This tutorial assumes you’ve already installed the Stack build tool. If you haven’t yet, please start with the get started page and then come back here.
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In this article we’ll be talking about how to build full fledged projects consisting of libraries, executables, test suites, and benchmarks in Haskell with Stack.
You can start a new project with the command:
stack new my-project-name
This will use the default project template. You can also choose from many available templates which you can list with
For example, if you wanted to the
simple template instead, you could
stack new my-project-name simple
You should now have a directory named
my-project-name (or whatever
string you used), with a
stack.yaml file inside of it. A
stack.yaml file must be present in the root directory of each
project, and provides a number of settings. You can edit that file and
view the comments, or
view the configuration file documentation.
If you have an existing Cabal package, you can use the
command inside the package directory to initialize a
file. Stack will attempt to determine a package set compatible with
the packages requested in your
Note the difference in terminology above. This is important: a cabal
package is identified by a single
.cabal file, and has 0 or 1
libraries, and 0 or more executables, test suites, and benchmarks.
A Stack project has 1 or more cabal packages, and can build them all at the same time. In likely the majority of cases, your Stack project will have just one cabal package in it. However, multi-package projects can be very common for both open source library collections and for structuring commercial applications. Some open source examples of multi-package projects include Yesod, WAI, and Servant.
The basic command for building your project is
Very likely, you’ll need to first tell Stack to install the appropriate GHC version for your project. You can do this with:
or by using the
--install-ghc option to
stack --install-ghc build
Let’s suppose your project defines an executable called
my-executable. How do you run it? There are three common ways:
stack exec my-executablewill modify your
PATHvariable to include a number of additional directories, including the internal executable destination, and your build tools (like
stack exec which my-executablewill use the
whichcommand to find the full path to your executable, which you could then run, without the additional modifications that
stack execimplies. If you want to be clever, you could do something like this from your shell:
$ $(stack exec which my-executable)
stack installcommand will copy your executables into a user-specific directory, such as
$HOME/.local/binon POSIX systems. The directory will be printed to your console.
Testing is also straightforward:
As it happens, this is just a convenience shortcut for:
stack build --test
The same applies to
stack bench (for benchmarking) and
stack haddock (for building Haddock documentation). What this means is that
you can compose these flags to build the code, build the docs, run
tests, and run benchmarks:
stack build --test --bench --haddock
--file-watchwill run build in file-watch mode, where it will wait for changes to files and then automatically rebuild. This can be very convenient to run in a terminal while simulatenously editing in another window.
--fastwill disable optimizations
-Wall -Werrorfor GHC (all warnings on, and warnings treated as errors)
So throwing a few of these together:
stack build --test --file-watch --fast --pedantic
This is a small taste of the capabilities of Stack for building projects. You can find much more information in the Stack user guide.