Basics

Overview

We gave a simplified definition of a package in the last section. In this section, we will expand on the definition and provide different examples of a package.

Terminology

A package is a group of components, each of which is individually configured with their own sets of source files, compiler flags, and so on.

There are three types of components:

• library
• executable
• test

A single package can contain at most one library and any number of executables and tests.

A stanza is a block in the .cabal file that delimits a component. All the configuration for a component must be indented underneath the stanza declaration.

Library

A library component is configured by a library stanza. A library component must have an exposed-modules field which denotes the public API of the library. The other-modules field corresponds to modules which are internal and cannot be imported by the dependent packages.

Executable

An executable component is configured by an executable stanza. It must have a main-is field which specifies the name of the file relative to the specified hs-source-dirs field that contains the main function, the entry point to an Eta program. The modules that the component depends on must be specified in the other-modules field.

Example

The eta-first project in Initializing already shows an example.

Test

An test component is configured by an test stanza. It must have a main-is field which specifies the name of the file relative to the specified hs-source-dirs field that contains the main function, the entry point to an Eta program. The modules that the component depends on must be specified in the other-modules field.

A test component must also have a type field which currently only has one valid value: exitcode-stdio-1.0.

By default, the test components of a package are not built by default. You can use the --enable-tests flag when building to enable them, or put tests: True in your cabal.project file.

Next Section

In the next We will now move on to the section on build configuration.