The most surprising Unix programs

栏目: IT技术 · 发布时间: 4年前

[TUHS] The most surprising Unix programs

Doug McIlroy doug at cs.dartmouth.edu

Sat Mar 14 09:31:36 AEST 2020
Once in a while a new program really surprises me. Reminiscing a while
ago, I came up with a list of eye-opening Unix gems. Only a couple of
these programs are indispensable or much used. What singles them out is
their originality. I cannot imagine myself inventing any of them.

What programs have struck you similarly?

PDP-7 Unix

The simplicity and power of the system caused me to turn away from big
iron to a tiny machine. It offered the essence of the hierarchical
file system, separate shell, and user-level process control that Multics
had yet to deliver after hundreds of man-years' effort. Unix's lacks
(e.g. record structure in the file system) were as enlightening and
liberating as its novelties (e.g. shell redirection operators).

dc

The math library for Bob Morris's variable-precision desk calculator
used backward error analysis to determine the precision necessary at
each step to attain the user-specified precision of the result. In
my software-components talk at the 1968 NATO conference on software
engineering, I posited measurement-standard routines, which could deliver
results of any desired precision, but did not know how to design one. dc
still has the only such routines I know of.

typo

Typo ordered the words of a text by their similarity to the rest of the
text. Typographic errors like "hte" tended to the front (dissimilar) end
of the list. Bob Morris proudly said it would work as well on Urdu as it
did on English. Although typo didn't help with phonetic misspellings,
it was a godsend for amateur typists, and got plenty of use until the
advent of a much less interesting, but more precise, dictionary-based
spelling checker.

Typo was as surprising inside as it was outside. Its similarity
measure was based on trigram frequencies, which it counted in a 26x26x26
array. The small memory, which had barely room enough for 1-byte counters,
spurred a scheme for squeezing large numbers into small counters. To
avoid overflow, counters were updated probabilistically to maintain an
estimate of the logarithm of the count.

eqn

With the advent of phototypesetting, it became possible, but hideously
tedious, to output classical math notation. Lorinda Cherry set out to
devise a higher-level description language and was soon joined by Brian
Kernighan. Their brilliant stroke was to adapt oral tradition into written
expression, so eqn was remarkably easy to learn. The first of its kind,
eqn has barely been improved upon since.

struct

Brenda Baker undertook her Fortan-to-Ratfor converter against the advice
of her department head--me. I thought it would likely produce an ad hoc
reordering of the orginal, freed of statement numbers, but otherwise no
more readable than a properly indented Fortran program. Brenda proved
me wrong. She discovered that every Fortran program has a canonically
structured form. Programmers preferred the canonicalized form to what
they had originally written.

pascal

The syntax diagnostics from the compiler made by Sue Graham's group at
Berkeley were the mmost helpful I have ever seen--and they were generated
automatically. At a syntax error the compiler would suggest a token that
could be inserted that would allow parsing to proceed further. No attempt
was made to explain what was wrong. The compiler taught me Pascal in
an evening, with no manual at hand.

parts

Hidden inside WWB (writer's workbench), Lorinda Cherry's Parts annotated
English text with parts of speech, based on only a smidgen of English
vocabulary, orthography, and grammar. From Parts markup, WWB inferred
stylometrics such as the prevalance of adjectives, subordinate clauses,
and compound sentences. The Today show picked up on WWB and interviewed
Lorinda about it in the first TV exposure of anything Unix.

egrep

Al Aho expected his deterministic regular-expression recognizer would beat
Ken's classic nondeterministic recognizer. Unfortunately, for single-shot
use on complex regular expressions, Ken's could finish while egrep was
still busy building a deterministic automaton. To finally gain the prize,
Al sidestepped the curse of the automaton's exponentially big state table
by inventing a way to build on the fly only the table entries that are
actually visited during recognition.

crabs

Luca Cardelli's charming meta-program for the Blit window system released
crabs that wandered around in empty screen space nibbling away at the
ever more ragged edges of active windows.

Some common threads

Theory, though invisible on the surface, played a crucial role in the
majority of these programs: typo, dc, struct, pascal, egrep. In fact
much of their surprise lay in the novelty of the application of theory.

Originators of nearly half the list--pascal, struct, parts, eqn--were
women, well beyond women's demographic share of computer science.

Doug McIlroy 
March, 2020
More information about the TUHS mailing list

以上就是本文的全部内容,希望本文的内容对大家的学习或者工作能带来一定的帮助,也希望大家多多支持 码农网

查看所有标签

猜你喜欢:

本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们

算法竞赛入门经典

算法竞赛入门经典

刘汝佳、陈锋 / 2012-10 / 52.80元

《算法竞赛入门经典:训练指南》是《算法竞赛入门经典》的重要补充,旨在补充原书中没有涉及或者讲解得不够详细的内容,从而构建一个较完整的知识体系,并且用大量有针对性的题目,让抽象复杂的算法和数学具体化、实用化。《算法竞赛入门经典:训练指南》共6章,分别为算法设计基础、数学基础、实用数据结构、几何问题、图论算法与模型和更多算法专题,全书通过近200道例题深入浅出地介绍了上述领域的各个知识点、经典思维方式......一起来看看 《算法竞赛入门经典》 这本书的介绍吧!

URL 编码/解码
URL 编码/解码

URL 编码/解码

XML 在线格式化
XML 在线格式化

在线 XML 格式化压缩工具

HEX HSV 转换工具
HEX HSV 转换工具

HEX HSV 互换工具