Introduction in Font

Creator Data Matrix 2d barcode in Font Introduction

his introductory chapter will address some of the major questions you may have about F# and functional programming.

Functional programming (FP) is the oldest of the three major programming paradigms. The first FP language, IPL, was invented in 1955, about a year before Fortran. The second, Lisp, was invented in 1958, a year before Cobol. Both Fortran and Cobol are imperative (or procedural) languages, and their immediate success in scientific and business computing made imperative programming the dominant paradigm for more than 30 years. The rise of the object-oriented (OO) paradigm in the 1970s and the gradual maturing of OO languages ever since have made OO programming the most popular paradigm today. Despite the vigorous and continuous development of powerful FP languages (SML, OCaml, Haskell, and Clean, among others) and FP-like languages (APL and Lisp being the most successful for real-world applications) since the 1950s, FP remained a primarily academic pursuit until recently. The early commercial success of imperative languages made it the dominant paradigm for decades. Object-oriented languages gained broad acceptance only when enterprises recognized the need for more sophisticated computing solutions. Today, the promise of FP is finally being realized to solve even more complex problems as well as the simpler ones. Pure functional programming views all programs as collections of functions that accept arguments and return values. Unlike imperative and object-oriented programming, it allows no side effects and uses recursion instead of loops for iteration. The functions in a functional program are very much like mathematical functions because they do not change the state of the program. In the simplest terms, once a value is assigned to an identifier, it never changes, functions do not alter parameter values, and the results that functions return are completely new values. In typical underlying implementations, once a value is assigned to an area in memory, it does not change. To create results, functions copy values and then change the copies, leaving the original values free to be used by other functions and eventually be thrown away when no longer needed. (This is where the idea of garbage collection originated.) The mathematical basis for pure functional programming is elegant, and FP therefore provides beautiful, succinct solutions for many computing problems, but its stateless and recursive nature makes the other paradigms convenient for handling many common programming tasks. However, one of F# s great strengths is that you can use multiple paradigms and mix them to solve problems in the way you find most convenient.

When people think of functional programming, they often view its statelessness as a fatal flaw, without considering its advantages. One could argue that since an imperative program is often 90 percent assignment and since a functional program has no assignment, a functional program could be 90 percent shorter. However, not many people are convinced by such arguments or attracted to the ascetic world of stateless recursive programming, as John Hughes pointed out in his classic paper Why Functional Programming Matters : The functional programmer sounds rather like a medieval monk, denying himself the pleasures of life in the hope that it will make him virtuous. John Hughes, Chalmers University of Technology (http://www.math.chalmers.se/~rjmh/Papers/whyfp.html) To see the advantages of functional programming, you must look at what FP permits, rather than what it prohibits. For example, functional programming allows you to treat functions themselves as values and pass them to other functions. This might not seem all that important at first glance, but its implications are extraordinary. Eliminating the distinction between data and function means that many problems can be more naturally solved. Functional programs can be shorter and more modular than corresponding imperative and object-oriented programs. In addition to treating functions as values, functional languages offer other features that borrow from mathematics and are not commonly found in imperative languages. For example, functional programming languages often offer curried functions, where arguments can be passed to a function one at a time and, if all arguments are not given, the result is a residual function waiting for the rest of its parameters. It s also common for functional languages to offer type systems with much better power-to-weight ratios, providing more performance and correctness for less effort. Further, a function might return multiple values, and the calling function is free to consume them as it likes. I ll discuss these ideas, along with many more, in detail and with plenty of examples, in 3.

What Is F#

Functional programming is the best approach to solving many thorny computing problems, but pure FP isn t suitable for general-purpose programming. So, FP languages have gradually embraced aspects of the imperative and OO paradigms, remaining true to the FP paradigm but incorporating features needed to easily write any kind of program. F# is a natural successor on this path. It is also much more than just an FP language. Some of the most popular functional languages, including OCaml, Haskell, Lisp, and Scheme, have traditionally been implemented using custom runtimes, which leads to problems such as lack of interoperability. F# is a general-purpose programming language for .NET, a general-purpose runtime. F# smoothly integrates all three major programming paradigms. With F#, you can choose whichever paradigm works best to solve problems in the most effec, tive way. You can do pure FP if you re a purist, but you can easily combine functional,