libera/#commonlisp - IRC Chatlog

13:55:18 nij- I'm not sure. Just thinking about the possibility ..

13:55:40 nij- phoe: By process you mean a lisp process?

13:55:50 phoe yes

13:56:06 phoe a standalone, executing lisp image

13:56:14 hayley With only one machine, it is perfectly fine to use mere threads, which share an address space, and thus you can literally just give a thread the object in question.

13:57:38 nij- I see, phoe, and one working implementation is swank-crew right? I will look into it :)

13:58:39 hayley If the work is trivial to parallelize, then I would look into lparallel and toy with PMAP, PREDUCE, PREMOVE-IF-NOT, etc. If not, then you might want to brush up on parallelism before anything.

13:59:14 nij- Back to compiler. beach, do you recommend noobs like me to start with understanding how C codes are compiled into assembly? Or can I just try to understand how it's done for CL? I have much more patient for CL than for C.

13:59:25 hayley Maybe I should write another chess AI some day. My first and last one nearly worked, but I messed up the negamax thing and it ended up playing the worst move half the time.

13:59:33 nij- hayley: thanks for the keywords too!

13:59:52 lisp123 hayley: Are you working on rule based AI?

14:00:38 phoe nij-: yes, swank-crew builds over swank-client which is an implementation of swank protocol in CL.

14:01:03 hayley lisp123: No, a chess program does state space search.

14:02:28 lisp123 hayley: Nice!

14:02:46 hayley But I haven't written one for years.

14:02:48 beach nij-: OK, there are (at least) two aspects to a compiler. One is translating the source language to intermediate form. The other is optimizing the intermediate form.

14:03:34 beach nij-: The first part is specific for each language of course.

14:03:49 phoe and for this particular issue you're more interested in the second aspect

14:03:59 hayley Seriously, I remember messing with threading in...2018 while I was waiting for a meeting to pick classes for my final year at high school.

14:04:05 beach nij-: You can do that for Common Lisp if you want, there are several ways.

14:04:25 beach nij-: And, as phoe points out, for the points about OR and LET, the second part is more interesting.

14:04:31 phoe stuff like narrowing variable lifetimes, figuring out constants, eliminating dead code, etc..

14:04:36 beach nij-: And then the source language doesn't matter much.

14:04:44 phoe a good thing is that this is mostly language-indepe--exactly what beach said

14:05:41 beach nij-: I recommend Steven Muchnick's book for that.

14:06:33 beach nij-: That book is a good overview of techniques, and the general descriptions are good. But if you ever want to write a compiler, whatever you do, don't base it on his code.

14:06:59 shka beach: that bad or just overly complicated?

14:07:01 nij- The intermediate lang is almost universal?

14:07:17 shka or just overly simplistic

14:07:21 beach shka: Very bad. The man wrote a compiler, but he doesn't know about pointers.

14:07:42 beach shka: It is as if he wrote the compiler in Fortran.

14:07:45 shka that is... interesting

14:08:24 Josh_2 casual 800+ pages

14:08:26 beach nij-: All books assume a simple source language like C without closures and stuff, so languages like Common Lisp complicate stuff, but you still get the general idea from his book.

14:08:27 shka moment

14:08:44 hayley nij-: I think that the parts an application programmer needs to know about are relatively language independent, at least if you have a reasonable language. Otherwise hell no.

14:08:52 shka old version of fortran lacked what compiler people call "pointer aliasing" right?

14:09:05 beach nij-: I second what hayley says.

14:09:08 nij- You mean the ~900-page book 😂😂😂?

14:09:18 shka could this is be why code uses pointers in weird fashion?

14:09:56 beach shka: I am talking about his data structures. They are all arrays indexed by integers.

14:10:25 beach shka: Exactly the way you would write a compiler if all you know is Fortran.

14:11:16 Josh_2 nij-: fortunately its mostly code

14:11:17 shka it honestly astonish me that anybody would try to teach anything non-numeric with Fortran of all things

14:11:20 hayley Well, to some extent, you do also have different intermediate languages and representations (words you don't need to care about: SSA, CPS, ANF, basic blocks, sea of nodes...) but I guess the optimisations are invariant still.

14:11:24 shka but ok, i guess

14:12:36 beach hayley: Yes, I agree.

14:13:09 shka the book was first published in the 1997?!?!?!?!

14:13:15 shka and Fortran?

14:13:18 _death the fortran style has its own advantages sometimes, though in Lisp we tend to use (maybe overuse) the pointers approach a lot.. you can read about it in http://www.the-adam.com/adam/rantrave/st02.pdf

14:13:46 hayley nij-: I would guess a book would not cover the specific IR of some real compiler, so you are welcome to imagine your own IR to think about optimisations with.

14:13:54 beach shka: The man just doesn't know how to program.

14:14:36 shka beach: i would not dare say such thing, i mean he somehow became very well acquainted with compilers

14:14:44 shka but this is just so weird

14:14:53 beach Very strange indeed.

14:15:29 beach But then, I hear there are people using languages such as C++ to write compiler frameworks such as LLVM. That's weird too.

14:17:50 shka yeah, C++ is not the best choice, but again given the selection of the mainstream languages and corporate politics it is understandable

14:18:33 shka you wanna automatic management? C# or java, both of which are very much connected to MS and Oracle respectively.

14:18:48 shka and neither is exactly a "stable standard"

14:19:27 beach Like I often say, people go to a lot of trouble, and waste a lot of time and energy, to avoid learning Common Lisp.

14:19:41 shka true

14:20:52 Josh_2 very true

14:21:06 hayley According to Wikipedia, LLVM originated as a project to investigate dynamic compilation techniques. With the exception of KleinVM for Self, I don't think there were any "just in time" compilers not written in C++ at the time.

14:22:07 shka hayley: i don't think that "exists only in C++" is a valid excuse

14:23:24 pl I think Python would count too, even if arguably it uses older logical framework than LLVM

14:24:08 hayley Ironically now it seems LLVM is too slow to use for a JIT, with the exception of optimizing the hottest loops.

14:25:55 hayley shka: What I mean is that metacircular dynamic compilers were mostly non existent. But as pl said, Python the compiler did exist then.

14:27:16 beach hayley: I have been wondering whether the slowness of LLVM is due to this phenomenon that I often cite, namely that it is impossible to write a C++ program that is both fast and modular.

14:27:23 scymtym beach: Aaron Hsu's thesis has a more well-founded position on avoiding pointers in compilers than "only knowing fortran": https://scholarworks.iu.edu/dspace/handle/2022/24749 . i'm not sure whether it contains his statement about pointers being "the refined sugar of programming", though

14:27:48 beach I mean, I can't imagine that the LLVM people attempted to write a monolithic program of that size.

14:28:56 beach scymtym: I see, yes. I don't think that's what Muchnick is up to though.

14:29:43 beach hayley: But I haven't studied the LLVM code to see whether they make heavy use of things like smart pointers and/or reference counting.

14:30:04 scymtym beach: very likely true. i was pointing out (ha) other possible reasons for wanting to avoid pointers

14:30:21 beach scymtym: Yes, thank you!

14:32:03 beach ... smart pointers, reference counting, or perhaps just a lot of copying to keep the reference count to 1 or 0.

14:32:29 beach Either "technique" could explain a lot of slowness.

14:36:24 hayley I don't know what the LLVM developers do, but I watched a presentation on the Java C2 compiler, in which Cliff said he did a lot of hash consing in order to keep everything in cache.

14:37:24 shka compilers are that cache performance sensitive?

14:37:42 hayley And in the context of a compiler, you could be slack and use an arena allocator, assuming no IR or other temporary data outlives compilation.

14:38:07 hayley shka: Apparently so. But I suppose going slow hurts more in a JIT compiler.

14:38:21 shka i would never thing so

14:38:27 shka *think

14:39:50 beach Didn't GCC used to use obstack and then switched to Boehm or something like that?

14:40:47 hayley I believe so.

14:45:34 hayley C2 apparently uses an arena allocator, and so does the frontend of Clang.

14:46:45 beach But that gives more responsibility to the programmer to determine liveness.

14:46:59 hayley So garbage collection could be somewhat better on the cache, provided that there are temporary objects which die.

14:47:37 beach So it's an unwanted source of the same kinds of bugs that manual memory management has. Right?

14:47:55 hayley But if the compiler doesn't run for long, and nothing outlives compilation, the programmer can be lazy and remove the arena at the end of compilation.

14:48:19 beach Maybe so.

14:50:48 hayley Still, you could achieve much better locality of reference if there is any garbage produced. And for sufficiently large compilation units, the memory usage would become a problem, so I doubt that LLVM solely uses arenas.

14:51:23 beach Sounds right.

14:51:48 hayley ACTION imagines this isn't far off how an explicit memory management fan would talk about a program with a GC.

14:51:49 shka maybe allocates multiple chunks

14:53:03 hayley Maybe, but any chunks would only be provably dead when compilation finishes.

14:54:08 shka hmmm

14:54:31 hayley If there were cleanly separated passes, you could have separate allocators for each pass.

14:54:41 shka yeah, wanna suggested that

14:54:49 hayley Still, I expect there to be some other memory management technique.

14:54:51 shka *yeah, i wanted suggest that

14:55:15 shka honestly, memory management is not all that interesting :/

14:55:23 shka it is like tetris

14:55:28 shka for programmers

14:56:29 hayley It's boring stuff that makes the rest of my life boring. 10/10 would study again

14:56:31 beach I am always in favor of general-purpose techniques rather than special-purpose ones. So it seems to me work should be put into a good tracing GC.

14:58:37 hayley shka: w.r.t the cache, I think the example of hash consing was for type inference. As that compiler also does something like Kildall's algorithm, it also makes a fair few intermediate types, and getting that done with quickly would be good.

15:20:14 nij- Ah - the link to the internal manual for sbcl in this site is down - http://www.sbcl.org/manual/#Internals-Documentation

15:20:22 nij- Does anyone have a copy of the internal manual?

15:21:53 nij- Btw, as wscl is going on - can we expect a program that checks if an implementation satisfies spec wscl?

15:22:52 beach Augmenting the ANSI test suite would be a good thing.

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19:16:50 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:16:52 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:16:54 moon-child 7?

19:16:54 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:16:56 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:16:58 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:17:00 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:17:02 mfiano 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

19:17:04 mfiano 77777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777788888888888888888888888888888888788888888888666666666666666666666666666666666666

19:18:10 lotuseater oh hm something went wrong :)

19:19:46 _death I expect the culprit has paws

19:30:25 shka i did this once because i was cleaning keyboard

19:30:32 shka and i forgot to unplug the thing

19:33:13 mfiano Wow, sorry. Guess this keyboard is dead if it's doing things without me

19:47:47 edgar-rft on the contrary: your keyboard is alive - it's taking over your computer now!

20:21:27 Josh_2 if I have a list with 100 different elements, each element has a slot whose value is a colour like orange, green, blue, is there a quick way I can sort them into individual lists by that colour?

20:24:24 lisp123 Josh_2: So to understand correctly, you have a list, say (A B C D E F G), and you want to split it into (A B) (D F) (E) (G) where each of the sublists are of a certain color?

20:24:55 Josh_2 yes, I can do this by looping, was just curious if there is a quick way to do this

20:24:56 phoe oh goodness

20:25:03 phoe that is a really big integer

20:25:18 Josh_2 sometimes there are sneaky ways you can do this in CL without realizing, no point reinventing the wheel

20:25:39 phoe Josh_2: I remember that pjb had a utility for that

20:25:55 Bike you're describing a partition

20:26:04 lisp123 http://www.lispworks.com/documentation/HyperSpec/Body/f_mem_m.htm - then use a lambda function to test for equality

20:26:14 Bike there's nothing for it in the standard, but some utility libraries have it, i'm sure

20:26:57 lisp123 I'm sure you could use a mapping function also

20:27:01 Bike not alexandria though as far as i can tell

20:27:38 phoe serapeum:partition

20:28:02 zephyr i've also seen that called group-by

20:28:05 phoe sorry, serapeum:partitions

20:28:35 phoe (serapeum:partitions (list (lambda (x) (= 0 (mod x 3))) (lambda (x) (= 1 (mod x 3))) (lambda (x) (= 2 (mod x 3)))) '(1 2 3 4 5 6 7 8 9))

20:28:43 phoe ;=> ((3 6 9) (1 4 7) (2 5 8))

20:28:57 Josh_2 hmm

20:29:21 Bike hm, well that's slightly more involved

20:30:40 phoe only because the predicates are there

20:30:47 phoe you can generate them on the fly via closing over your colors

20:31:10 lisp123 https://stackoverflow.com/questions/36634561/common-lisp-idiom-for-filtering-a-list-and-applying-a-function-to-the-unfiltered

20:31:13 phoe something that can turn '(:green :red :blue) into a list of lambdas that check if the color of an object is :green, :red, :blue

20:31:47 pjb phoe: (com.informatimago.common-lisp.cesarum.list:equivalence-classes '(1 2 3 4 5 6 7 8 9) :key (lambda (n) (mod n 3))) #| --> ((9 6 3) (8 5 2) (7 4 1)) |#

20:31:59 Bike sure, but maybe you don't know the colors to begin with

20:32:05 phoe pjb: exactly this

20:32:05 phoe thanks

20:32:43 lisp123 Bike: (which is probably likely) - I guess then the trick would be to CDR through the list and push to a hash table for that color?

20:33:09 Josh_2 the colours are unknown in this case

20:34:04 lisp123 Josh_2: see above, loop through the items, and push each object onto a hash table with that color as a key (appending to the list for each color as you go on)

20:34:46 Bike https://github.com/informatimago/lisp/blob/master/common-lisp/cesarum/list.lisp#L651-L665 which is more or less how pjb's function works.

20:34:58 jcowan That's when autovivification would be a great thing to have

20:34:58 pjb (defmacro generate-keyword-predicates (&rest keywords) `(progn ,@(mapcar (lambda (keyword) `(defun ,(intern (concatenate 'string (string keyword) "P")) (object) (eql object ',keyword))) keywords))) (macroexpand-1 '(generate-keyword-predicates :red :green :blue)) #| --> (progn (defun redp (object) (eql object ':red)) (defun greenp (object) (eql object ':green)) (defun bluep (object) (eql object ':blue))) ; t |#

20:35:20 Bike well there's a two dollar word

20:35:30 pjb Josh_2: if the colors are not known at compilation-time, then you don't want to generate functions for each of them.

20:35:33 lisp123 Bike: yay, i'm beocmign smarter

20:35:40 lisp123 guessed it right :D

20:35:50 Bike "the automatic creation of new arrays and hashes as required every time an undefined value is dereferenced" eck

20:35:56 pjb Josh_2: no code compiled can know what those function names would be if the color keywords are only known at run-time.

20:37:44 phoe but you can close over them at runtime

20:38:08 phoe (mapcar (lambda (color) (lambda (x) (eq x color))) colors)

20:38:19 phoe this gives you a list of predicate objects that you can freely funcall

20:38:50 Josh_2 got some more complicated answers than I expected

20:38:53 Josh_2 heres my bad solution

20:39:12 Josh_2 https://plaster.tymoon.eu/view/2585#2585

20:41:19 Josh_2 I can easily display this as a table in HTML

20:41:24 Josh_2 Thanks for the suggestions :D

20:43:52 zephyr i'll throw in https://plaster.tymoon.eu/view/2586#2586, looks similar to other suggestions

20:46:10 pjb phoe: this is correct, but more often it will be enough to use (member x colors).

20:46:20 pjb or (position x color)

20:46:25 pjb or (position x colors)

20:46:37 phoe oh right, sure

20:46:38 pjb (it'd be better to have some specifications).

21:37:56 Bike sm2n: i just loaded introspect-environment on sbcl 2.1.7 and don't see any errors. there is a compiler note but i am pretty sure it is harmless.