hoc: Higher Order Calculator
Originally described in

Brian Kernighan & Rob Pike
The UNIX Programming Environment
Prentice Hall, Englewood Cliffs, NJ (1984)
Transcribed and updated for ANSI C by Aaron Katz (2011)

hoc is a simple language for computation.  Its main utility
is as a teaching tool, demonstrating the construction of a
software project of nontrivial scale and the use of tools
such as yacc, lex, and make (to this venerable list, I add
git).


In The UNIX Programming Environment, Kernighan & Pike
develop hoc incrementally, beginning with a very basic
implementation and gradually enhancing it with new features
and a more flexible architecture.  I have followed the steps
in the book, including the few features taht are left as
exercises for the reader.  Each "version" of hoc is labeled
with a git tag.  I have stayed faithful to the code printed
in the book, with a few exceptions:  I have completed the
exercises and from version 1 hoc has been able to read
commands from a source file provided as a command line
argument.  Perhaps most importantly, I have adapted the code
to conform to ANSI C (rather than the "K&R" style used in
the book and have made the necessary changes to quiet
warnings issued by gcc's highest warning level.

I have prepared this git repository mostly as an exercise
for myself to help in learning the use of yacc. It is my
hope that the curious programmer can see the evolution of
hoc as a series of patches.