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Keywords: Functional programming, Haskell
Title: Programming In Haskell
Author: Graham Hutton
Publisher: Cambridge University Press
Verdict: Slightly academic but an interesting intro to Haskell all the same
While it may appear that to all intents and purposes object oriented programming has achieved dominance in terms of programming language paradigms, there still exist outposts that refuse to submit to the benefits of polymorphism, encapsulation and object inheritance. It's not just that there is a hard-core sticking to procedural coding in C and refusing to go the Java/C#/Python/Ruby route. There are also those who have taken the functional programming route to programming nirvana, particularly those who use the purist functional language of Haskell. And, surprising though it may seem to some, it's a topic that seems to be of increasing interest to the broader development community as well.
Despite the conceptual differences between object oriented and pure procedural languages they do in fact share common roots and a number of key features in common. Chief amongst these is that programs manipulate data and state. Computer scientists characterise this style of programming as imperative programming - the developer writes a series of statements that tell the computer what to do, changing the state of variables in order to complete whatever task the program is performing.
In contrast functional programming (FP) has no concept of state - there are no variables that the developer manipulates. Instead there are a series of functions which are applied to data and evaluated. Some of the data that these functions are applied to are themselves functions, and may deliver other functions as results. On the face of it this might seem like a bizarre and alien concept, and indeed the first time that one comes across Haskell or other functional programming language it does seem odd.
There is obviously a strongly mathematical flavour to Haskell, which this slim introductory volume does nothing to dispel. The academic tone is partly because the book is geared to the computer science student (complete with excercises at the end of each chapter), but it's also recognition of the roots of Haskell in the academic community.
The book opens with some introductory background and then moves on very quickly to syntax and program structure. The explanations are generally clear, and the text is illustrated with simple examples. The author has assumed no prior programming experience, but those who've programmed before in a non-FP language would probably appreciate a bit more guidance on the differences between the FP and non-FP way of doing things.
The book looks at key concepts such as data typing, curried functions, folding, filters and so on. What becomes apparent is that the language is concise, elegant and extremely powerful. It leaves the developer having to reason about algorithms without having to worry too much about the plumbing. Those who've programmed with APL, for example, will find a fair degree of familiarity. Similarly those who've come across lambda functions in other languages, such as Python or Ruby, will find that Haskell presents a much purer expression of functional programming.
For the practicing developer looking to utilise Haskell in action, the emphasis here is more on giving the reader a solid conceptual grounding rather than in more concrete programming tasks. While there are some extended examples in the latter part of the book, it's still by no means a very practically-focused tutorial.
Whether it's closures in Java, functional programming in Python or Ruby, XSLT transformations or new ideas in parallel computation, functional programming is providing input to many different areas of development. This book is a good place to get your head around some of its ideas, even if you don't intend to add Haskell to your program language arsenal just right now.