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Re: [TUHS] Doug McIlroy's C++ regular expression library (mostly) revived

by Doug McIlroy

Why would anyone be interested in an old regex package that never was a part of any Unix distro? The driving force was Posix, whose regex spec was quite inscrutable. Could there be a reference implementation? It was easy to fool every implementation I could get my hands on, including Gnu's over-the-top 9000-line implementation. But as I got into it, I got fascinated by regexes per se. In making a recognizer, there's a tradeoff between contruction time and execution time. Linear execution can be achieved, but at a potentially exponential cost in construction time (and space). Backreferencing takes the regex languages out of the class of regular languages. Recalling that regular languages are closed under intersection and negation, I wondered about how to implement new regex operators, & and -. I came up with a scheme for this optional non-Posix feature that involved layering continuation-passing over more traditional methods. And while I was at it, I broke out smaller sublanguages for special treatment (as does Gnu), all the way down to Knuth-Morris-Pratt for expressions in which the only operation is catenation. And finally, having followed the development of C++ from its infancy, I wanted to try out its new template facility, so there's a bit of that in the package, too. Arnold has discovered that not only has C++ evolved, but also that without the discipline of -Wall to force clean code, I was rather cavalier about casting, both explicitly and implicitly. The only real customer the code ever had was the AST project, which translated it to C. After the C++ had sat idle for a half-dozen years, I thought to revive it in Linux, but found it riddled with incompatibilities with that new environment and gave up. Arnold deserves a citation for bravery in pushing that through 15 years further on. Doug

6 years, 8 months

In Memoriam: Per Brinch Hansen

by Dave Horsfall

[ I've always posted these to TUHS with no objections, so I have no idea whether COFF would be a better forum; feel free to spank me (I might even enjoy it!) ] We lost Per Brinch Hansen, a computer scientist, on this day in 2007. He specialised in operating systems and concurrent programming, and wrote the classic book "Operating System Principles" which was published in six languages for decades. He also wrote another book "The Architecture of Concurrent Programs" which demonstrated an entire operating system written in Concurrent Pascal (much like the Lions' books on Unix). -- Dave

6 years, 8 months

That tour through the C compiler...

by Dave Horsfall

My DuckDuckGo-fu appears to be on the blink (and I refuse to use Google out of privacy concerns); is there a PDF/PS/groff somewhere? I don't use fancy-wanky markup languages. Thanks. -- Dave

6 years, 9 months

Re: [TUHS] Looking for final C compiler by Dennis Ritchie

by Paul Ruizendaal

> Thank you for the info - I will certainly look at the USENIX tapes. > > I will try to port the C compiler to amd64 - while preserving as much of > the original code as I can. But not sure if this is even feasible. > > Thanks and Regards > Dibyendu If that is your goal, you might want to start with the version included with 2.11BSD. It is essentially the same as the version from V7, but with 15 more years of bug fixes. I used that source to port V6 Unix to the TI990 architecture back in 2014/2015 and the good thing about it is that it still compiles with a modern gcc. For your project, I think you would be able to use the first pass ‘c0’ almost unchanged. The second pass ‘c1’ would need major restructuring. It mainly builds a tree for each expression and then performs various transformations, many of which are PDP11 specific (but also portable ones, like handling of constant expressions). It then covers the tree with code fragments selected from a library. This library (‘optable') would need a full rewrite as well. The last pass ‘c2’ is the optimiser and is also highly PDP11 specific. It reads the assembler output of ‘c1’ function by function, building an instruction list. It then performs some portable optimisations (eliminating unnecessary jumps, etc.) and also more PDP11 specific optimisations (the most complex being removing redundant register loads - the concept of which would be reusable). There are about 12,000 lines of code and as a rough guess I would say that some 40% needs rewriting. A new code fragment library would probably be some 2 to 3 thousand lines. I recall reading about a project to revive the Ritchie C compiler one or two years ago, but a quick web search came up dry. Anybody else remember reading that?

6 years, 9 months

Frank Heart, Who Helped to Design the ArpaNet IMPs at BBN Dies at 89

by Clem Cole

Note the NY Times head lines this as 'pre-Internet' which is a little sad, but what can you do: https://www.nytimes.com/2018/06/25/technology/frank-heart- who-linked-computers-before-the-internet-dies-at-89.html

6 years, 9 months

Doug McIlroy's C++ regular expression library (mostly) revived

by Arnold Robbins

Hi All. I have (mostly) revived Doug McIlroy's C++ regular expression parsing library. I gratefully acknowledge and thank him for allowing me to publish the code and for his help in finding all the bits and pieces. It's available at https://github.com/arnoldrobbins/mcilroy-regex . The main things I've done are to gather all the bits and pieces, rename files to have a .cpp extension, and get everything to compile using current g++ and standard make. I'm at the point where I could use some help. The various tests do not all run successfully. 1. make retest - a number of tests fail 2. ./tesgrep.sh - a number of tests fail 3. ./testsed.sh - tests fail with core dumps Looking briefly, some of the code in sed plays C games, casting various things arouond to pointers of different types and dereferencing them; these things tend to cause trouble in C++. I'm hopeful that more eyes on this code will help it come back to life more quickly. Any and all help will be appreciated. Thanks, Arnold P.S. Let's not start a flame war about C vs. C++ etc. etc. If you can help, please just dive in. Otherwise, just go, "wow, neat work" and move on to something else. :-) Thanks.

6 years, 9 months

Speaking commands [Was: Bell System Technical Journal archive]

by Nemo

On 15/07/2018, Warren Toomey <wkt(a)tuhs.org> wrote (in part): > Also: > https://www.youtube.com/watch?v=NTfOnGZUZDk > > Where GREP Came From - Computerphile (with Brian Kernighan) I was intrigued by BMK's comment that "ed" was never spokend as "ed" by "those in the know", which leads me to wonder how things were spoken. Here is a litte list of how I pronounce things [with others' versions in brackets]. Others will no doubt be aghast. ls - "list" sometimes "l s"; rm - "remove"; chmod - "change mode" [but I have heard "ch-mode"] ar - "archive" [others have said "arrr"] N.

6 years, 9 months

Looking for final C compiler by Dennis Ritchie

by Dibyendu Majumdar

Hi I am interested in finding out if the last C compiler code (not the earliest versions which I know are available) written by Dennis Ritchie is available somewhere. I assume that the C compiler in V7 code was written by him? Thanks and Regards Dibyendu

6 years, 9 months

grep

by Paul Winalski

On 7/18/18, Doug McIlroy <doug(a)cs.dartmouth.edu> wrote: > > The famous exception is grep, which became a verb. I think the similarity to "grab" and "grope" helped. > "grep for" and "grep out". "grep for" I'm familiar with. What does it mean to "grep out"? -Paul W.

6 years, 9 months

Re: [TUHS] TUHS Digest, Vol 32, Issue 12

by Doug McIlroy

Arnold was clerly on the Unix Room wavelength. ^All those two-letter commands were spelled out in conversation, even m-v. The pronunciation of rmdir was hybrid: r-m-dir. But when one talked about an action--not a command per se--verbs would be used: move or copy a file, list a directory. The famous exception is grep, which became a verb. There was no snappy ready-made verb that covered all the aspects of its use: search for mentions in one file, find files that mention, look for patterns, filter data, check for malformed data, ... The verb had two idiomatic variants, "grep for" and "grep out". Doug

6 years, 9 months

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