Chapter 1. Introduction
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# Chapter 1. Introduction

This is Haddock, a tool for automatically generating documentation from annotated Haskell source code. Haddock was designed with several goals in mind:

- When documenting APIs, it is desirable to keep the documentation close to the actual interface or implementation of the API, preferably in the same file, to reduce the risk that the two become out of sync. Haddock therefore lets you write the documentation for an entity (function, type, or class) next to the definition of the entity in the source code.

- There is a tremendous amount of useful API documentation that can be extracted from just the bare source code, including types of exported functions, definitions of data types and classes, and so on. Haddock can therefore generate documentation from a set of straight Haskell 98 modules, and the documentation will contain precisely the interface that is available to a programmer using those modules.

- Documentation annotations in the source code should be easy on the eye when editing the source code itself, so as not to obscure the code and to make reading and writing documentation annotations easy. The easier it is to write documentation, the more likely the programmer is to do it. Haddock therefore uses lightweight markup in its annotations, taking several ideas from IDoc. In fact, Haddock can understand IDoc-annotated source code.

- The documentation should not expose any of the structure of the implementation, or to put it another way, the implementer of the API should be free to structure the implementation however he or she wishes, without exposing any of that structure to the consumer. In practical terms, this means that while an API may internally consist of several Haskell modules, we often only want to expose a single module to the user of the interface, where this single module just re-exports the relevant parts of the implementation modules.

  Haddock therefore understands the Haskell module system and can generate documentation which hides not only non-exported entities from the interface, but also the internal module structure of the interface. A documentation annotation can still be placed next to the implementation, and it will be propagated to the external module in the generated documentation.

- Being able to move around the documentation by following hyperlinks is essential. Documentation generated by Haddock is therefore littered with hyperlinks: every type and class name is a link to the corresponding definition, and user-written documentation annotations can contain identifiers which are linked automatically when the documentation is generated.

- We might want documentation in multiple formats - online and printed, for example. Haddock comes with HTML, LaTeX, and Hoogle backends, and it is structured in such a way that adding new backends is straightforward.

## 1.1. Obtaining Haddock

Distributions (source & binary) of Haddock can be obtained from its web site.

Up-to-date sources can also be obtained from our public darcs repository. The Haddock sources are at `http://code.haskell.org/haddock`. See darcs.net for more information on the darcs version control utility.

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