Alan Perlis’s Programming Pearls

A LISP programmer knows the value of everything, but the cost of nothing. #programming #pearls

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

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

Systems have sub-systems and sub-systems have sub- systems and so on ad infinitum - which is why we’re always starting over. #programming #pearls

Bringing computers into the home won’t change either one, but may revitalize the corner saloon. #programming #pearls

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

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. #programming #pearls

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. #programming #pearls

As Will Rogers would have said, “There is no such thing as a free variable.” #programming #pearls

Like punning, programming is a play on words. #programming #pearls

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

Sometimes I think the only universal in the computing field is the fetch-execute cycle. #programming #pearls

In software systems, it is often the early bird that makes the worm. #programming #pearls

You can measure a programmer’s perspective by noting his attitude on the continuing vitality of FORTRAN. #programming #pearls

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

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

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. #programming #pearls

Structured Programming supports the law of the excluded middle. #programming #pearls

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. #programming #pearls

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. #programming #pearls

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

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. #programming #pearls

The eleventh commandment was “Thou Shalt Compute” or “Thou Shalt Not Compute” - I forget which. #programming #pearls

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

Simplicity does not precede complexity, but follows it. #programming #pearls

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

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. #programming #pearls

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? #programming #pearls

Once you understand how to write a program get someone else to write it. #programming #pearls

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

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. #programming #pearls

Perhaps if we wrote programs from childhood on, as adults we’d be able to read them. #programming #pearls

To understand a program you must become both the machine and the program. #programming #pearls

A good system can’t have a weak command language. #programming #pearls

Optimization hinders evolution. #programming #pearls

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

A language that doesn’t affect the way you think about programming, is not worth knowing. #programming #pearls

A program without a loop and a structured variable isn’t worth writing. #programming #pearls

If a listener nods his head when you’re explaining your program, wake him up. #programming #pearls

Every program has (at least) two purposes: the one for which it was written, and another for which it wasn’t. #programming #pearls

Everything should be built top-down, except the first time. #programming #pearls

In the long run every program becomes rococo - then rubble. #programming #pearls

If two people write exactly the same program, each should be put into microcode and then they certainly won’t be the same. #programming #pearls

Recursion is the root of computation since it trades description for time. #programming #pearls

If you have a procedure with ten parameters, you probably missed some. #programming #pearls

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. #programming #pearls

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

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

It is easier to write an incorrect program than understand a correct one. #programming #pearls

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