Epigrams in Programming
"Epigrams in Programming" by Alan J. Perlis





1. One man's constant is another man's variable.

2. Functions delay binding; data structures induce binding.
Moral: Structure data late in the programming process.

3. Syntactic sugar causes cancer of the semicolon.

4. Every program is a part of some other program and rarely
fits.

5. If a program manipulates a large amount of data, it does
so in a small number of ways.

6. Symmetry is a complexity-reducing concept (co-routines
include subroutines); seek it everywhere.

7. It is easier to write an incorrect program than
understand a correct one.

8. A programming language is low level when its programs
require attention to the irrelevant.

9. It is better to have 100 functions operate on one data
structure than 10 functions on 10 data structures.

10. Get into a rut early: Do the same process the same way.
Accumulate idioms. Standardize. The only difference(!)
between Shakespeare and you was the size of his idiom list -
not the size of his vocabulary.

11. If you have a procedure with ten parameters, you
probably missed some.

12. Recursion is the root of computation since it trades
description for time.

13. If two people write exactly the same program, each
should be put into microcode and then they certainly won't
be the same.

14. In the long run every program becomes rococo - then
rubble.

15. Everything should be built top-down, except the first
time.

16. Every program has (at least) two purposes: the one for
which it was written, and another for which it wasn't.

17. If a listener nods his head when you're explaining your
program, wake him up.

18. A program without a loop and a structured variable isn't
worth writing.

19. A language that doesn't affect the way you think about
programming, is not worth knowing.

20. Wherever there is modularity there is the potential for
misunderstanding: Hiding information implies a need to check
communication.

21. Optimization hinders evolution.

22. A good system can't have a weak command language.

23. To understand a program you must become both the machine
and the program.

24. Perhaps if we wrote programs from childhood on, as
adults we'd be able to read them.

25. One can only display complex information in the mind.
Like seeing, movement or flow or alteration of view is more
important than the static picture, no matter how lovely.

26. There will always be things we wish to say in our
programs that in all known languages can only be said
poorly.

27. Once you understand how to write a program get someone
else to write it.

28. Around computers it is difficult to find the correct
unit of time to measure progress. Some cathedrals took a
century to complete. Can you imagine the grandeur and scope
of a program that would take as long?

29. For systems, the analogue of a face-lift is to add to
the control graph an edge that creates a cycle, not just an
additional node.

30. In programming, everything we do is a special case of
something more general -- and often we know it too quickly.

31. Simplicity does not precede complexity, but follows it.

32. Programmers are not to be measured by their ingenuity
and their logic but by the completeness of their case
analysis.

33. The eleventh commandment was "Thou Shalt Compute" or
"Thou Shalt Not Compute" - I forget which.

34. The string is a stark data structure and everywhere it
is passed there is much duplication of process. It is a
perfect vehicle for hiding information.

35. Everyone can be taught to sculpt: Michelangelo would
have had to be taught not to. So it is with great
programmers.

36. The use of a program to prove the 4-color theorem will
not change mathematics - it merely demonstrates that the
theorem, a challenge for a century, is probably not
important to mathematics.

37. The most important computer is the one that rages in our
skulls and ever seeks that satisfactory external emulator.
The standarization of real computers would be a disaster -
and so it probably won't happen.

38. Structured Programming supports the law of the excluded
middle.

39. Re graphics: A picture is worth 10K words - but only
those to describe the picture. Hardly any sets of 10K words
can be adequately described with pictures.

40. There are two ways to write error-free programs; only
the third one works.

41. Some programming languages manage to absorb change, but
withstand progress.

42. You can measure a programmer's perspective by noting his
attitude on the continuing vitality of FORTRAN.

43. In software systems, it is often the early bird that
makes the worm.

44.Sometimes I think the only universal in the computing
field is the fetch-execute cycle.

45. The goal of computation is the emulation of our
synthetic abilities, not the understanding of our analytic
ones.

46. Like punning, programming is a play on words.

47. As Will Rogers would have said, "There is no such thing
as a free variable."

48. The best book on programming for the layman is "Alice in
Wonderland"; but that's because it's the best book on
anything for the layman.

49. Giving up on assembly language was the apple in our
Garden of Eden: Languages whose use squanders machine cycles
are sinful. The LISP machine now permits LISP programmers to
abandon bra and fig-leaf.

50. When we understand knowledge-based systems, it will be
as before -- except our fingertips will have been singed.

51. Bringing computers into the home won't change either
one, but may revitalize the corner saloon.

52. Systems have sub-systems and sub-systems have sub-
systems and so on ad infinitum - which is why we're always
starting over.

53. So many good ideas are never heard from again once they
embark in a voyage on the semantic gulf.

54. Beware of the Turing tar-pit in which everything is
possible but nothing of interest is easy.

55. A LISP programmer knows the value of everything, but the
cost of nothing.

56. Software is under a constant tension. Being symbolic it
is arbitrarily perfectible; but also it is arbitrarily
changeable.

57. It is easier to change the specification to fit the
program than vice versa.

58. Fools ignore complexity. Pragmatists suffer it. Some can
avoid it.  Geniuses remove it.

59. In English every word can be verbed. Would that it were
so in our programming languages.

60. In seeking the unattainable, simplicity  only  gets  in
the way.

61. In programming, as in everything else, to be in error is
to be reborn.

62. In computing, invariants are ephemeral.

63. When we write programs that "learn", it turns  out  that
we do and they don't.

64. Often it is the  means  that  justify  the  ends:  Goals
advance  technique  and  technique  survives  even when goal
structures crumble.

65. Make no mistake about it: Computers  process  numbers  -
not  symbols.  We measure our understanding (and control) by
the extent to which we can arithmetize an activity.

66. Making something variable is easy. Controlling  duration
of constancy is the trick.

67. Think of all the psychic energy expended  in  seeking  a
fundamental distinction between "algorithm" and "program".

68. If we believe in data structures,  we  must  believe  in
independent  (hence  simultaneous)  processing. For why else
would we  collect  items  within  a  structure?  Why  do  we
tolerate languages that give us the one without the other?

69. In a  5  year  period  we  get  one  superb  programming
language.  Only we can't control when the 5 year period will
be.

70. Over the centuries the Indians developed  sign  language
for  communicating  phenomena  of interest. Programmers from
different tribes (FORTRAN, LISP, ALGOL, SNOBOL, etc.)  could
use  one  that doesn't require them to carry a blackboard on
their ponies.

71. Documentation  is  like  term  insurance:  It  satisfies
because  almost  no  one who subscribes to it depends on its
benefits.

72. An adequate bootstrap is a contradiction in terms.

73. It is not a language's weakness but its  strengths  that
control  the  gradient of its change: Alas, a language never
escapes its embryonic sac.

74. Is it possible that software is not like anything  else,
that it is meant to be discarded: that the whole point is to
see it as a soap bubble?

75. Because of its vitality, the computing field  is  always
in  desperate  need  of  new  cliches:  Banality soothes our
nerves.

76. It is the user who should parameterize  procedures,  not
their creators.

77.  The  cybernetic  exchange  between  man,  computer  and
algorithm  is  like  a  game  of musical chairs: The frantic
search for balance always leaves one of the  three  standing
ill at ease.

78. If your computer speaks English, it was probably made in
Japan.

79. A year spent in artificial  intelligence  is  enough  to
make one believe in God.

80. Prolonged contact with the computer turns mathematicians
into clerks and vice versa.

81. In computing, turning the obvious into the useful  is  a
living definition of the word "frustration".

82. We are on the verge: Today our program  proved  Fermat's
next-to-last theorem.

83. What is the difference between a Turing machine and  the
modern  computer?   It's  the same as that between Hillary's
ascent of Everest and the establishment of a Hilton hotel on
its peak.

84. Motto for a research laboratory: What we work on  today,
others will first think of tomorrow.

85. Though the Chinese should adore APL, it's  FORTRAN  they
put their money on.

86. We kid ourselves if we think that the ratio of procedure
to   data   in  an  active  data-base  system  can  be  made
arbitrarily small or even kept small.

87. We have  the  mini  and  the  micro  computer.  In  what
semantic niche would the pico computer fall?

88. It is not the computer's fault that Maxwell's  equations
are not adequate to design the electric motor.

89. One does not learn computing by using a hand calculator,
but one can forget arithmetic.

90. Computation has made the tree flower.

91. The computer reminds one of Lon  Chaney  --  it  is  the
machine of a thousand faces.

92. The computer is the ultimate  polluter:  its  feces  are
indistinguish- able from the food it produces.

93. When someone says "I  want  a  programming  language  in
which  I  need  only  say  what  I  wish  done,"  give him a
lollipop.

94.  Interfaces  keep  things  tidy,  but  don't  accelerate
growth: Functions do.

95. Don't have good  ideas  if  you  aren't  willing  to  be
responsible for them.

96. Computers don't introduce order anywhere as much as they
expose opportunities.

97. When a professor insists computer science is X  but  not
Y, have compassion for his graduate students.

98. In computing, the mean time  to  failure  keeps  getting
shorter.

99. In man-machine symbiosis, it is man who must adjust: The
machines can't.

100. We will never run out of things to program as  long  as
there is a single program around.

101. Dealing with failure is easy:  Work  hard  to  improve.
Success  is  also  easy  to  handle: You've solved the wrong
problem. Work hard to improve.

102. One can't proceed from the informal to  the  formal  by
formal means.

103. Purely applicative languages are poorly applicable.

104. The proof of a system's value is its existence.

105. You can't communicate complexity, only an awareness  of
it.

106. It's difficult  to  extract  sense  from  strings,  but
they're the only communication coin we can count on.

107. The debate rages on: is PL/I Bachtrian or Dromedary?

108.  Whenever  two  programmers  meet  to  criticize  their
programs, both are silent.

109. Think of it! With VLSI we can pack 100 ENIACS in 1  sq.
cm.

110. Editing is a rewording activity.

111. Why did the Roman Empire collapse? What  is  Latin  for
office automation?

112. Computer Science is embarrassed by the computer.

113. The only constructive  theory  connecting  neuroscience
and psychology will arise from the study of software.

114. Within a computer natural language is unnatural.

115. Most people find the concept  of  programming  obvious,
but the doing impossible.

116. You think you know when you can learn,  are  more  sure
when  you  can  write,  even  more  when  you can teach, but
certain when you can program.

117. It goes against the grain of modern education to  teach
children  to  program.  What  fun  is there in making plans,
acquiring  discipline  in  organizing   thoughts,   devoting
attention to detail and learning to be self-critical?

118. If you can imagine a society  in  which  the  computer-
robot is the only menial, you can imagine anything.

119. Programming is an unnatural act.

120. Adapting old programs to fit new machines usually means
adapting new machines to behave like old ones.
