added preface for the ANS edition

\chapter*{Preface to the ANS \Forth{} Edition}\label{preface-ans}

\pagestyle{headings}

\initial The original 1984 \emph{Thinking \Forth} feels a bit dated

today. A lot happend with \Forth{} in the last 20 years, since this

book was first published. One of the most important is the ANS

\Forth{} standard from 1994. Unlike previous \Forth{} standards, it

provided necessary abstraction for machine word size and compilation

methods. Few \Forth{}s today are still indirect threaded code, and

even fewer are 16 bit systems.

What changed, too, is coding style. \Forth{} programs are rarely

written all uppercase these days. Like other languages that started

with uppercase keywords, the result are case insensitive systems---at

least for the ASCII subset of the character set.

Screens are no longer the dominant way to keep sources. Forth

development systems usually are hosted on a modern (large) operating

system, and most people keep their sources in files.

Operating systems now provide services to programs that weren't

possible 20 years ago, and modern \Forth{} systems must be able to use

them. Paradigms like object oriented programming were adopted to

\Forth{}.

All these changes demand a rewrite of this book. Since \person{Leo

Brodie} released the original under a Creative Commons license, this

is now possible. This edition adds all the missing things from the

original:

\begin{itemize}

\item Modify the example sources so that they run with ANS \Forth{}

systems.

\item Update coding style to current practice (lower case and such).

\item Add chapters about \Forth{} and OOP, \Forth{} debugging, and

maintenance.

\item Interview \Forth{} thinkers that didn't have a chance 20 years

ago.

\end{itemize}

\begin{flushright}

\vspace{5em}

\person{Bernd Paysan}

\vspace{2.5em}

\end{flushright}