Haskell



Haskell is a functional programming language. It is distinct in a few ways:


 * Haskell is pure. A function when invoked using the same arguments will return the same result every time.
 * Haskell is lazy. Evaluations are performed only when needed.
 * Haskell provides a modern type system with state-of-the-art features like type classes and generalized algebraic data types (soon enough, terms like those will roll smoothly off your tongue).

Haskell is enjoyable to use because dealing with pure functions makes code much easier to reason about, and the advanced type system helps catch silly and profound mistakes.

Our aim in this book is to introduce you to the Haskell programming language &mdash; from the very basics to advanced features &mdash; and to computer programming in general. We urge seasoned programmers to be especially patient with this process. The languages you are familiar with are likely to differ greatly from Haskell, and the habits acquired from those languages might make it difficult to understand how things work &mdash; Haskell is simple, but different. Learning to see the world through the warped mindset of a functional programmer is an adventure in a brave new world, which brings knowledge valuable far beyond the boundaries of any language.

Overview
The book is divided into three sections: a Beginner's Track, an Advanced Track, and a section called Haskell in Practice. The last section, which covers practical use cases, depends only on the Beginner's Track. Seasoned programmers may read the overview to quickly evaluate what makes Haskell unique and different from other languages.

Beginner's Track
This section introduces you to Haskell basics and some commonly used libraries. At the end of this track, you should be able to write simple Haskell programs. Most chapters include exercises, with solutions, for your practice.

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Haskell Basics
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Elementary Haskell
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Intermediate Haskell
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Monads

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Advanced Track
This section introduces wider functional programming concepts such as different data structures and type theory. It will also cover more practical topics like concurrency.

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Welcome to Haskell
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Fun with Types
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Wider Theory
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Haskell Performance

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Haskell in Practice
Day-to-day issues of working with Haskell include items such as knowing the standard libraries, building graphical interfaces, and working with databases. You should be able to jump directly to this section from the beginner's track.

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Libraries Reference
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General Practices
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Specialised Tasks

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Appendices

 * /Syntactic sugar/
 * Answers to exercises
 * Authors and Acknowledgements

About the book

 * /Notes for contributors/
 * /Style conventions/
 * /To do/
 * Templates for the Haskell wikibook
 * Experimental Modules
 * List of topics

Other Haskell tutorials

 * Haskell Meta-tutorial &mdash; the tutorial to find other tutorials
 * Learn You a Haskell for Great Good &mdash; Tutorial aimed at beginners who may have experience in imperative programming languages but haven't programmed in a functional language before. Available online at no charge (CC BY-NC-SA license); also released as a conventional book.
 * Real World Haskell &mdash; an O'Reilly book, available online at no charge (CC BY-NC license). Built around case studies of practical applications.

Tutorials that have been incorporated into the Haskell Wikibook
The following may be read independently, but their content has been imported and adapted already into the Wikibook here


 * Write Yourself a Scheme in 48 Hours &mdash; An alternate approach to teaching Haskell (and perhaps Scheme), aimed at a more advanced audience (though not necessarily one that knows how to program!)
 * Yet Another Haskell Tutorial &mdash; aimed at beginners and takes a practical approach to things.

Additional resources

 * Learning Haskell at haskell.org
 * What I Wish I Knew When Learning Haskell — A wide-ranging collection of concise summaries of many intermediate and advanced Haskell topics. Released in the public domain.

Funktionale Programmierung mit Haskell Haskell Programmation Haskell Haskell Haskell Haskell HaskellWikiBook Haskell