A historical primer of F#

With the advent of a multi-paradigm language with functional programming support such as Lisp in 1958 by John McCarthy, the functional paradigm gained mainstream exposure. Due to its multi-paradigm nature, there is a debate around Lisp being a pure functional programming language. However, Scheme, one of the Lisp dialects which didn't appear till 1975, tends to favor the functional style. The salient features of this style includes use of tail recursion and continuations to express control flow.

Furthermore, various other functional languages were developed in academia, mostly in the areas of mathematical sciences for theorem proving. ML (meta-language) by Robin Milner et al of University of Edinburgh (early 1970s) is a prime example of a programming language used to first implement the Hindley–Milner type inference system. This simply typed polymorphic lambda calculus language was later adapted to build StandardML, Caml, and OCaml, unifying functional, OOP, and imperative programming paradigms. Haskell emerged in 1990 by Simon Jones et al as a purely functional programming language. Haskell supports lazy evaluation, non-strict semantics, and strong static typing. Haskell is named after the logician Haskell Curry. Not surprisingly, Currying is the functional approach to deconstructing a tuple into evaluating a sequence of functions. It allows us to deconstruct a function that takes multiple arguments into an equivalent sequence of sub-functions that are evaluated, one argument at a time. We will explore currying further in the book.

F#, a product of Don Syme, and Microsoft Research, surfaced in 2005 as a modern multi-paradigm functional programming language. F# originates from ML and has been influenced by OCaml, C#, Python, Haskell, Scala, and Erlang. F# Software Foundation (FSSF) defines the language as follows:

"F# is a mature, open source, cross-platform, functional-first programming language. It empowers users and organizations to tackle complex computing problems with simple, maintainable and robust code."

With an open source compiler, library, and toolset, F# is a multi-paradigm language for the .NET platform with support for multiple operating systems via Mono. It supports functional, object oriented, imperative, and explorative programming paradigms. Software developers who specialize in Microsoft platform and tools can easily learn to take advantage of this new language's functional and object-oriented features. This allows them to use their existing skills, find new productivity gains, and leverage new programming design approaches that cannot be easily expressed in objects alone.

We will be the first to admit that functional programming can be scary for those accustomed to the object oriented and imperative style of coding. While functional programming can lead to some mind-bending coding, the fundamentals are quite straightforward. If you find yourself lost in lambdas, rest assured that it takes everyone some time to master these expressions. Even though the primary focus of this book is not F# programming but rather data structures, we will start by introducing some of the F# language tenets to help get the reader up-to-speed.

The syntactical terseness of a functional language like F# can have an adverse effect on the reader; since functional programming is characterized by its concise coding style, brevity, and explicit modeling, this can be hard for those familiar with the verbose algorithmic style of OO and imperative languages. Rest assured, F# also offers a rich set of object oriented features and its integration with other .NET languages such as C#.NET and VB.NET is nearly seamless.