Hacker News new | comments | show | ask | jobs | submit login

This question sounds like it's from 2005 rather than 2010. Lisp seems to have become fashionable again now, thanks to Clojure.

I'm sure Python has very good libraries, but I would find it constraining to program in a language without proper macros.




The problem with the Blub paradox is that there's no total ordering.

I do Common Lisp and C++ at my day job (ITA), and I do much of my personal hacking in Python. In Python and C++ I miss macros; in Lisp and Python I miss RAII and strong typing; in Lisp and C++ I miss dictionary literals.

And, in all of them, I miss algebraic datatypes.


Hello, my co-worker, whoever you are. Yes, Common Lisp should have dictionary literals. I don't know why there hasn't been a commonly-used reader macro for this. (Emacs Lisp mode and other tools would have to know about it, so it needs to be a widely-accepted convention.)

Common Lisp does have strong typing. What it does not have is static typing.

I am at the SPLASH conference, and the Dynamic Language Symposium is happening right now. There is controversy over whether we can find a way to have the benefits of both static and dynamic typing in the same language. The great advances in type inference make me hopeful. The keynote speaker, Allan Wirfs-Brock, replied to my question about this with more pessimism. It is not a simple question; for one thing, not everybody even agree about which factors are "pro" or "con" for either static or dynamic. I am not doing programming languages these days (I'm doing databases) but I continue to be hopeful.


Hello, my co-worker, whoever you are.

John Stracke. (I've been staying pseudonymous, but today I mentioned Adder, which is tied to my real identity.)

Common Lisp does have strong typing.

True. I need to remember to be more precise; "doesn't have strong typing" just means "doesn't have type feature Blub". Common Lisp has runtime type safety, and type hints for efficiency; what it does not have is the pervasive typing that I'm used to from C++, which has a separate set of benefits. The most obvious is that, in C++, I can change the interface to a class and be certain that the compiler will catch any caller that uses it incorrectly. (Although I suppose it may be possible to do something like that with CLOS. I haven't used much CLOS, since ITA avoids it.)

There is controversy over whether we can find a way to have the benefits of both static and dynamic typing in the same language.

I'd say that type inference already brings us nearly there: the convenience of dynamic typing, with the rigor of static typing.

I may be wrong, though; I've used ML and Haskell, but not enough to really feel where the pain points of type inference are.


'True. I need to remember to be more precise; "doesn't have strong typing" just means "doesn't have type feature Blub". '

That might be less precise, but more correct :-P.

"Common Lisp has runtime type safety, and type hints for efficiency; what it does not have is the pervasive typing that I'm used to from C++, which has a separate set of benefits. "

The type declarations aren't just for efficiency (although they are frequently (ab)used for it).

"The most obvious is that, in C++, I can change the interface to a class and be certain that the compiler will catch any caller that uses it incorrectly."

I'm not sure what common lisp version you use, but wouldn't this be fixed by simply declaring types of everything? You can declare the types of on the slots of a struct, you can declare the types of arguments to functions, results of functions, variables, slots of objects, contents of sequences... (having trouble thinking of something you can't declare types on, maybe a hashtable? Although you could wrap the accessors in a function).

Then SBCL (at least) yells at you when you go to recompile the project.


wouldn't this be fixed by simply declaring types of everything?

Yes, but I'm not so sure about the "simply". It's only marginally easier in C++; but at least you know that haven't forgotten to declare anything.


> I haven't used much CLOS, since ITA avoids it.

Interesting. Is it for performance reasons?


...actually, I don't know. When I started, I was told we don't use it; I don't remember whether I was told a reason. If I was, it was performance; anything else would have been surprising enough to remember.


I wonder if it's similar to why Jane St doesn't make a lot of usage of the O in Ocaml (from what I've gathered at least, I don't work there.....yet). Object systems can be nice but they tend to make understanding your code all the harder since you have all the dispatching. I don't know anything about CLOS but this is pointed out as a reason against using Java and the object system in Ocaml in the Caml Trading video.


I did mention in the original essay that it was only a partial order, in footnote [4].


Ah, but metageek's point is that it's not an order at all. It contains cycles.


Sorry, I haven't read it in a while.


Forgive me, but I think you mean in python you miss static typing.

Python is strongly typed.

Also, just to jab at C/C++, pointers to void... really? It all but makes C/C++ a weakly typed language.

http://wiki.python.org/moin/Why%20is%20Python%20a%20dynamic%... http://www.artima.com/weblogs/viewpost.jsp?thread=7590 http://en.wikipedia.org/wiki/Duck_typing http://articles.sitepoint.com/article/typing-versus-dynamic-...


> in Lisp and C++ I miss dictionary literals

So roll your own. Or use mine:

http://flownet.com/ron/lisp/dictionary.lisp


I can't help you with strong typing, but I'm pretty sure a macro would go a long way towards implementing RAII in a Lisp.


> I'm pretty sure a macro would go a long way towards implementing RAII in a Lisp.

Well yeah, just build the macro you need on top of unwind-protect, that's pretty standard common lisp fare.


That's true; we've already got special cases like WITH-OPEN-FILE.


Actually, you already have something better than RAII in unwind-protect. Just create whatever macro you need on top of that (I'm pretty sure with-open-file is just a macro on top of unwind-protect, Siebel seems to agree in his chapter on files) and you're done.


Why do you miss dictionary literals? Syntax similar to arc's seems to do it for me:

  (obj a 1 b 2 c 3)


We do the same thing:

  (make :a 1 :b 2 :c 3)
which macroexpands into a plist in CL and {a:1, b:2, c:3} in JS. I've grown to like this idiom a lot. Yeah, you have to type OBJ or MAKE or whatever but in return you get something that integrates completely smoothly with the rest of the language.


Y'know, I'm not sure. Next time I need to use a hash, I'll create something like that and see how it feels.


What about Qi? What about Typed Racket?


Typed Racket combines all the inconvenience of type declarations with all the performance provided by a dynamic language.


One question I've had about Typed Racket since I first saw it: why all the colons? Seems to mess with the elegance of Lisp, and especially Scheme.

There has to be another friendlier syntax for typing, no?


why not ? colons are used to denotes values type in ML


The Python philosophy is that macros do more harm than good, making it harder for someone to read/understand your code in the long term. These and other "constraints" make the code more accessible to others and even yourself.


Macros are just another abstraction tool. If you poorly use an abstraction tool, it makes the code harder to read, if you properly use an abstraction tool, it makes the code easier to read.

Here's a function that makes code harder to read:

def sumAList(aList): return 7

This doesn't mean that functions are bad.

Now there is an argument that macros make code harder to read in that I've yet to see a really good macro system that isn't dependent on the code having very little syntax (e.g. S expressions), since the more different the code is from the AST, the harder it is to manipulate the code successfully.

Combined with the fact that more syntax can make code much easier to read, there is a conflict here.

However, I don't think that's the argument you are making.


The argument is that macros have non-local effects; they interact with the code in which they are applied. This means that the macro definition and the code surrounding the macro invocation can't necessarily be understood in isolation.

This is also essentially the argument against global variables.


A function definition is, in general, far away from the function call. If you think this problem is more severe for macros than for functions, then you should articulate why. You may well have a very valid point in your mind but I think it needs to be expressed somewhat more specifically.


For non-hygienic macros, it's essentially the variable capture problem.

For hygienic macros, I don't know of a good argument that they are inherently more difficult to understand separately from their invocation than a function.

(I'm not personally arguing against macros - or global variables for that matter - just trying to state the argument).


I think it should be obvious that you use programming constructs only when difficulty of understanding it is less than the difficulty of understanding code without it (over the whole program). This applies to functions, classes, macros, frameworks etc.

Full macros (like in CL where they are just functions that don't evaluate their arguments) give the programmer same power as compiler writer or programming language designer.

ps. To really get benefit from Lisp macros, you would need to standardize code walker. Without code walker, macros can't reach their full potential.


What is code walker?


If you want local reasoning you will have to reject Turing completeness, otherwise you could implement a language with global variables and eval a bunch of code in that language.

I think we shouldn't be limiting our tools. We should instead limit their use. Global variables can be nasty, but it's nice to have them when your code is best expressed with global variables. Same for macros.


Yes, but any given function is usually extremely easy to understand, because it's only, say one level of abstraction, then a macro is a few levels higher than that. And as you go up in your levels of abstraction, it gets harder and harder to really understand what's going on. Sure, some macros are intuitive and easy to follow, but those are usually easily replicated with other things, especially in a dynamic language like Python.

I also don't mean to imply that Lisp is lesser for using macros. I love Lisp and any implementation clearly requires macros. But Lisp is also, undeniably, harder to read for this and other reasons.


Hmmm. I think your argument is roughly that there is a "sweet-spot" for abstraction when it comes to readability?

That is a point at which less abstraction makes the code harder to read, and more abstraction makes the code harder to read?

I will agree with this in specific cases (i.e. for any given solution, there is a point at which adding abstraction can't improve readability), but I'm not certain I agree in the general case (i.e. that using macros cannot improve readability).

I guess it also depends on what you mean by "really understand what's going on." I started out programming in C. Now in C, if you know your compiler well, you can predict fairly accurately what binary code will be generated when you compile with optimizations off. Moving to higher level-languages you lose this ability, and no longer "really understand what's going on."

For systems programming, I may still use C to get this advantage. For other problem domains, I sacrifice this knowledge because representing my problem more tersely in a higher level language makes the code more readable and easier to understand. Now I will never know exactly which instructions will be executed when I write in Python.

Similarly, with sufficiently fancy macros, I may not know what LISP code is generated, but if the macros do what they say they do, it can make my code less verbose, more understandable, and easier to maintain. There are times when really understanding what is going on trumps the terseness, and those times I don't use macros.

Also, I love Python. It embeds well in C (which is where my original background is), and it has very good portability, and a good set of libraries.

I also implied, but didn't say straight out that Python has a good reason for not having macros: Part of its design is to look like pseudo-code. See also Norvig's comment to the OP. Macros that operate on text rather than trees (C preprocessor, m4, etc) are far more error prone, and probably a Bad Idea. Therefore if you want your language to look like something other than a tree, you have to forsake macros that operate on code as it is written. I have seen for several languages (Python among them I believe) Lisp-like macros that operate on the AST of the language. They have not caught on. I have several theories why this is so, but right now my preferred one is that it feels too much like you're hacking the compiler, and Compilers Are Scary.


right now my preferred one is that it feels too much like you're hacking the compiler

I think what you implied just before that is a stronger argument: it's way too distant from the base language, and this semantic distance is so costly that it's not worth the trouble.


"And as you go up in your levels of abstraction, it gets harder and harder to really understand what's going on."

There is a difference between abstraction and indirection. Just because you've added the latter doesn't mean you've gained any of the former.

"Sure, some macros are intuitive and easy to follow, but those are usually easily replicated with other things, especially in a dynamic language like Python."

How would you implement SETF in Python? Or how about compile-time link checking for a web application (http://carcaddar.blogspot.com/2008/11/compile-time-inter-app...)?


At the International Lisp Conference last year, I put in an evening event called the "Great Macro Debate", in which these issues were discussed. (We encouraged humor, and flaming as long as it was witty, so it was a lot of fun.) What you say is true to an extent. Macros, like most things, can be abused. If you have a group of Lisp programmers, one thing you can do is have the junior ones request advice from the senior ones about what constitutes "tasteful and idiomatic" use of macros, and vet particular macros, since it is rather hard to crisply "pin down" just what those things mean.


I wish there was a language called harmless which common folk could use to express common thought without any fear. It would go like this:

do this do this and that and that too do this amen

No branching nor decision trees as not to confuse common folk. Now programming is a socially acceptable activity!


Macros can be used in python.

There are a few libraries that help make it easier(so you do not need to manipulate the ast yourself). For example:

  @macro
  def macroname(arg1, arg2):
     ... macro contents ...
There's some current information for you old time lispers, so next time you don't sound so dated in your Battles with Trolls in the great never ending language war flames ;)


I like how you imply that you don't participate in the language wars. When you just did.


Link? The only "macro" library I've seen for python has been "MetaPython" (http://metapython.org/), which is more of a let down than it is useful, unfortunately.


Even if that happened to work correctly (which I don't believe), you would still be missing a bunch of macro-related stuff that makes CL the programmable programming language it is, and Python isn't:

-reader-macros

-symbol-macros

-compiler-macros

-macrolet

-symbol-macrolet

EDIT: Fixed layout


Well, those kinds of claims are kind of par for the course for the Python community. I remember that it was commonly claimed that Python 1.5 had the "full power of the lambda calculus", when all it had was anonymous function definitions, and not true higher order functions.




Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact

Search: