Example: A package containing a simple library

The HUnit package contains a file HUnit.cabal containing:

name:           HUnit
version:        1.1.1
synopsis:       A unit testing framework for Haskell
homepage:       http://hunit.sourceforge.net/
category:       Testing
author:         Dean Herington
license:        BSD3
license-file:   LICENSE
cabal-version:  >= 1.10
build-type:     Simple

library
  build-depends:      base >= 2 && < 4
  exposed-modules:    Test.HUnit.Base, Test.HUnit.Lang,
                      Test.HUnit.Terminal, Test.HUnit.Text, Test.HUnit
  default-extensions: CPP

and the following Setup.hs:

import Distribution.Simple
main = defaultMain

Example: A package containing executable programs

name:           TestPackage
version:        0.0
synopsis:       Small package with two programs
author:         Angela Author
license:        BSD3
build-type:     Simple
cabal-version:  >= 1.2

executable program1
  build-depends:  HUnit
  main-is:        Main.hs
  hs-source-dirs: prog1

executable program2
  main-is:        Main.hs
  build-depends:  HUnit
  hs-source-dirs: prog2
  other-modules:  Utils

with Setup.hs the same as above.

Example: A package containing a library and executable programs

name:            TestPackage
version:         0.0
synopsis:        Package with library and two programs
license:         BSD3
author:          Angela Author
build-type:      Simple
cabal-version:   >= 1.2

library
  build-depends:   HUnit
  exposed-modules: A, B, C

executable program1
  main-is:         Main.hs
  hs-source-dirs:  prog1
  other-modules:   A, B

executable program2
  main-is:         Main.hs
  hs-source-dirs:  prog2
  other-modules:   A, C, Utils

with Setup.hs the same as above. Note that any library modules required (directly or indirectly) by an executable must be listed again.

The trivial setup script used in these examples uses the simple build infrastructure provided by the Cabal library (see Distribution.Simple). The simplicity lies in its interface rather that its implementation. It automatically handles preprocessing with standard preprocessors, and builds packages for all the Haskell implementations (except nhc98, for now).

The simple build infrastructure can also handle packages where building is governed by system-dependent parameters, if you specify a little more (see the section on system-dependent parameters). A few packages require more elaborate solutions.

Modules and preprocessors

Haskell module names listed in the exposed-modules and other-modules fields may correspond to Haskell source files, i.e. with names ending in “.hs” or “.lhs”, or to inputs for various Haskell preprocessors. The simple build infrastructure understands the extensions:

• .gc (greencard)
• .chs (c2hs)
• .hsc (hsc2hs)
• .y and .ly (happy)
• .x (alex)
• .cpphs (cpphs)

When building, Cabal will automatically run the appropriate preprocessor and compile the Haskell module it produces.

Some fields take lists of values, which are optionally separated by commas, except for the build-depends field, where the commas are mandatory.

Some fields are marked as required. All others are optional, and unless otherwise specified have empty default values.

Package properties

These fields may occur in the first top-level properties section and describe the package as a whole:

name: package-name (required)

The unique name of the package, without the version number.

version: numbers (required)

The package version number, usually consisting of a sequence of natural numbers separated by dots.

cabal-version: >= x.y

The version of the Cabal specification that this package description uses. The Cabal specification does slowly evolve, intoducing new features and occasionally changing the meaning of existing features. By specifying which version of the spec you are using it enables programs which process the package description to know what syntax to expect and what each part means.

For historical reasons this is always expressed using >= version range syntax. No other kinds of version range make sense, in particular upper bounds do not make sense. In future this field will specify just a version number, rather than a version range.

The version number you specify will affect both compatability and behaviour. Most tools (including the Cabal libray and cabal program) understand a range of versions of the Cabal specification. Older tools will of course only work with older versions of the Cabal specification. Most of the time, tools that are too old will recognise this fact and produce a suitable error message.

As for behaviour, new versions of the Cabal spec can change the meaning of existing syntax. This means if you want to take advantage of the new meaning or behaviour then you must specify the newer Cabal version. Tools are expected to use the meaning and behaviour appropriate to the version given in the package description.

In particular, the syntax of package descriptions changed significantly with Cabal version 1.2 and the cabal-version field is now required. Files written in the old syntax are still recognized, so if you require compatability with very old Cabal versions then you may write your package description file using the old syntax. Please consult the user’s guide of an older Cabal version for a description of that syntax.

build-type: identifier

The type of build used by this package. Build types are the constructors of the BuildType type, defaulting to Custom. If this field is given a value other than Custom, some tools such as cabal-install will be able to build the package without using the setup script. So if you are just using the default Setup.hs then set the build type as Simple.

license: identifier (default: AllRightsReserved)

The type of license under which this package is distributed. License names are the constants of the License type.

license-file: filename

The name of a file containing the precise license for this package. It will be installed with the package.

copyright: freeform

The content of a copyright notice, typically the name of the holder of the copyright on the package and the year(s) from which copyright is claimed. For example: Copyright: (c) 2006-2007 Joe Bloggs

author: freeform

The original author of the package.

Remember that .cabal files are Unicode, using the UTF–8 encoding.

maintainer: address

The current maintainer or maintainers of the package. This is an e-mail address to which users should send bug reports, feature requests and patches.

stability: freeform

The stability level of the package, e.g. alpha, experimental, provisional, stable.

homepage: URL

The package homepage.

bug-reports: URL

The URL where users should direct bug reports. This would normally be either:

• A mailto: URL, eg for a person or a mailing list.

• An http: (or https:) URL for an online bug tracking system.

For example Cabal itself uses a web-based bug tracking system

bug-reports: http://hackage.haskell.org/trac/hackage/

package-url: URL

The location of a source bundle for the package. The distribution should be a Cabal package.

synopsis: freeform

A very short description of the package, for use in a table of packages. This is your headline, so keep it short (one line) but as informative as possible. Save space by not including the package name or saying it’s written in Haskell.

description: freeform

Description of the package. This may be several paragraphs, and should be aimed at a Haskell programmer who has never heard of your package before.

For library packages, this field is used as prologue text by setup haddock, and thus may contain the same markup as haddock documentation comments.

category: freeform

A classification category for future use by the package catalogue Hackage. These categories have not yet been specified, but the upper levels of the module hierarchy make a good start.

tested-with: compiler list

A list of compilers and versions against which the package has been tested (or at least built).

data-files: filename list

A list of files to be installed for run-time use by the package. This is useful for packages that use a large amount of static data, such as tables of values or code templates. Cabal provides a way to find these files at run-time.

A limited form of * wildcards in file names, for example data-files: images/*.png matches all the .png files in the images directory.

The limitation is that * wildcards are only allowed in place of the file name, not in the directory name or file extension. In particular, wildcards do not include directories contents recursively. Furthermore, if a wildcard is used it must be used with an extension, so data-files: data/* is not allowed. When matching a wildcard plus extension, a file’s full extension must match exactly, so *.gz matches foo.gz but not foo.tar.gz. A wildcard that does not match any files is an error.

The reason for providing only a very limited form of wildcard is to concisely express the common case of a large number of related files of the same file type without making it too easy to accidentally include unwanted files.

data-dir: directory

The directory where Cabal looks for data files to install, relative to the source directory. By default, Cabal will look in the source directory itself.

extra-source-files: filename list

A list of additional files to be included in source distributions built with setup sdist. As with data-files it can use a limited form of * wildcards in file names.

extra-tmp-files: filename list

A list of additional files or directories to be removed by setup clean. These would typically be additional files created by additional hooks, such as the scheme described in the section on system-dependent parameters.

Library

The library section should contain the following fields:

exposed-modules: identifier list (required if this package contains a library)

A list of modules added by this package.

exposed: boolean (default: True)

Some Haskell compilers (notably GHC) support the notion of packages being “exposed” or “hidden” which means the modules they provide can be easily imported without always having to specify which package they come from. However this only works effectively if the modules provided by all exposed packages do not overlap (otherwise a module import would be ambiguous).

Almost all new libraries use hierarchical module names that do not clash, so it is very uncommon to have to use this field. However it may be necessary to set exposed: False for some old libraries that use a flat module namespace or where it is known that the exposed modules would clash with other common modules.

The library section may also contain build information fields (see the section on build information).

Executables

Executable sections (if present) describe executable programs contained in the package and must have an argument after the section label, which defines the name of the executable. This is a freeform argument but may not contain spaces.

The executable may be described using the following fields, as well as build information fields (see the section on build information).

main-is: filename (required)

The name of the .hs or .lhs file containing the Main module. Note that it is the .hs filename that must be listed, even if that file is generated using a preprocessor. The source file must be relative to one of the directories listed in hs-source-dirs.

Test suites

Test suite sections (if present) describe package test suites and must have an argument after the section label, which defines the name of the test suite. This is a freeform argument, but may not contain spaces. It should be unique among the names of the package’s other test suites, the package’s executables, and the package itself. Using test suite sections requires at least Cabal version 1.9.2.

The test suite may be described using the following fields, as well as build information fields (see the section on build information).

type: interface (required)

The interface type and version of the test suite. Cabal supports two test suite interfaces, called exitcode-stdio-1.0 and detailed-1.0. Each of these types may require or disallow other fields as described below.

Test suites using the exitcode-stdio-1.0 interface are executables that indicate test failure with a non-zero exit code when run; they may provide human-readable log information through the standard output and error channels. This interface is provided primarily for compatibility with existing test suites; it is preferred that new test suites be written for the detailed-1.0 interface. The exitcode-stdio-1.0 type requires the main-is field.

main-is: filename (required: exitcode-stdio-1.0, disallowed: detailed-1.0)

The name of the .hs or .lhs file containing the Main module. Note that it is the .hs filename that must be listed, even if that file is generated using a preprocessor. The source file must be relative to one of the directories listed in hs-source-dirs. This field is analogous to the main-is field of an executable section.

Test suites using the detailed-1.0 interface are modules exporting the symbol tests :: [Test]. The Test type is exported by the module Distribution.TestSuite provided by Cabal. For more details, see the example below.

The detailed-1.0 interface allows Cabal and other test agents to inspect a test suite’s results case by case, producing detailed human- and machine-readable log files. The detailed-1.0 interface requires the test-module field.

test-module: identifier (required: detailed-1.0, disallowed: exitcode-stdio-1.0)

The module exporting the tests symbol.

Name:           foo
Version:        1.0
License:        BSD3
Cabal-Version:  >= 1.9.2
Build-Type:     Simple

Test-Suite test-foo
    type:       exitcode-stdio-1.0
    main-is:    test-foo.hs
    build-depends: base

module Main where

import System.Exit (exitFailure)

main = do
    putStrLn "This test always fails!"
    exitFailure

Name:           bar
Version:        1.0
License:        BSD3
Cabal-Version:  >= 1.9.2
Build-Type:     Simple

Test-Suite test-bar
    type:       detailed-1.0
    test-module: Test.Bar
    build-depends: base, Cabal >= 1.9.2

{-# LANGUAGE FlexibleInstances #-}
module Test.Bar ( tests ) where

import Distribution.TestSuite

instance TestOptions (String, Bool) where
    name = fst
    options = const []
    defaultOptions _ = return (Options [])
    check _ _ = []

instance PureTestable (String, Bool) where
    run (name, result) _ | result == True = Pass
                         | result == False = Fail (name ++ " failed!")

test :: (String, Bool) -> Test
test = pure

-- In actual usage, the instances 'TestOptions (String, Bool)' and
-- 'PureTestable (String, Bool)', as well as the function 'test', would be
-- provided by the test framework.

tests :: [Test]
tests =
    [ test ("bar-1", True)
    , test ("bar-2", False)
    ]

$ cabal configure --enable-tests
$ cabal build
$ cabal test

Benchmarks

Benchmark sections (if present) describe benchmarks contained in the package and must have an argument after the section label, which defines the name of the benchmark. This is a freeform argument, but may not contain spaces. It should be unique among the names of the package’s other benchmarks, the package’s test suites, the package’s executables, and the package itself. Using benchmark sections requires at least Cabal version 1.9.2.

The benchmark may be described using the following fields, as well as build information fields (see the section on build information).

type: interface (required)

The interface type and version of the benchmark. At the moment Cabal only support one benchmark interface, called exitcode-stdio-1.0.

Benchmarks using the exitcode-stdio-1.0 interface are executables that indicate failure to run the benchmark with a non-zero exit code when run; they may provide human-readable information through the standard output and error channels.

main-is: filename (required: exitcode-stdio-1.0)

The name of the .hs or .lhs file containing the Main module. Note that it is the .hs filename that must be listed, even if that file is generated using a preprocessor. The source file must be relative to one of the directories listed in hs-source-dirs. This field is analogous to the main-is field of an executable section.

Name:           foo
Version:        1.0
License:        BSD3
Cabal-Version:  >= 1.9.2
Build-Type:     Simple

Benchmark bench-foo
    type:       exitcode-stdio-1.0
    main-is:    bench-foo.hs
    build-depends: base, time

{-# LANGUAGE BangPatterns #-}
module Main where

import Data.Time.Clock

fib 0 = 1
fib 1 = 1
fib n = fib (n-1) + fib (n-2)

main = do
    start <- getCurrentTime
    let !r = fib 20
    end <- getCurrentTime
    putStrLn $ "fib 20 took " ++ show (diffUTCTime end start)

$ cabal configure --enable-benchmarks
$ cabal build
$ cabal bench

Build information

The following fields may be optionally present in a library or executable section, and give information for the building of the corresponding library or executable. See also the sections on system-dependent parameters and configurations for a way to supply system-dependent values for these fields.

build-depends: package list

A list of packages needed to build this one. Each package can be annotated with a version constraint.

Version constraints use the operators ==, >=, >, <, <= and a version number. Multiple constraints can be combined using && or ||. If no version constraint is specified, any version is assumed to be acceptable. For example:

library
  build-depends:
    base >= 2,
    foo >= 1.2 && < 1.3,
    bar

Dependencies like foo >= 1.2 && < 1.3 turn out to be very common because it is recommended practise for package versions to correspond to API versions. As of Cabal 1.6, there is a special syntax to support this use:

build-depends: foo ==1.2.*

It is only syntactic sugar. It is exactly equivalent to foo >= 1.2 && < 1.3.

Note: Prior to Cabal 1.8, build-depends specified in each section were global to all sections. This was unintentional, but some packages were written to depend on it, so if you need your build-depends to be local to each section, you must specify at least Cabal-Version: >= 1.8 in your .cabal file.

other-modules: identifier list

A list of modules used by the component but not exposed to users. For a library component, these would be hidden modules of the library. For an executable, these would be auxiliary modules to be linked with the file named in the main-is field.

Note: Every module in the package must be listed in one of other-modules, exposed-modules or main-is fields.

hs-source-dirs: directory list (default: “.”)

Root directories for the module hierarchy.

For backwards compatibility, the old variant hs-source-dir is also recognized.

extensions: identifier list

A list of Haskell extensions used by every module. Extension names are the constructors of the Extension type. These determine corresponding compiler options. In particular, CPP specifies that Haskell source files are to be preprocessed with a C preprocessor.

Extensions used only by one module may be specified by placing a LANGUAGE pragma in the source file affected, e.g.:

{-# LANGUAGE CPP, MultiParamTypeClasses #-}

Note: GHC versions prior to 6.6 do not support the LANGUAGE pragma.

build-tools: program list

A list of programs, possibly annotated with versions, needed to build this package, e.g. c2hs >= 0.15, cpphs.If no version constraint is specified, any version is assumed to be acceptable.

buildable: boolean (default: True)

Is the component buildable? Like some of the other fields below, this field is more useful with the slightly more elaborate form of the simple build infrastructure described in the section on system-dependent parameters.

ghc-options: token list

Additional options for GHC. You can often achieve the same effect using the extensions field, which is preferred.

Options required only by one module may be specified by placing an OPTIONS_GHC pragma in the source file affected.

ghc-prof-options: token list

Additional options for GHC when the package is built with profiling enabled.

ghc-shared-options: token list

Additional options for GHC when the package is built as shared library.

hugs-options: token list

Additional options for Hugs. You can often achieve the same effect using the extensions field, which is preferred.

Options required only by one module may be specified by placing an OPTIONS_HUGS pragma in the source file affected.

nhc98-options: token list

Additional options for nhc98. You can often achieve the same effect using the extensions field, which is preferred.

Options required only by one module may be specified by placing an OPTIONS_NHC98 pragma in the source file affected.

includes: filename list

A list of header files to be included in any compilations via C. This field applies to both header files that are already installed on the system and to those coming with the package to be installed. These files typically contain function prototypes for foreign imports used by the package.

install-includes: filename list

A list of header files from this package to be installed into $libdir/includes when the package is installed. Files listed in install-includes: should be found in relative to the top of the source tree or relative to one of the directories listed in include-dirs.

install-includes is typically used to name header files that contain prototypes for foreign imports used in Haskell code in this package, for which the C implementations are also provided with the package. Note that to include them when compiling the package itself, they need to be listed in the includes: field as well.

include-dirs: directory list

A list of directories to search for header files, when preprocessing with c2hs, hsc2hs, ffihugs, cpphs or the C preprocessor, and also when compiling via C.

c-sources: filename list

A list of C source files to be compiled and linked with the Haskell files.

If you use this field, you should also name the C files in CFILES pragmas in the Haskell source files that use them, e.g.: {-# CFILES dir/file1.c dir/file2.c #-} These are ignored by the compilers, but needed by Hugs.

extra-libraries: token list

A list of extra libraries to link with.

extra-lib-dirs: directory list

A list of directories to search for libraries.

cc-options: token list

Command-line arguments to be passed to the C compiler. Since the arguments are compiler-dependent, this field is more useful with the setup described in the section on system-dependent parameters.

ld-options: token list

Command-line arguments to be passed to the linker. Since the arguments are compiler-dependent, this field is more useful with the setup described in the section on system-dependent parameters>.

pkgconfig-depends: package list

A list of pkg-config packages, needed to build this package. They can be annotated with versions, e.g. gtk+-2.0 >= 2.10, cairo >= 1.0. If no version constraint is specified, any version is assumed to be acceptable. Cabal uses pkg-config to find if the packages are available on the system and to find the extra compilation and linker options needed to use the packages.

If you need to bind to a C library that supports pkg-config (use pkg-config --list-all to find out if it is supported) then it is much preferable to use this field rather than hard code options into the other fields.

frameworks: token list

On Darwin/MacOS X, a list of frameworks to link to. See Apple’s developer documentation for more details on frameworks. This entry is ignored on all other platforms.

Configurations

Library and executable sections may include conditional blocks, which test for various system parameters and configuration flags. The flags mechanism is rather generic, but most of the time a flag represents certain feature, that can be switched on or off by the package user. Here is an example package description file using configurations:

Name: Test1
Version: 0.0.1
Cabal-Version: >= 1.2
License: BSD3
Author:  Jane Doe
Synopsis: Test package to test configurations
Category: Example

Flag Debug
  Description: Enable debug support
  Default:     False

Flag WebFrontend
  Description: Include API for web frontend.
  -- Cabal checks if the configuration is possible, first
  -- with this flag set to True and if not it tries with False

Library
  Build-Depends:   base
  Exposed-Modules: Testing.Test1
  Extensions:      CPP

  if flag(debug)
    GHC-Options: -DDEBUG
    if !os(windows)
      CC-Options: "-DDEBUG"
    else
      CC-Options: "-DNDEBUG"

  if flag(webfrontend)
    Build-Depends: cgi > 0.42
    Other-Modules: Testing.WebStuff

Executable test1
  Main-is: T1.hs
  Other-Modules: Testing.Test1
  Build-Depends: base

  if flag(debug)
    CC-Options: "-DDEBUG"
    GHC-Options: -DDEBUG

Name: Test1
Version: 0.0.1
Cabal-Version: >= 1.2
License: BSD3
Author:  Jane Doe
Synopsis: Test package to test configurations
Category: Example

Flag Debug {
  Description: Enable debug support
  Default:     False
}

Library {
  Build-Depends:   base
  Exposed-Modules: Testing.Test1
  Extensions:      CPP
  if flag(debug) {
    GHC-Options: -DDEBUG
    if !os(windows) {
      CC-Options: "-DDEBUG"
    } else {
      CC-Options: "-DNDEBUG"
    }
  }
}

  `if `_condition_
       _property-descriptions-or-conditionals*_

  `if `_condition_
       _property-descriptions-or-conditionals*_
  `else`
       _property-descriptions-or-conditionals*_

Meaning of field values when using conditionals

During the configuration phase, a flag assignment is chosen, all conditionals are evaluated, and the package description is combined into a flat package descriptions. If the same field both inside a conditional and outside then they are combined using the following rules.

• Boolean fields are combined using conjunction (logical “and”).

• List fields are combined by appending the inner items to the outer items, for example

  Extensions: CPP
  if impl(ghc) || impl(hugs)
    Extensions: MultiParamTypeClasses
  

  when compiled using Hugs or GHC will be combined to

  Extensions: CPP, MultiParamTypeClasses
  

  Similarly, if two conditional sections appear at the same nesting level, properties specified in the latter will come after properties specified in the former.

• All other fields must not be specified in ambiguous ways. For example

  Main-is: Main.hs
  if flag(useothermain)
    Main-is: OtherMain.hs
  

  will lead to an error. Instead use

  if flag(useothermain)
    Main-is: OtherMain.hs
  else
    Main-is: Main.hs
  

Source Repositories

It is often useful to be able to specify a source revision control repository for a package. Cabal lets you specifying this information in a relatively structured form which enables other tools to interpret and make effective use of the information. For example the information should be sufficient for an automatic tool to checkout the sources.

Cabal supports specifying different information for various common source control systems. Obviously not all automated tools will support all source control systems.

Cabal supports specifying repositories for different use cases. By declaring which case we mean automated tools can be more useful. There are currently two kinds defined:

• The head kind refers to the latest development branch of the package. This may be used for example to track activity of a project or as an indication to outside developers what sources to get for making new contributions.

• The this kind refers to the branch and tag of a repository that contains the sources for this version or release of a package. For most source control systems this involves specifying a tag, id or hash of some form and perhaps a branch. The purpose is to be able to reconstruct the sources corresponding to a particular package version. This might be used to indicate what sources to get if someone needs to fix a bug in an older branch that is no longer an active head branch.

You can specify one kind or the other or both. As an example here are the repositories for the Cabal library. Note that the this kind of repo specifies a tag.

source-repository head
  type:     darcs
  location: http://darcs.haskell.org/cabal/

source-repository this
  type:     darcs
  location: http://darcs.haskell.org/cabal-branches/cabal-1.6/
  tag:      1.6.1

The exact fields are as follows:

type: token

The name of the source control system used for this repository. The currently recognised types are:

• darcs
• git
• svn
• cvs
• mercurial (or alias hg)
• bazaar (or alias bzr)
• arch
• monotone

This field is required.

location: URL

The location of the repository. The exact form of this field depends on the repository type. For example:

• for darcs: http://code.haskell.org/foo/
• for git: git://github.com/foo/bar.git
• for CVS: anoncvs@cvs.foo.org:/cvs

This field is required.

module: token

CVS requires a named module, as each CVS server can host multiple named repositories.

This field is required for the CVS repo type and should not be used otherwise.

branch: token

Many source control systems support the notion of a branch, as a distinct concept from having repositories in separate locations. For example CVS, SVN and git use branches while for darcs uses different locations for different branches. If you need to specify a branch to identify a your repository then specify it in this field.

This field is optional.

tag: token

A tag identifies a particular state of a source repository. The tag can be used with a this repo kind to identify the state of a repo corresponding to a particular package version or release. The exact form of the tag depends on the repository type.

This field is required for the this repo kind.

subdir: directory

Some projects put the sources for multiple packages under a single source repository. This field lets you specify the relative path from the root of the repository to the top directory for the package, ie the directory containing the package’s .cabal file.

This field is optional. It default to empty which corresponds to the root directory of the repository.

Accessing the package version

The aforementioned auto generated Paths_pkgname module also exports the constant version :: Version which is defined as the version of your package as specified in the version field.

Example: Using autoconf

This example is for people familiar with the autoconf tools.

In the X11 package, the file configure.ac contains:

AC_INIT([Haskell X11 package], [1.1], [libraries@haskell.org], [X11])

# Safety check: Ensure that we are in the correct source directory.
AC_CONFIG_SRCDIR([X11.cabal])

# Header file to place defines in
AC_CONFIG_HEADERS([include/HsX11Config.h])

# Check for X11 include paths and libraries
AC_PATH_XTRA
AC_TRY_CPP([#include <X11/Xlib.h>],,[no_x=yes])

# Build the package if we found X11 stuff
if test "$no_x" = yes
then BUILD_PACKAGE_BOOL=False
else BUILD_PACKAGE_BOOL=True
fi
AC_SUBST([BUILD_PACKAGE_BOOL])

AC_CONFIG_FILES([X11.buildinfo])
AC_OUTPUT

Then the setup script will run the configure script, which checks for the presence of the X11 libraries and substitutes for variables in the file X11.buildinfo.in:

buildable: @BUILD_PACKAGE_BOOL@
cc-options: @X_CFLAGS@
ld-options: @X_LIBS@

This generates a file X11.buildinfo supplying the parameters needed by later stages:

buildable: True
cc-options:  -I/usr/X11R6/include
ld-options:  -L/usr/X11R6/lib

The configure script also generates a header file include/HsX11Config.h containing C preprocessor defines recording the results of various tests. This file may be included by C source files and preprocessed Haskell source files in the package.

Note: Packages using these features will also need to list additional files such as configure, templates for .buildinfo files, files named only in .buildinfo files, header files and so on in the extra-source-files field, to ensure that they are included in source distributions. They should also list files and directories generated by configure in the extra-tmp-files field to ensure that they are removed by setup clean.