Kent M. Pitman's Second Wind

Kent M. Pitman has already given you his first 11 answers to the questions you asked him about Lisp, Scheme, the creation of programming standards, and much more -- below are his answers to another eight (starting with answer #12). Thanks again, Kent.

12) Good texts for learning Scheme?
by drenehtsral

I have recently been working on learning Scheme in my spare time, with the eventual goal of writing a scheme based scripting system to run the guts of a massive adventure game/graphical mud sort of system, everything from environment simulation (predator/prey cycles, etc...) to 3d models (i.e. models will be geometry glued together by scripts so you could have trees that by a random seed and a growth level variable have grown over time and are unique to provide interresting landscape features). Scheme is appealing because it's simple, powerful, and adapts well to the idea of a threaded interpreter.

To further my goal of learning Scheme inside and out, I've been reading "The Little Schemer," as well as "Structure and Interpretation of Computer Programs." Do you have any other recommendations for good Scheme programming texts?

Kent M. Pitman: You can get a list of textbooks from Schemers website. If you can articulate a particular need or preference that you think should help narrow down the many available choices, I'd suggest posting a more specific inquiry to the comp.lang.scheme newsgroup.

13) Overlooked practical aspects of Lisp
by hding

Why do you think that people so often overlook many of the wonderful things in Common Lisp such as unwind-protect, the whole condition system (which you are of course closely associated with), and so on - things that make it very useful for day-to-day programming, and are there any such things that you'd particularly highlight, or conversely that you wish had become part of the standard but did not.

Incidentally, thank you for all of the insight so generously and regularly poured forth in comp.lang.lisp.

KMP: Well, people program with tools that are familiar to them. Unless Common Lisp is someone's first language, it'd be easy for them to overlook the things it contains that are not like the things they're familiar with. There's a certain irony here because often the reason people will leave a language for another language is that they've reached the limits of what they can do with the first language and they need more power. So you'd expect that they'd aggressively look for features of the new language that were different than the things they've used before. And probably some do. But you're right that others cling to the safety and familiarity of the operators they could just as well have found in the old language they left behind, and so in the process they miss out on what the language can offer them.

Fortunately, unwind-protect is finally (pardon the pun) present in Java. And some hints of the Common Lisp condition system made it into Java as well. So probably people who come to Common Lisp from Java will be inclined to seek out those capabilities. But there's a lot of other stuff there and I hope new users will indulge their curiosity and take the time to explore.

As to what we should have in the language, the main omission of note is some sort of system definition tool (the in-Lisp analog of make). It was a shame that we did a feature-freeze on ANSI Common Lisp in 1988 but didn't get the standard out until 1994, and the suggestion of including such a tool didn't come until the after-freeze period. All vendors offer such a facility, but programs would be more portable if there were a uniform solution.

There are also quite a number of things about Common Lisp that are available in the same or similar forms in nearly all implementations. Multi-tasking, sockets, database access, external function call, windowing, and so on. It wouldn't be bad to have included any of these, but the fact is that they weren't ready for standarization in 1988. At this point, though, I think other mechanisms than standards are the right way to proceed.

The Lisp community used to expect the delivery mechanism for new functionality to be a new language spec. But that requires working through consensus standards bodies. The problem is that, by their nature, standards bodies are synchronization mechanisms. The problem with synchronization mechanisms in a massively parallel world is that they slow things down. The world is not going to wait for us to slow down, so I think we need to evolve mechanisms that will keep up better with a degree of pace that is externally dictated.

I think this is an area where Lisp as a community has been slow to respond. There need to be community mechanisms for sharing the many great commercial and private packages people have been creating in Lisp, so that we can properly reap the cross-product benefits of our community's productivity. I see evidence that this is changing. The Common Lisp Open Code Collection (CLOCC) is one such mechanism that addresses open source code. I'd like to see similar mechanisms arise for the exchange of proprietary products as well.

As to my posts on the comp.lang.lisp newsgroup, thank you. I'm glad you enjoy them. Frankly, I always consider it a victory to hear I haven't bored everyone to death. In background I've been working on putting together several books on Lisp, but one never quite knows if one will finish such things. I regard comp.lang.lisp as a kind of insurance policy, assuring that at least some piece of what I have seen and done in my career gets transferred from individual memory to global group memory.

I think preserving individual experiences for history is quite important. In the future, this will happen naturally due to logs kept by online collaboration tools. But I'm especially worried about the records of what happened between about 1960 (the birth of programming languages) and 1994 (the birth of the web). Most of everything in that time range is recorded on paper and will eventually be lost. Looking back from the future, I expect it to be as confusing to figure out how the information society was born as it is to look back in a telescope to see the birth of the Universe. You'll get very close, but then you'll get to a point where you can see nothing. The informational big bang. I've been working on webbing all of my old hardcopy papers, and I hope others of that era will commit to doing the same.

14) Lisp - Scheme - ML
by Tom7

I know a lot of big academic (erstwhile) lisp shops, such as CMU, have transitioned away from lisp to ML [standardml.org] and relatives [inria.fr]. Some of the reasons we might give are:

• Sophisticated type systems, catching most bugs before your program is run, ensuring safety, etc.
• Much more efficient (http://www.bagley.org/~doug/shootout/craps.shtml), partly due to compilation strategies using types
• Increased modularity and abstraction
• Pattern matching, (subjectively) more natural syntax

In fact, I'm one of those people. I've been scoffed at by lisp fans, but most had never used ML. But I have an open mind, so, in the face of more "modern" languages, what advantages do lisp and scheme offer? Do you think that these advantages are fundamentally impossible to achieve in a typed setting?

KMP: First, I assume by "typed" you mean "statically typed." I think of Lisp as "dynamically typed." I think of most machine languages as "untyped." I've heard statically typed languages sometimes called strongly typed, and I sometimes use this terminology myself out of habit, but I've grown to dislike it because it seems to me that the issue of strength ought to refer to whether you check types, not when you do. The terms "static" and "dynamic" seem to me to better get to the heart of the matter.

To quote Abraham Lincoln, admittedly somewhat out of context, "People who like this sort of thing will find this the sort of thing they like." So to somewhat flippantly re-interpret Lincoln's remarks in a modern context, applying perhaps just a bit of obligatory political spin to the result: The fact that functional languages appeal to people who like functional languages is not a proof that functional languages are of general purpose appeal.

I think the real reason that CMU (or any university with a grant-based funding model) changed its direction is good sources of funding in research depend on saying you're doing something "new and different." Such a shift doesn't imply that the thing left behind wasn't "tried and true," but only that "tried and true" is not what gets research dollars. Research must constantly stir the mix, but that doesn't imply obsolescence to what came before. So don't read too much into that.

Answering each of your points in detail might require a whole article, but I'll touch on each in brief:

• Sophisticated type systems, catching most bugs before your program is run, ensuring safety, etc. Much more efficient partly due to compilation strategies using types.

  Actually, it's funny that you both mention the CMU project and then make this comment. Before moving away from Common Lisp, the CMU crowd was successful in demonstrating to the Lisp community's satisfaction that there were enormous opportunities offered by the Common Lisp language design in terms of type inferencing that still today go untapped by implementations. This is really a market issue, not a language design issue. The fact is that although other languages do a lot more type inferencing, vendors are not getting huge numbers of bug reports saying that better type inferencing is what stands between programmers and the commercial success of their product. Over time, I think you'll see more and more interesting type analysis done, but such work is always balanced against other needs of users, such as CORBA, COM, RMI, and web interfaces, for example, such as UI toolkits and debugging options. When I observe, as I often do, that languages are political parties, this is what I mean. They are each responsive not to the needs of the world, but to the needs of their constituencies. And the Lisp constituency, while it is not oblivious to the value of type inferencing, does not see that issue as its number one priority.

• Increased modularity and abstraction.

  This is quite a multidimensional space. I think Lisp provides great opportunities for modularity and abstraction that other languages do not. And yet, there are sometimes things I can't abstract as well as I wish. An example of a minor omission: Common Lisp's CLOS doesn't do protocol abstraction as well as Zetalisp's New Flavors; among other things, one can't declare that certain unimplemented methods are required. But with the use of the macro system and the Meta-Object Protocol (MOP), one can add this kind of thing. Further, the package system is missing certain kinds of inheritance capabilities I've often wished for, but I recently sat down and did the work of writing my own versions of defpackage for my own use, adding the capabilities I wanted in a way that my own tools can use, and I had no difficulty. For the most part, I've found the limitations of Common Lisp's abstraction capabilites to be incidental, and not deep, and I've found its syntactic reorganization capabilities more than capable of making up for it.

• Pattern matching.

  I think you're right that Lisp doesn't do pattern matching. Whether or not that's a good or bad thing is subjective. I think there are people who like pattern matching and people who don't. In fairness to Lisp, though, on the few occasions in my career where I've felt a strong need for pattern matching, I've been able to implement it easily. And, importantly, Lisp's syntactic adaptability has allowed me to make my personal implementation look as natural in the programs I write as if it were natively provided by the language; most other languages don't give me the syntactic control to be able to add new functionality in a way that feels appropriate to the language. So personally, I don't find this a strong negative; rather, I see it as an opportunity for you to create a layered library that supports the needs of yourself and others like you.

• (Subjectively) more natural syntax.

  I don't think you can make the case that much of any language has "natural" syntax. COBOL and HyperTalk gave this the fairest shot and there's a big difference even between them and any natural language. I personally find Lisp syntax remarkably natural in that it focuses on symbols that you could say out loud, marking them minimally to indicate grouping. Other languages contain lots of special-purpose markers like commas, semicolons, asterisks, and braces/brackets/parens that are used in quite nitpicky ways. All this to say that you're right on this one: it's subjective. And as such, I hope I can fairly dismiss this as an even draw.

15) Lisp in Mathematics Programming
by An Anonymous Coward

Gregory Chaitin has a book called "The Limits of Mathematics." In it he claims that mathematicians should love Lisp because Lisp is basically set theory, and all mathematicians love set theory. I wholeheartedly agree with this, one only needs to look at Chaitin's Lisp programs to realize how quickly and succinctly one can arrive at astonishing incompleteness results in mathematics. So we know Lisp is great for stuff like this, really researching a mathematical subject. Do you see Lisp continuing in this direction, showing and discovering theorems, or will it move into industry? Or has it moved into industry, and we just don't know it? Do the likes of NASA and JPL use Lisp and Scheme religiously? I would bet so.

KMP: Lisp may have started out as a way of addressing abstract topics like math (logic, calculus, prime numbers, etc.) and artificial intelligence, but it long ago made the transition to commercial applications. Both Scheme and Common Lisp have been and continue to be used in real-world applications that might surprise you. These include (but are certainly not limited to) applications in airline scheduling, commercial database manipulation, computer operating systems, bioengineering, web services, document format translation, and, yes, even space exploration. Franz, Inc. has created quite a nice page of Lisp success stories that I think expand on this much better than I could in the space I've allowed myself to answer this question. And speaking of NASA/JPL, they did a comparative study of Lisp vs Java and C++ that some might find interesting.

16) Scheme in CS
by An Anonymous Coward

It seems many of the more popular CS programs in the world use Scheme as a teaching language. A lot of times, students complain about this, saying they'd prefer to learn about C or another language that is considered "apt for industry." I used to be like this too, but have now discovered the error of my thinking. How have you convinced others that while the latest programs might not be written in Scheme, that it is worth a student's time to learn Scheme. Many seem stuck to the point that if they won't use it outside of school, they shouldn't learn it. How can we convince them otherwise, to become scholarly citizens instead of drones?

KMP: I think the thing to explain to a student is that the world is ever changing and that one cannot put ones eggs all in one basket. Furthermore, modern environments are often quite heterogeneous, with different languages and systems being used together cooperatively. Especially for a CS student, who often has the luxury of time that a person in the job world does not, I think it's worth taking time to learn as many different languages as possible. This not only exposes the students to alternate ways of thinking, but it also prepares the student to quickly change modes of thought or languages of expression later. Once on the job, one often can't afford the ramp-up time to learn a new language at the point it becomes necessary to use. Better to already know it and just have to "brush up".

One is much more likely to consider alternative approaches if one has a sense of what is involved in them; it's very easy to fear the unknown, even when the unknown might be of great help. So get to know as many things as you can while you can. Common Lisp and Scheme, which I regard as two very different languages, by the way, should definitely be among the things every student studies. But they should not be the only things the person studies. Like it or not, there is a lot the professional programmer needs to know to be really successful not just tomorrow, but for a lifetime.

As Oliver Wendell Holmes is often quoted as saying, "A mind stretched to a new idea never returns to its original dimensions." In order to stretch a student's mind, I recommend they make a list of "kinds of languages" and then learn as many different kinds as they can. Here are some that come to mind, though I'm sure others with different experience than me might reasonably contribute still others.

• A block-structured language, such as Algol or Pascal or Scheme.
• A line-oriented language, such as Fortran or BASIC.
• A rule-based logic language, such as Prolog or EMYCIN.
• An Englishy language such as HyperTalk or Cobol.
• A "stack" language such as PostScript.
• A "line noise" language (heavy emphasis on one-letter operators) like APL or Teco.
• A dynamic object-oriented language, such as Common Lisp or Smalltalk .
• A strongly-typed, statically analyzed language such as ML or Haskell.
• A dynamically-typed functional programming language, such as Scheme.
• A string or macro processing language, such as Perl or m4 or TeX or Teco.
• A database access language, such as SQL.
• An abstract high-level, assembly language, such as Java.
• A concrete high-level, assembly language, such as C.
• A low-level, traditional assembly language.
• A scripting language, such as Javascript.
• An interface-definition language such as Visual Basic, HyperTalk, or Javascript.
• A document-structuring language such as XSL or TeX.
• A language with a modern error system, such as Common Lisp or Dylan.
• A reflective/introspective language such as Common Lisp or Java.
• A symbolic programming language, such as Common Lisp or Scheme.
• A security-oriented language, such as Java or MOO.
• A language where both programs and data are fully persistent, such as MOO or HyperTalk.

I'm confident that if people make a sincere effort to learn each of these kinds of languages on their own terms, the Lisp community will get its share of converts. But further, I would hope that the people who come to the Lisp community bring with them the ideas of other communities so that we can incorporate, rather than hide from, the good ideas that we need in order to continually be moving forward.

17) A question for Kent
by MarkusQ

Do you have a maclisp manual I could borrow?

KMP:For those not familiar with Maclisp, it's a defunct dialect of Lisp that predated and strongly influenced the design of Common Lisp.

I've been working on webbing The Revised Maclisp Manual, which I had published on paper back in the early 1980's. It's not quite ready to go out yet, but should finally be ready sometime in the not terribly distant future. Probably a month or two. Watch the site maclisp.info for more information.

18) Open Implementations
by Martin Pomije

What is your opinion of the idea of Open Implementations from Gregor Kiczales? Do you think that his idea could help Lisp be more widely used?

You can see him giving a lecture about this idea here. [microsoft.com] The video is only available in Windows Media format on this site.

KMP: I hadn't seen Gregor Kiczales's talk on Open Implementations, so I enjoyed watching it. Thanks for the pointer!

The talk made me think back to various related ideas I've seen batted around for a long time, the earliest of which that I can recall is a short paper on something called "Capsules" (an object system where classes were allowed to have multiple implementations) by Richard Zippel back in the late 1970s or early 1980s at MIT. Often, especially in a university environment, people will make up such a concept, bat it around for a bit, and then go on to something else. There are some very interesting ideas there and I'm glad to see that they're being pursued seriously, especially by someone as thoughtful and talented as I know Gregor to be.

As a formalized area of study, this topic of "aspect-oriented programming" is new to me. It reuses some old ideas in new ways, and introduces some new ones along with it. I'm only just barely becoming conversant in the terminology, so I can't really speak to it from a theoretical point of view. But it looks promising. And from a practical point of view, I can note that I'm getting daily on-the-job training in it through my consulting relationship with The Software Smith. They're using Lisp as a vehicle to apply the principles of aspect-oriented programming, and the results they get are quite spectacular.

19) What was up with CLisp's "loop" form?
by Jayson

Did you can have anything to do or know who had anything to do with the "loop" form in Common Lisp? Why does it look and feel just like a FOR loop on C (from the Graham book):

(loop for x = 8 then (/x 2)
until (< x 1)
do (princ x))

This is one of by biggest minor nags about CLisp and I am very curious what was going through the committee's collective head. Didn't anybody balk at this enough to at least get the syntax cleaned up?

KMP: The example you cite is quite simplistic and if this were the only reason for using LOOP, we wouldn't have it. Lisp has a number of other iteration operators for doing simple loops like this. However, the reason for using LOOP is that it can represent much more complicated arrangements of iteration paths and collection techniques. I used to grumble a lot myself about how "un-Lispy" LOOP seemed, but over time I come to the belief that the benefits outweigh the costs. A loop like this:

(loop for x from 0
for y in some-list
when (good-result? y)
collect (list x y))

is easy to write and maintain, and much easier to explain than the equivalent, but more Lispy:

(do ((x 0 (+ x 1))
(y-list some-list (cdr y-list))
(result '()))
((null y)
(nreverse result))
(let ((y (first y-list)))
(when (good-result? y)
(push (list x y) result))))

The Common Lisp community likes to offer the traditional Lispy notations for places where they enhance readability, but we also offer alternative notations for situations where we've learned there's a call for it. We leave the choice of which style to use up to the individual taste of the programmer. Common Lisp is not a minimalist language offering only one way to do things or rigidly attempting to force people into a single programming paradigm.

By the way, this is a fundamental difference between the ANSI Common Lisp design philosophy and the Scheme design philosophy. The introduction to the Scheme specification states:

Programming languages should be designed not by piling feature on top of feature, but by removing the weaknesses and restrictions that make additional features appear necessary. Scheme demonstrates that a very small number of rules for forming expressions, with no restrictions on how they are composed, suffice to form a practical and efficient programming language that is flexible enough to support most of the major programming paradigms in use today.

By contrast, the charter for X3J13, the group that designed ANSI Common Lisp, stated the following in the X3J13 charter:

It will codify existing practice, provide additional features to facilitate portability of code among diverse implementations, and establish normative Common Lisp programming practice. The committee will begin with the language described in Common Lisp: The Language by Guy L. Steele Jr. (Digital Press, 1984), which is the current de facto standard for Common Lisp. Whenever there is a proposal for the standard to differ from Common Lisp: The Language, the committee shall weigh both future costs of adopting (or not adopting) a change and costs of conversion of existing code. Aesthetic criteria shall be a subordinate consideration.

In other words, the Scheme community is a very conservative community that is highly focused on keeping its language specification as highly aesthetic and minimal in size as possible. By contrast, the Common Lisp community is an industrial standard that is concerned with messier issues of compatibility, portability, and commercial need; while the Common Lisp community cares about aesthetics, it does not allow aesthetics to dominate practicality as a design criterion.

The relevance of this here is that the Lisp family of languages is made up of a number of smaller communities who share a few core ideas, but really have some very divergent points of view. Each is worthy of study in its own right. One should not, having looked at Scheme, assume they have good intuitions about Common Lisp, nor vice versa.

Comments

Re:Large-scale Lisp projects?

[WillWare]

are there really people implementing large systems using Lisp?

Here are some, and some more, and a few others.

Thanks Kent

[dlakelan]

Thanks again for your two part series. As someone who took to scheme immediately as soon as I saw it, and moved into Common Lisp with enthusiasm when I found it, I am familiar with these types of questions.

I especially think your description of a list of language types to learn is valuable to those who haven't had the experience of learning multiple languages.

I want to address a few questions I've heard frequently myself.

1) Why learn XYZ it won't help me get a job or won't be used on the job.

The fact of the matter is that the more you know about how computations CAN be described, the more you will know about what the right way to describe a *particular* computation is. This means when someone comes to you with 150 pages of code in straight C that implements a simple data format parser, or a preferences file reader, or a layout engine for a diagram editor or whatever, if you have seen 5 or 6 different styles of languages and techniques for programming, you will be able to decide how best to attack the problem that needs solving.

Often with the right point of view, a problem becomes an order of magnitude simpler. The beautiful thing about LISP is that it gives you the ability to take so many different points of view within a single language.

I still use flex/YACC, and M4, and sed, shell scripts, and will occasionally write some C/C++ (usually to link into lisp at a hotspot :-)) but when I approach a problem I always think to myself "what is the best way to look at this problem to make it simpler to solve". Often LISP lets me express that solution better than other systems.

This approach is basically the same approach a mathematician takes to proofs and problem solutions. Make the problem smaller, make it more like something we know how to solve...

Here's the other one I hear often:

2) We can't use XYZ there aren't enough people who know XYZ to support it. Go back to (or stick with) C/C++/Java/Perl!

This simply is a way to dodge having to rationally consider a different language or system. The fact of the matter is:

a) Just because you can hire someone who claims to know C/C++ or whatever, doesn't mean you can hire someone who can solve your problem! Programming involves a lot more than just knowing the syntax of a given langauge, and some of the features the library offers.

b) If by switching to something else you can make your problem several times easier, then the cost of training every good candidate vs. sticking to your old ways is essentially negative!

Most of the time, spending a few weeks of training your new candidate in how your system works will pay off big-time when it comes to debugging, quality assurance, adding new features, and even implementing the feature you initially hired them for. Why? Because understanding the PROBLEM and the solution method is much harder than understanding the language syntax, or even most language semantics.

I run my own business, it's just me. My ability to understand a problem, work with people to figure out good implementation strategies, and write code in LISP to rapidly create the products and services I want to provide are all advantages that I got by learning many languages, and especially LISP family languages.

thanks again Kent!

Re:Large-scale Lisp projects?

[Anonymous Coward]

and yet a few more (Xanalys). The NASA remote agent is particularly interesting.

Re:How many more questions/answers are there?

[NetSettler]

I gave timothy all answers at once, but there was a fixed data limit on the size of an article, so he had to post it in two parts. I had no idea this wasn't a typical length; I just wanted to make sure that everyone's question was answered fairly. My thanks to those interested enough to stop back and read along on this second set.

Re:Precedence and Associativity cause Unreadable C

[SimHacker]

The ScriptX programming language from Kaleida was like what you describe: essentially a multimedia object oriented cross platform lexically scoped Lisp, Scheme or more specifically Dylan, but with a simple, more traditional surface syntax.

The ScriptX parser allowed you to type in a straightforward javascript-like syntax, with traditional infix notation, precedence rules and other additional syntactic sugar.

The parser transformed text into a parse tree, that was like Lisp s-expressions. ScriptX macros operated in terms of those parse trees, not the surface syntax. So internally it even had "downward passing" continuations (that you couldn't pass outside of the scope they were created), but the parse trees were compiled into a byte code, not unlike the Java virtual machine (which explains why it didn't support fully general continuations).

So you could implement any number of different surface syntaxes for ScriptX, by writing different parsers. My trusty Kaleida colleague DanFuzz wrote a traditional Scheme parser for ScriptX.

ScriptX was a lot like Dylan with a cross platform multimedia class library. It was essentially a Lisp-like language, designed around an object system and class library, more dynamic like CLOS than static like Java. Unlike Java, all data types including integers and arrays are first class objects.

ScriptX had a rich set of polymorphic container classes, much more dynamic than STL, that made heavy use of multiple inheritance.

The container classes (like arrays and maps) were supported by the language sytax, and mixed into many system classes, so you could easily treat windows as arrays, looping over their subwindows, filtering collections of objects through functions and type conversions with "pipes", mix collections into your own classes so they're easy to use through well supported interfaces, etc.

ScriptX had built-in high level time synchronization and graphics classes, including QuickTime movies, sprite graphics like Director, and vector graphics similar to Flash.

One of the great things about ScriptX, which also applies to CLOS and Dylan which inspired it, is its wonderful dynamic objects system. Programming in C++ and STL is totally miserable after having been exposed to ScriptX and CLOS.

For example, I subclassed ScriptX container classes like Array to implement ScriptX Classes for automatically generating HTML, that macros can plug together like legos and dynamically expand into complex web pages.

The ScriptX Tracking Service is a good example of using multiple inheritance with the container and presentation classes.

There's an abstract class called Tracker (that inherits only from RootObject): "This mixin class gives an object the ability to track the mouse, by participating in the tracking service protocol. You can mix Tracker in with presentation and model objects to implement all kinds of direct manipulation interfaces.".

The abstract Tracker class is subclassed by the concrete leaf class TrackerCachedPresenter, and also by another abstract class, TrackerMulti, which implement the recursive tracking protocol. TrackerMulti is then mixed down into concrete with the various container presentation classes TrackerMultiPresenter, TrackerGroupPresenter and TrackerTwoDSpace.

ScriptX was great fun to think and program in. It was an ideal language for developing an open ended platform for plugging together dynamically loaded interactive multimedia objects like Legos.

At the time (1995), Java was no nowhere near capable of doing anything like that on the Mac, Windows and OS/2. With regard to more modern languages, Python is most exciting dynamic and practical programming language around.

The best thing about Python, is that it's completely open source.

It's not tightly controled by a short sighted company that only intends to use it in their religious Jihad against Microsoft, like Java.

And it's not proprietary, jointly developed by strange bedfellows Apple and IBM, and swept under the rug, like Kaleida's ScriptX was.

So Python will be around forever, while quickly and naturally evolving, because it has earnestly learned so many lessons from Lisp and other languages.

Q: What do you get when you cross Apple and IBM?

A: IBM.

-Don

Re:Precedence and Associativity cause Unreadable C

[NetSettler]

Re: I haven't done usability testing with programming languages. But I can guess what you'd find if you did:

• One statement per line aids readability.
• 30 lines of short, simple statements are easier to read than 10 longer, more complex lines.

I'm not into hard-and-fast rules but I don't think these two points are radically inconsistent with most style I see observed in Lisp code. Lisp doesn't have a statement concept, but things very like statements do typically occur on their own line. People don't start blocks and put all the subexpressions on one line, though they could. So, to be honest, I have no idea what you're getting at here. I see nothing Lisp does to really push against this issue one way or another. The comment seems equally applicable to C, even though there, too, people by choice tend not to do the thing the language would let them and that you seem to fear.

• A distinction between statements and expressions aids readability.

Of your various "style rules", this is the only one that I could clearly say there's a parting of opinion on. Now, I know parsing reasons for making this distinction. And perhaps there are teaching reasons. But I've never heard it asserted that this was a readability issue and I'd like some exposition here in order to understand your motivation (both so I can reply and also just because I'd be fascinated simply to understand your reasoning on this in general).

There could be a readability issue here, but a priori I don't see one. In fact, my experiences with things like HyperTalk and this statement/expression issue, since there you have to say for each function which kind you are making, is that you often end up with things that are nominally intended to be expressions but that you want to use as statements. So you do "get foo()" just to make an expression into a statement, even though you plan not to use the "it" variable that "get" sets up.

I find the statement/expression distinction to be tedious and pointless as an enforced mechanism. Though in practice, again, Lisp programmers often have certain expressions they tend to think of as kind of statement-like and so tend not to embed in well-styled code. So again I don't see a problem.

• Deeply nested code and structures are confusing.

The ordinary use of block structure, and the commonplace use of separating blocks into separate functions, both practices introduced decades ago in Algol and long-practiced not only in Lisp but in most major languages seems to make the issue of deeply nested code not an issue. I'd need to see an example to know what this was about. I don't think Lisp gets a lot more nested than most other languages. Certainly nothing about the language forces this. Unless you want a language like Basic or Assembly that doesn't allow any nesting, I don't see how to avoid at least the possibility, and beyond that it's all just personal taste and personal practice, not language design. Do you see otherwise?

• Flatness is good.

You know, at MIT on a mid-term exam in compiler design 20 years ago, I actually saw a question that was "Gotos are (a) good (b) bad". I was immediately alerted to the fact that Computer Science should probably be better named Computer Religion, since it's often more filled with unfounded religious dogmatism than with science. I believe goodness and badness are things that have to be context-relative. One can't just stop a sentence after the word "good" or "bad" without establishing a context and have anything other than a statement of religion. It may be that flatness is good for some unspecified purpose, and that if you specified that purpose we could talk about it more. But I won't give you unqualified Good® on no more than you've offered here.

• Meaningful error messages help.

I have to say I don't know where this comes from. Lisp has an error system capability that is unmatched by any other language I've seen, and has the best guidelines for writing error messages that I've seen anywhere also. If you want an abstract overview of its capabilities, see my paper Exceptional Situations in Lisp . It is not possible to make a programmable facility that leaves the programmer any discretion at all and not risk that someone will do something obscure, but (again) you can't blame the language for that. As a rule, Lisp error messages, in part because they are object-oriented, and in part because of the power of Lisp's powerful FORMAT facility for producing formatted output, seem to me to be much better than I get in other languages. So I'm not sure what you're talking about here.