I've had an obsession with programming languages for some time now. This probably began the first time I learned of LISP. Most people I know have had a similar "Ah-Hah!" moment associated with LISP, but it was when I first truly realized the deep extent to which a programming language shapes thought -- sometimes in negative ways. LISP put it all into perspective.

Since then, the obsession has only become worse through my employment at Microsoft, where I've had the privilege to work alongside and interact with some of the greatest minds in programming languages. This is an absolute honor. I worked on a few compilers and did some language design, particularly when on the Common Language Runtime team, and my favorite project today is my work on type-system support for static enforcment of concurrency safety and guaranteed isolation. I have found great joy in applying underlying concepts in more niche (and extreme) languages like Haskell to more mainstream languages like C#.  My favorite pasttime is tracing back the lineage of languages to their earliest ideas, especially when this leads to the unearthing of a subtle commonality among them. I have been designing one of my own and, while it is undoubtedly a 5-year project that may never see the light of day, I do it for the love of languages.

This book has been stewing inside me for a while now. And after seeing Guy L. Steele and Richard P. Gabriel's infinitely beautiful "50 in 50" presentation at JAOO this year, I decided it was time for it to escape.

Notation and Thought:
Behind Computer Science's Most Influential Programming Languages

     “That language is an instrument of human reason, and not merely a medium
     for the expression of thought, is a truth generally admitted.”
     --- George Boole, Laws of Thought

Programming languages are not only a notation for expression, but also a medium of thought, akin to the duality between natural written and spoken languages. If you can think it, you can create it. The reverse is also true: if a language poses impediments to your thought process, certain solutions to problems are simply unfathomable. Languages are therefore not just what you see “on paper”--each is a unique tool that can substantially limit, or expand, the creative freedom of the programmer in whose hands it sits. Good languages get out of the way, and great ones do a whole lot more.

In the early days, there was of course nothing that resembled modern day languages. Computers had to be told what to do in excruciating detail. One only has to look at modern day assembly language to see that programming a computer in this manner constrains creativity and slows progress. Alan Turing didn’t even have that when he wrote his classic On Computable Numbers with an Application to the Entscheidungsproblem paper, but he at least managed to solve some simple problems: by moving a tape reader and reading and writing symbols, he was able to create the modern day equivalent to subroutines and even add up a number or two. But our industry would have never seen radical advances in enabling technologies, and widespread computer use, that we enjoy today without significant advances in higher-order abstractions.

Plankalkül, or the plan calculus, is widely recognized as the first real programming language. It was designed by a German computer engineer, Konrad Zuse, and first written down in an unpublished manuscript in 1943. The language offered composite (albeit simplistic) data structures, arrays, named variables, subroutines, and moderately sophisticated control flow and looping constructs. Although it was never used in practice, Plankalkül was surprisingly ahead of its time. It was a big step towards more abstract problem solving.

It should be no surprise that subsequent programming languages are as varied in their design as the humans that created them. This fact can be seen by examining the ensuing decade of computing post-Plankalkül. The 1950s saw the invention of four new major languages that fundamentally shaped the future of language design. FORTRAN, or the FORmula TRANslation language, specialized in describing transformations on data and numerics, and was the first non- assembly language to reach widespread use in performance sensitive situations. LISP, or the LISt Processing language, was developed for symbolic processing and, eventually, found a home in artificial intelligence, pioneering many techniques that are still in use today such as first class functions as data, a recursive style of programming, and garbage collection. Its principles were derived from the mathematical logics of Alonzo Church and Haskell B. Curry, notably Church’s lambda calculus from the 1930s. ALGOL, or the ALGOrightmic Language, focused on describing algorithms elegantly, kick-started the imperative family of languages (of which many popular industry programming languages like C++ and Java are members), and later set the de facto standard style for Computer Science education curricula. Its method of encoding algorithms with assignments was far closer to the von Neumann architecture than was LISP, making the resulting programs behave predictably and efficiently. Lastly, COBOL, or the COmmon Business-Oriented Language, became the first domain-specific language (DSL) that targeted non-programming business and finance experts, broadening the general accessibility of computers. Each of the four has had a crucially important role to play in the history of programming languages.

There has been no shortage of language diversity after the birth of the initial four. In fact, hundreds of languages have since come and gone, some enjoying brief or extended periods of popular use. All that have since come have been deeply influenced by the pioneers, but have also contributed a handful of innovative new ideas that help programmers more clearly think about and express solutions to real-world problems. The lineage of languages has branched off into separately named family trees--such as imperative, functional, logic, declarative and domain-specific--only to reunite intimately with each other down the line. Indeed, it really is just one big happy family.

This book traces this lineage through the most influential languages--those that have deeply impacted the way that programmers think and write--and provides insight into the motivation behind them, their major influences, and the important features that each language contributed. Throughout, it is my hope to develop within the reader a new appreciation of the art of programming computers, an understanding of the impact that language has on our thinking, and an excitement about the future of language design that lies ahead.

Joe Duffy
November, 2008