Ex1# cat <<EOF >Main.hs
> import Test.QuickCheck
>
> main :: IO ()
> main = print =<< (generate arbitrary :: IO Int)
> EOF
And test failure:
root#8a934c302dba:/Ex1# runhaskell Main.hs
Main.hs:1:1: error:
Could not find module `Test.QuickCheck'
Use -v (or `:set -v` in ghci) to see a list of the files searched for.
|
1 | import Test.QuickCheck
And install the library:
root#8a934c302dba:/Ex1# cabal update && cabal install --lib QuickCheck
And successful run:
root#8a934c302dba:/Ex1# runhaskell Main.hs
15
So my comment above was wrong - we don't need to explicitly list the package as it is already exposed after installation.
I have been trying to run a simple Haskell program using TDFA. The program is as follows:
import Control.Monad
import Data.Array
import qualified Data.Text as T
import Text.Regex
import Text.Regex.TDFA
import Text.Regex.Base
str = "abbbbaab" :: String
regex = "(a+)(b+)" :: String
main = do
if str (=~) :: regex then putStrLn "matched" else putStrLn "no matches"
when I try to run the above program using the command like: ghc test.hs -o test and then I am getting the following error (test.hs is the Haskell program which contains the above code):
Text/Regex/TDFA/NewDFA/Engine.hs:13:33: parse error on input ‘#’
Note that I have the latest version of TDFA installed on my pc. I did it by following ways:
ghc --make -o setup Setup.hs
Also, I did the following:
user#user-VirtualBox:~/regex-tdfa-master$ sudo cabal install regex-tdfa
[sudo] password for user:
Resolving dependencies...
All the requested packages are already installed:
regex-tdfa-1.2.2
Use --reinstall if you want to reinstall anyway.
I even tried it with the Makefile which I got from TDFA's github repository:
user#user-VirtualBox:~/regex-tdfa-master$ make
ghc -o setup --make ./Setup.hs
./setup clean
cleaning...
./setup configure --prefix=/Users/user/local/devel/trl --enable-library-profiling --user
Configuring regex-tdfa-1.2.2...
./setup build
Building regex-tdfa-1.2.2...
Preprocessing` library regex-tdfa-1.2.2...
[ 1 of 23] Compiling Text.Regex.TDFA.NewDFA.Uncons ( Text/Regex/TDFA/NewDFA/Uncons.hs, dist/build/Text/Regex/TDFA/NewDFA/Uncons.o )
...........(Skipped to make the things short here)..............................
[23 of 23] Compiling Text.Regex.TDFA ( Text/Regex/TDFA.hs, dist/build/Text/Regex/TDFA.o )
Text/Regex/TDFA.hs:60:8:
Could not find module ‘Text.Regex.Base’
Perhaps you haven't installed the profiling libraries for package ‘regex-base-0.93.2#regex_47KXx9dLqeO8MNJeizLKhP’?
Use -v to see a list of the files searched for.
Text/Regex/TDFA/ByteString.hs:24:8:
Could not find module ‘Text.Regex.Base.Impl’
Perhaps you haven't installed the profiling libraries for package ‘regex-base-0.93.2#regex_47KXx9dLqeO8MNJeizLKhP’?
Use -v to see a list of the files searched for.
Text/Regex/TDFA/CorePattern.hs:37:8:
Could not find module ‘Control.Monad.RWS’
Perhaps you haven't installed the profiling libraries for package ‘mtl-2.2.1#mtl_Aue4leSeVkpKLsfHIV51E8’?
Use -v to see a list of the files searched for.
Text/Regex/TDFA/ReadRegex.hs:13:8:
`Could not find module ‘Text.ParserCombinators.Parsec’`
Perhaps you haven't installed the profiling libraries for package ‘parsec-3.1.9#parse_EE5NO1mlYLh4J8mgDEshNv’?
Use -v to see a list of the files searched for.
Text/Regex/TDFA/String.hs:23:8:
Could not find module ‘Text.Regex.Base.RegexLike’`
Perhaps you haven't installed the profiling libraries for package ‘regex-base-0.93.2#regex_47KXx9dLqeO8MNJeizLKhP’?
Use -v to see a list of the files searched for.
Text/Regex/TDFA/TDFA.hs:10:8:`
Could not find module ‘Control.Monad.State’
Perhaps you haven't installed the profiling libraries for package ‘mtl-2.2.1#mtl_Aue4leSeVkpKLsfHIV51E8’?
Use -v to see a list of the files searched for.
Makefile:16: recipe for target 'build' failed
make: *** [build] Error 1
user#user-VirtualBox:~/regex-tdfa-master$
However, nothing worked. Hence, any help would be so appreciated...
Text/Regex/TDFA/NewDFA/Engine.hs:13:33: parse error on input ‘#’
On an initial note, this error points to a module of the regex-tdfa package, so you should have gotten it when building the package, rather than when building your test.hs, unless you were trying to build test.hs after putting it within the package source tree. In any case, line 13 of the mentioned file is:
import GHC.Prim(MutableByteArray#,RealWorld,Int#,sizeofMutableByteArray#,unsafeCoerce#)
The # names require the MagicHash GHC extension to be enabled. As there is no {-# LANGUAGE MagicHash #-} pragma at the beginning of the file, one should assume the extension is enabled through the .cabal file of the package, and that is indeed the case. That being so, your problem seems to be that you are attempting use the package modules straight from the source tree, without using an appropriate build tool such as Cabal. (Note that if you did successfully run cabal install regex-tdfa there should be no need of dealing with the source tree: ghc --make -o test test.hs should be enough.)
P.S.: There is an error in your test.hs. The last line should be...
if str =~ regex then putStrLn "matched" else putStrLn "no matches"
(I did manage to run it after this correction.)
It looks like you are compiling your program from within Regex-TDFA source code. I am able to reproduce your problem if I do cabal unpack regex-tdfa && cd regex-tdfa-1.2.2 && ghc --make test.hs.
The error happens because when GHC finds Regex-TDFA source files in the current directory, it just picks them and tries to compile, as if they were ordinary source files belonging to your project. However, Regex-TDFA cannot be built with simple ghc --make: in order to build it, you have to run cabal first. Cabal will read regex-tdfa.cabal file that contains the list of the necessary GHC extensions.
In particular, parse error happens because GHC extension MagicHash is missing (that's where the hash # comes from).
The "fix" is to move your test.hs to some other location: then GHC will use system package for Regex-TDFA.
I have installed GHC through Nix:
$ nix-env -i ghc
Then I have installed the aeson package:
$ nix-env -f "<nixpkgs>" -iA haskellPackages.aeson
And pointed GHC to the Nix package folder:
$ export GHC_PACKAGE_PATH=~/.nix-profile/lib/ghc-8.0.1/package.conf.d/
Which seems to work:
$ ghc-pkg list
/Users/zoul/.nix-profile/lib/ghc-8.0.1/package.conf.d
Cabal-1.24.0.0
array-0.5.1.1
…
But the aeson package is missing from the list of packages above and can’t be loaded. Even though there’s clearly something there:
$ ls /Users/zoul/.nix-profile/lib/ghc-8.0.1/ | grep ^ae
aeson-0.11.2.1
What am I doing wrong?
You cannot install Haskell libraries in Nix that way because the ghc compiler you're using does not search your user's profile for libraries. Consequently, installing a library there has no effect. This topic is explained in great detail in the Nixpkgs user manual. I'm citing the relevant bit from "8.5.2.2. How to install a compiler with libraries":
GHC expects to find all installed libraries inside of its own lib directory. This approach works fine on traditional Unix systems, but it doesn’t work for Nix, because GHC’s store path is immutable once it’s built. We cannot install additional libraries into that location. As a consequence, our copies of GHC don’t know any packages except their own core libraries, like base, containers, Cabal, etc.
We can register additional libraries to GHC, however, using a special build function called ghcWithPackages. That function expects one argument: a function that maps from an attribute set of Haskell packages to a list of packages, which determines the libraries known to that particular version of GHC. For example, the Nix expression ghcWithPackages (pkgs: [pkgs.mtl]) generates a copy of GHC that has the mtl library registered in addition to its normal core packages:
$ nix-shell -p "haskellPackages.ghcWithPackages (pkgs: [pkgs.mtl])"
[nix-shell:~]$ ghc-pkg list mtl
/nix/store/zy79...-ghc-7.10.2/lib/ghc-7.10.2/package.conf.d:
mtl-2.2.1
This function allows users to define their own development environment by means of an override. After adding the following snippet to ~/.nixpkgs/config.nix,
{
packageOverrides = super: let self = super.pkgs; in
{
myHaskellEnv = self.haskell.packages.ghc7102.ghcWithPackages
(haskellPackages: with haskellPackages; [
# libraries
arrows async cgi criterion
# tools
cabal-install haskintex
]);
};
}
it’s possible to install that compiler with nix-env -f "<nixpkgs>" -iA myHaskellEnv.
While evaluating the line "import Control.Monad.State" in a Haskell module, GHC gives me the following error:
Could not find module `Control.Monad.State':
it was found in multiple packages: monads-fd-0.0.0.1 mtl-1.1.0.2
Failed, modules loaded: none.
How do I resolve this conflict?
You have several options. Either:
ghc-pkg hide monads-fd. This will cause GHC and GHCi to ignore the presence of the monads-fd by default until you later ghc-pkg expose monads-fd, but software installed by Cabal will still be able to build against it.
Use the {-# LANGUAGE PackageImports #-} pragma, and change your import statement to import "mtl" Control.Monad.State.
Use Cabal to build your project, and specify mtl in the Build-depends line.
The first is best for casual hacking, and the last is best for production builds.
These all assume you want the mtl module and not the monads-fd module; otherwise swap them.
Both packages implement Control.Monad.State and GHC does not know which implementation it should prefer, so you need to hide one of the packages from GHC. Seems like the -ignore-package <name> GHC flag might help you here.