178 Programming
we wrote a recursive-descent parser for Lisp. It took about 250 lines of C.
If the parser had been written in Lisp, it would not have even filled a page.The olden days mentioned above were just around the time that the editors
of this book were born. Dinosaurs ruled the machine room and Real Men
programmed with switches on the front panel. Today, sociologists and his-
torians are unable to determine why the seemingly rational programmers of
the time designed, implemented, and disseminated languages that were so
hard to parse. Perhaps they needed open research problems and writing
parsers for these hard-to-parse languages seemed like a good one.It kind of makes you wonder what kinds of drugs they were doing back in
the olden days.A program to parse C programs and figure out which functions call which
functions and where global variables are read and modified is the equiva-
lent of a C compiler front end. C compiler front ends are complex artifacts;
the complexity of the C language and the difficulty of using tools like yacc
make them that way. No wonder nobody is rushing to write this program.Die-hard Unix aficionados would say that you don’t need this program
since grep is a perfectly good solution. Plus, you can use grep in shell
pipelines. Well, the other day we were looking for all uses of the min func-
tion in some BSD kernel code. Here’s an example of what we got:
% grep min netinet/ip_icmp.c
icmplen = oiplen + min(8, oip->ip_len);
* that not corrupted and of at least minimum length.
* If the incoming packet was addressed directly to us,
* to the incoming interface.
* Retrieve any source routing from the incoming packet;
%Ye p , grep finds all of the occurrences of min, and then some.“Don’t know how to make love. Stop.”
The ideal programming tool should be quick and easy to use for common
tasks and, at the same time, powerful enough to handle tasks beyond that
for which it was intended. Unfortunately, in their zeal to be general, many
Unix tools forget about the quick and easy part.Make is one such tool. In abstract terms, make’s input is a description of a
dependency graph. Each node of the dependency graph contains a set of
commands to be run when that node is out of date with respect to the nodes
that it depends on. Nodes corresponds to files, and the file dates determine