A "declare" form returned by macro

Discussion of Common Lisp

Re: A "declare" form returned by macro

Postby findinglisp » Tue Jan 06, 2009 10:18 am

Paul Donnelly wrote:
findinglisp wrote:In addition to all the other fine suggestions about how you can ease your pain in declaring types, might I suggest that you simply don't declare types at all.

Amen to that. Most of the time, type declarations are pointless.


Yes. Type declarations are a silver bullet that you should pull out once you have profiled your code and determined where your inner loops are and you're going off to optimize things. Until then, they're just needless baggage. Further, you can actually shoot yourself in the foot if you start changing types during development and need to go back and get all your type declarations to match. If you miss something and your SAFETY settings are low, you can actually have a program that doesn't work.

So, even if you're a Lisp guru, I'd still recommend that you (1) write your code, (2) test your code, (3) profile your code, (4) THEN optimize your code, possibly with type declarations if necessary (better yet choose better algorithms), and finally (5) retest your code to make sure you didn't bork anything when you were optimizing.

If you're a Lisp newbie, simply ignore typing altogether. Lisp is not C.
Cheers, Dave
Slowly but surely the world is finding Lisp. http://www.findinglisp.com/blog/
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Re: A "declare" form returned by macro

Postby TPJ » Fri Jan 16, 2009 4:32 am

Thank you all for your tips.

findinglisp wrote:In addition to all the other fine suggestions about how you can ease your pain in declaring types, might I suggest that you simply don't declare types at all. If you're really trying to write your first code in Common Lisp, the last thing you'll want to spend any time on is typing. Lisp doesn't require typing, so why use it? Yes, yes, I know performance, blah, blah. But come on. This is your first code. Figure out the language. Get it to run. Then worry about whether it's running fast enough. Trust me, if this really is your first program in CL, you'll be consing so much as to make all your type declarations all but irrelevant anyway.


I really don't want to start (yet another) rant on the "dynamic vs. static typing" here, so I'll just point my point of view.

I'm coming from static typing world (mainly Java). Although type hints *might* (not: *will*) improve performance, in my opinion they make code more readable. When I say:

Code: Select all
(defun my-fun (a)
  (declare (type fixnum a))
   ...)


I'm making it clear that "a" is a fixnum number (and not a string, a list, or something else).

My experience from using both static (mainly Java) and dynamic (mainly Python) languages shows, that using such a type hints (let's treat them as hints) allows to write less error-prone and more readable code (at least for me).

That's the main reason why I'm trying to use type hints in CL.
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Re: A "declare" form returned by macro

Postby Ramarren » Fri Jan 16, 2009 5:13 am

In my opinion, if it is not clear on a glance what arguments the function accepts, then it is either too long or the arguments are badly named. At least for simple types, and more complex things are best put into CLOS objects and operated upon with generic functions, which have something quite close to type signatures. Anyway, if the type hints are primarily for human consumption, I think they should be in a docstring, where SLIME or (describe ...) can find them, rather than in declarations which might be thrown out by some compilers (CLISP I believe ignores all type declarations, or at least it did few years ago).
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Re: A "declare" form returned by macro

Postby Paul Donnelly » Fri Jan 16, 2009 10:51 am

TPJ wrote:
Code: Select all
(defun my-fun (a)
  (declare (type fixnum a))
   ...)

This just makes me wonder why it wants a fixnum specifically.
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Re: A "declare" form returned by macro

Postby blandest » Fri Jan 16, 2009 2:46 pm

Ramarren wrote:In my opinion, if it is not clear on a glance what arguments the function accepts, then it is either too long or the arguments are badly named. At least for simple types, and more complex things are best put into CLOS objects and operated upon with generic functions, which have something quite close to type signatures. Anyway, if the type hints are primarily for human consumption, I think they should be in a docstring, where SLIME or (describe ...) can find them, rather than in declarations which might be thrown out by some compilers (CLISP I believe ignores all type declarations, or at least it did few years ago).


When you use packages and suggestive names for functions and variables, the whole Java world begins to look like this: http://paulgoscicki.com/pictures/static-typing.gif :)
Of course, some languages have very good type inference and look smarter than the above example but I still believe in documentation (describing functionality, not just classes and functions) so maybe I'm loosing modern Java IDE features because of my ignorance ...
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Re: A "declare" form returned by macro

Postby findinglisp » Fri Jan 16, 2009 3:25 pm

TPJ wrote:I really don't want to start (yet another) rant on the "dynamic vs. static typing" here, so I'll just point my point of view.

I'm coming from static typing world (mainly Java). Although type hints *might* (not: *will*) improve performance, in my opinion they make code more readable.


I respect that you find it more readable. If you do, that's fine. Many others won't, however. Idiomatic Lisp code doesn't use lots of typing. Writing Lisp as it it were Java does not result in readable code for native Lisp speakers. It's like trying to speak a foreign language and deliberately using your native accent or grammar constructions when you pronounce the foreign words. It just pisses off the native speakers of that language. If you're going to speak a foreign language, at least try to use the correct accent and grammar. Yes, you won't get it down immediately. That's understandable. But it will come over time and people will have more respect for you if they see you trying. Put simply, if you want to sit in your own room and talk French to yourself with a Russian accent, that's fine with everybody because nobody has to hear you, but don't expect the French to think you're doing it right.

Regarding performance, in many cases, the compiler can infer types in any case (see what SBCL does, for instance, and you'll be amazed. It's not perfect, but unless you're in an inner loop, I'm sure you'll find the compiler type inferencing more than enough for your needs. Again, particularly as a newbie.

When I say:

Code: Select all
(defun my-fun (a)
  (declare (type fixnum a))
   ...)


I'm making it clear that "a" is a fixnum number (and not a string, a list, or something else).


Except now my-fun doesn't work (assuming you have a high enough SPEED optimization setting for the compiler to listen to you) with bignums. Or floats. Or any other numeric type. Instead, I would suggest:
Code: Select all
(defun my-fun (num)
     ...)


Use "lst" or "l" for lists, "arr" for arrays, and "seq" for general sequences, for instance. There is no standard for this sort of thing, but there are several conventions and people will immediately understand it.

My experience from using both static (mainly Java) and dynamic (mainly Python) languages shows, that using such a type hints (let's treat them as hints) allows to write less error-prone and more readable code (at least for me).

That's the main reason why I'm trying to use type hints in CL.


Okay, that's fine. You can do whatever you want. I won't argue with you further. Just realize that anybody else who knows Lisp will look at your code and say "Gak!" :shock:
Cheers, Dave
Slowly but surely the world is finding Lisp. http://www.findinglisp.com/blog/
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Re: A "declare" form returned by macro

Postby Paul Donnelly » Fri Jan 16, 2009 5:24 pm

findinglisp wrote:Use "lst" or "l" for lists, "arr" for arrays, and "seq" for general sequences, for instance. There is no standard for this sort of thing, but there are several conventions and people will immediately understand it.

If you're feeling really explicit, you could even type the whole word out. :o
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Re: A "declare" form returned by macro

Postby Exolon » Fri Jan 16, 2009 5:52 pm

blandest wrote:When you use packages and suggestive names for functions and variables, the whole Java world begins to look like this: http://paulgoscicki.com/pictures/static-typing.gif :)

I have to say that Common Lisp's package management feels quite cumbersome for a newbie (or maybe the tutorial I picked back then just introduced it in an overly-verbose way, creating at least two superfluous files just to define the package and asdf systems it relied on).
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Re: A "declare" form returned by macro

Postby Paul Donnelly » Fri Jan 16, 2009 8:18 pm

Exolon wrote:
blandest wrote:When you use packages and suggestive names for functions and variables, the whole Java world begins to look like this: http://paulgoscicki.com/pictures/static-typing.gif :)

I have to say that Common Lisp's package management feels quite cumbersome for a newbie (or maybe the tutorial I picked back then just introduced it in an overly-verbose way, creating at least two superfluous files just to define the package and asdf systems it relied on).

ASDF systems aren't related to packages. ASDF is a way to load Lisp programs and libraries, while packages are namespaces for symbols. And you can put your DEFPACKAGE form in a file with some other stuff if you like. It's just helpful to put it in a separate file so that you can tell ASDF to load it first. If you're not using ASDF or multiple files, there's no reason to make a package file. ASDF is pretty clunky though.
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Re: A "declare" form returned by macro

Postby makia » Sat Jan 17, 2009 5:01 am

i really like sbcl "declarations are assertions" principle, it does helps sometimes, specially for interface (it's ugly writing assert everywhere)
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