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18:46:10
warweasle
rumbler31: They didn't want to take time to make it. Programmer's will just have to walk to the lab.
20:25:32
Xach
Does anyone here have a project in quicklisp and want to monitor its build failures through RSS?
20:32:59
specbot
Additional Constraints on Externalizable Objects: http://www.lispworks.com/reference/HyperSpec/Body/03_bdd.htm
20:34:55
pjb
jasom: I guess you could write a make-load-form for hash-table. Also, the keys and values would have to be externalizable.
20:37:08
jasom
pjb: well if ABCL allows defining make-load-form and all other implementations don't need make-load-form, I have a workable solution
20:42:03
jasom
pjb: actually in this case load-time-value is the exact opposite of what I want. I want it to be evaluated at compile time, not at run-time.
20:42:11
pjb
megachombas: also, you may want to finish output with a newline, and to flush the buffer with a call to (finish-output).
20:43:22
pjb
Notice that hash-tables have attributes that are not always visible, such as :size, :rehash-threashold, etc.
20:43:46
megachombas
actually i want to know what is passed as param in a fuction, to be able to copy this parameter and load that fuction by hand
20:45:24
pjb
megachombas: the advantage of print is that it returns its first argument so you can use it in expressions: (if (print (= (print a) (print b))) (print 'same))
20:46:01
pjb
The inconvenient is that it only prints the argument, so if you have a lot of them it may be confusing.
20:47:14
pjb
I have a macro (com.informatimago.common-lisp.interactive.interactive:show expression) that prints expression = value and returns value so it can be used as print, but its output is clearer.
20:53:45
pjb
megachombas: in C, would you write: print(list a,b,c) or print(list(a,b,c))? Would you forget the inner set of parentheses?
20:59:27
pjb
megachombas: Call the function list with as arguments 'foo a b and c is written ( =call list 'foo a b c )=end of arguments.
20:59:56
pjb
call print with as arguments (list 'foo a b c) is written (print (list 'foo a b c)) not (print list 'foo a b c)!
21:02:22
pjb
clisp contains a good tutorial: https://sourceforge.net/p/clisp/clisp/ci/default/tree/doc/LISP-tutorial.txt
21:08:40
jasom
Consider the output of this form with *print-circle* set to t and nil: (let ((x (gensym))) (list x x))
21:13:33
jasom
whatever you are interacting with is generating output that includes uninterned symbols. These are confusing if you are new to lisp, so just enable *print-circle* for now if you want to be able to paste the output and have it read in correctly.
21:18:34
jasom
megachombas: just set it to true at the toplevel before you run whatever it is that prints stuff out.
21:23:59
TMA
megachombas: the difference is that in the (let ((*print-circle* t)) (print (list 'load-machine vm asm)))) version you do not set the variable permanently, you change the value just for the print inside
21:28:17
jasom
megachombas: okay, in C, will the following expressin be true or false: "foo" == "foo"
21:29:05
jasom
megachombas: not necessarily; the compiler could in theory generate two different string literals and then it would be false because they would have different addresses
21:29:28
TMA
megachombas: not necessarily. the standard permits it to be true, but does not mandate it
21:32:20
jasom
right, when you read this in lisp, it will always generate an identical symbol named "FOO" in whatever the current package is. No matter how many times you read it, only one symbol will be created: 'foo
21:33:17
jasom
however, if you put #:foo it creates a new symbol with no package whatsoever. Since there is no package when you get another #:foo it creates another symbol with the same name, so you have two different symbols
21:34:32
jasom
now the reader has a specail tool that lets you drop objects that have already been read into the same place. You mark an object you want to include later With #N= (where N is a number) and then anywher thereafter you can put #N# and it drops the identical object there
21:35:59
Xach
Shinmera: I restructured things a little for the rss feeds. There's now http://report.quicklisp.org/feeds/author/Shinmera.rss as well as http://report.quicklisp.org/feeds/project/chirp.rss (for example)
21:36:20
Xach
they include some of the log (the part immediately before and after the start of the backtrace)
21:43:34
Xach
megachombas: the important distinction between internal and external representation is at play here
21:44:14
megachombas
because my objective is eliminate the function that generate that list, and directly read that list from a file
21:55:28
Shinmera
Well you're probably getting mad because you jumped right into the icey water and are now confused why it's so cold, instead of easing yourself in slowly.
21:56:14
Shinmera
Everything is difficult if you try to accomplish a non-trivial task in an unfamiliar environment.
21:57:02
megachombas
'Everything is difficult if you try to accomplish a non-trivial task in an unfamiliar environment.' definition of the fresh university system
22:05:57
TMA
if you do that, the |finTest7794| will be a symbol in the current package, which means (as jasom has written here already (22:32 < jasom> right, when... and following messages)) that you will probably not need the #4= (as every |finTest7794| will be read equal to other |finTest7794|) [[I am simplifying greatly, you could make it so that it will no longer true, but it would require additional effort to change it]]]
22:09:37
pjb
megachombas: you have to distinguish the textual representation from the actual data structures.
22:12:36
megachombas
so if i so (read ((move r0 r1)(move r2 r3))) that will transform it into the correct list
22:12:57
pjb
megachombas: now, the thing is that symbols are usually interned. Which means that when the same symbol name is read twice, the same and unique symbol is obtained. So there's no need for ## and #= when you read sexps containing multiple occurences of the same symbol: (a a a) is a list with 3 cons cells, each pointing from their car to the same symbol named "A".
22:13:14
pjb
(read-from-string "((move r0 r1)(move r2 r3))") #| --> ((move r0 r1) (move r2 r3)) ; 26 |#
22:14:32
TMA
megachombas: could you show me the piece od code that constructs the (@ #:|finTest7794|)? is it a code you have written?
22:14:41
pjb
Notice that the REPL uses PRINT to do the inverse transform, from lisp data structure to textual representation, so when you read ((move r0 r1)(move r2 r3)) at the repl, it prints it, and you get back ((MOVE R0 R1) (MOVE R2 R3)) ; notice the space inserted in the normalized representation! And the uppercase, if you don't have (setf *print-case* :downcase).
22:15:22
pjb
#: prevents interning the symbol, so #= ## are needed if you have several occurences of a uninterned symbol in the sexp.
22:15:45
megachombas
TMA: https://github.com/thibaudcolas/clisp-compiler-vm/blob/master/compilateur/cas/conditions.lisp
22:16:05
pjb
megachombas: you can use gentemp instead of gensym to generate interned temporary symbols so you don't have this problem with the textual representation.
22:17:52
pjb
https://github.com/thibaudcolas/clisp-compiler-vm/blob/master/compilateur/cas/conditions.lisp
22:21:15
megachombas
i will only present VM tomorrow, as i cant even explain everything that it does, as for example i dont understant what (MOVE (LOC -1 0) (:R0)
22:21:46
TMA
megachombas: the compiler uses gensym. therefore the compiler result contains the result of the gensym evaluation
22:22:53
TMA
megachombas: if the gensym was replaced by gentemp there, the compiler result will have no #: when printed and you would have no problem with it
22:23:34
pjb
megachombas: no, in lisp we never use plaintext. Instead we use lisp objects, data structures, what we call SYMBOLIC EXPRESSIONS, sexps.
22:24:35
pjb
megachombas: when you use plaintext, you get code injection problems, and you need tons of PhD theses to find complex solutions and round abouts to avoid them. ANd you get a whole cottage industry to develop tools to test and avoid them.
22:24:55
pjb
megachombas: instead, you can use 60 years old technology called lisp, which uses data structures, and therefore the problem doesn't exist in the first place.
22:26:08
pjb
megachombas: when you use a language like C, you get buffer overflow, memory leaks etc, and you need tons of PhD theses about program verifications, sophisticated debugging tools such valgrind, and a whole cottage industry of tools and security audits to detect those problems and avoid them.
22:26:41
pjb
megachombas: instead, you can use 60 years old technology called lisp, which uses a garbage collector and run-time cheks, and therefore the problem doesn't exist in the first place.
22:28:15
pjb
megachombas: just to say, that it's worth learning it, to avoid all the dumb mistake the industry keeps doing over and over.
22:29:32
pjb
(defun |()| (\(\)) (if (null |()|) () (|()| (cdr |()|)))) (|()| '(\(\) |()| (\(\)) |()|)) #| --> nil |#
22:29:35
nirved
todays computer programs are so bloated, that the equivalent lisp machine running on the same hardware would be faster
22:34:15
aeth
With Lisp you can get self-documenting function names, e.g. (defun |Hello, world!| () (format t "Hello, world!~%"))
22:41:57
Shinmera
restarts aren't the magic part, you can get them with exceptions too. The magic juice is handler-bind.
22:42:28
dim
as in e.g. https://github.com/dimitri/pgloader/commit/25152f605495fbd3e3bdae555f8ca142490a6d65 ;-)
22:44:23
pjb
megachombas: perhaps it's too late for you, and you should go to sleep? WHen you have a function name read-from-STRING, why do you pass it a list?
22:44:53
pjb
megachombas: also we've explained that reading operations consist into transforming a TEXTUAL representation into lisp data.
22:44:58
rumbler31
I think he was planning on passing it the original form with the #1= reader macros
22:45:11
pjb
megachombas: so both on the count of READ and of -FROM-STRING you should give it a STRING, and not a list!
22:46:13
pjb
megachombas: but I'm trying to activate processes in your brains so you don't have to try twice before finding the right solution!
22:49:12
megachombas
pjb: it has been around 6 damn hours im trying to figure out what does the (move (loc -1 0) :R0)
22:49:46
megachombas
the loc is generated by the compiler here : https://github.com/thibaudcolas/clisp-compiler-vm/blob/master/compilateur/cas/fonctions.lisp
22:54:21
pjb
When it's positive, it skips the return address and stack frame, to get at the parameters.
22:54:50
pjb
How the parameters are passed, and what is pushed on the stack in addition to them and the return PC.
22:55:16
pjb
Usually, there's a FP link saved on the stack. You seem to have two more slots since it adds 4.
22:55:39
pjb
This is probably described in the documentation/specification of the VM and/or the compiler.
23:05:38
aeth
It doesn't look like particularly well-written Lisp in the first place. Unless the style got messed up in the cut and paste.
23:06:09
aeth
It violates every style guide I know of, which makes it harder to read that it should be.
23:08:54
Shinmera
I've seen enough mind boggingly awful template code from university lectures that I'm entirely ready to believe someone wrote this who just doesn't know lisp either.
23:09:41
megachombas
tried to wrote my own. but at arrrived at a point where i didnt understand lisp at all. found this one that was functional, so i tried to understand it to do mine
23:10:06
megachombas
but i arrived at a point where im still trying to understand this one, and bassicly doing small modifications
23:10:33
aeth
megachombas: If you need to pick up functional Lisp-style programming in a short amount of time, work through The Little Schemer (formerly The Little Lisper). It's in Scheme, but most of the lessons would carry over imo.
23:12:10
aeth
Do not put assignments off to the last minute. I tried doing this in college, and it ruined my health, possibly permanently.
23:12:42
|3b|
ACTION just put things off until past the last minute, much better for health (bad for grades though)
23:13:09
aeth
|3b|: If there are grace periods, and you're good enough to consistently be able to get an A even with the -10% penalty or whatever, it can still work
23:13:29
Shinmera
I try to do things as early as possible, but then I just get stressed out to all hell towards the end anyway.
23:14:02
megachombas
found this http://www.lirmm.fr/~lafourcade/ML-enseign/Compilation/compil-GenCode.HTML
23:15:38
aeth
megachombas: My recommendation to you would be to pick up processing things with cond. It's fast enough that you could pick it up quickly enough. A lot of functional-style Scheme and Lisp uses that basic style. (There's no time for fancier techniques.)
23:16:36
megachombas
yes, just i discovered those instructions today ,and he NEVER EVER give it to us
23:20:11
aeth
megachombas: COND is basically an if/elseif/elseif/.../else block, except that it is a form that also returns values so you can use it just like a very elaborate ternary operator if you wanted
23:20:21
aeth
This is its documentation: http://www.lispworks.com/documentation/HyperSpec/Body/m_cond.htm
23:21:10
aeth
megachombas: You should make sure you understand COND first, because you're probably going to need it in your program if is going to have any elaborate conditionals in it. It's simpler than fancier alternatives.
23:26:13
aeth
I would personally try to build something useful from the very simple basics of Lisp rather than trying to dissect an existing Lisp program. Build up from a toy program and gradually add the features you need.
23:27:08
aeth
It's very important, at least the way I program, to have a completely working program at every step of the way.
23:27:57
aeth
If your teacher actually didn't explain things properly, then don't panic. If it's a large class, lots of people will probably do worse than you, and the grades might be adjusted upward.
23:30:31
pjb
(get-newFP 2) returns the frame pointer of the caller of the caller of the current function.
23:30:59
pjb
This is why there's this loop and it updates the LOCAL variable newFP. But it doesn't modify (get vm :FP) the actual frame pointer!
23:31:06
aeth
megachombas: Is the assignment to build a register machine like on the website you linked to?
23:33:23
aeth
Well, if there's more freedom of choice, then choose a stack machine. They're (afaik) simpler, especially in languages that have stacks (CL has two built-in stacks). That might not be an option, though.
23:39:20
pjb
(get-loc-src vm expr) reads the memory containing the value of the local variable number EXPR in the current frame.
23:39:59
aeth
megachombas: Is the assignment something like this? Given the instructions, do the operations.
23:41:14
megachombas
the asignment is 'make a VM in lisp that use 4 registerys and a lisp compiler "
23:50:36
aeth
(And if your requirement is to compile a standard Lisp or Scheme, then you're doomed.)
23:58:32
aeth
I'm not sure any Lisp resources will be helpful. The assignment itself, even to those who know Lisp, will probably take more than one day to write.
0:01:05
aeth
(And no one is going to do your homework for you, so you'd have to add the time it would take to learn Lisp.)
0:03:05
pjb
aeth: for a student, yes. I would do it in a day, I already done it several times, including an assembler, a disassembler, etc.
0:03:33
aeth
pjb: I would estimate 3 days for someone doing it the first time, student or not. Obviously doing something more than once makes you write it a lot faster. Sorry, I could have been clearer.
0:04:15
aeth
A minimum of two calendar days because sometimes you get to a point where you get stuck and only sleep can solve things.
0:09:32
whoman
i am sorry to hear,i hope your health and quality of life returns to normal and/or improves
0:17:25
drmeister
Is there a lisp function that waits for the user to hit enter or a key - something that will work in slime.
1:26:22
pransninja
True to form, the Chapter 13 of PCL took me as long as every other chapter before it, the chapter title: Beyond Lists: Other Uses for Cons Cells
1:27:43
aeth
Lisp has multidimensional arrays, hash-tables, and other things that aren't cons cells.
1:30:39
aeth
Syntactically, everything's cons cells. The actual data structures that you create are not, though.
1:31:37
aeth
closures, hash tables, multidimensional arrays, structs, standard-objects, etc., couldn't be efficiently implemented with cons cells.
1:37:36
aeth
vectors (including strings) will have an O(1) length and an O(1) elt (or aref). lists will have an O(n) length and an O(n) elt (or nth)
1:38:05
aeth
Vectors have different performance characteristics. And even if they're expressed as lists in source code, they will (usually) be turned into vectors at compile time.
1:39:48
aeth
CL's hash-tables have a different performance trade-off than plists or alists. In theory, plists might be faster for very short things, but hash-tables will win for large data sets.
1:43:18
pjb
Last time I benchmarked, for implementations compiling to native code the break-even point was about 5 entries (<= 5 entries, a-list or p-list are faster; >5 entries, hash-tables are faster), and for byte-interpreted implementations such as clisp, the break-even point is more like 35 entires!
1:44:09
pjb
If you can bound the number of elements, to a small number, it may be even better to use a vector than a hash-table.
1:45:58
aeth
pransninja: You can't expect all implementations to behave exactly the same because maybe one day someone will finish JSCL or write a popular JIT bytecode CL.
1:46:21
aeth
pransninja: But hash tables are in the standard, as are vectors. And a lot of the same optimizations apply to all of the current major implementations.
1:46:49
aeth
e.g. unless you're using clisp, you can pretty much assume that you can make single-float and double-float specialized arrays.
1:47:22
aeth
That's what the standard says about hash tables (or at least one entry point into what it says)
1:48:28
aeth
Vectors will win more often than you think when numbers are involved because they can be specialized
1:49:26
aeth
There aren't any typed lists or typed hash tables (well, they all store type T), so vectors often give more information to the compiler
1:51:25
aeth
Most information is probably specific to SBCL (and/or CMUCL), but a good deal of that will also apply to CCL and possibly even ECL.
1:54:33
aeth
Most optimizations are imo a waste of time. Generally you want to (declare (optimize (speed 3))) and declare any types that are numeric or arrays (if you can provide length information for the array type, that can really help because the compiler may replace repeated bounds checking with one type check at the beginning of the function)
1:56:11
aeth
If everything is of the same numeric type, you can use :element-type in make-array, e.g. (make-array 3 :element-type 'single-float :initial-element 0f0) or (make-array '(2 2) :element-type 'double-float :initial-contents '((0d0 0d0) (0d0 0d0)))
1:56:41
aeth
If things aren't of the same type but are numbers or arrays, typed slots in a struct (defined with defstruct) might work
1:57:32
aeth
If something is trivial and probably never going to change, inlining can help the compiler. Above the function you can do this: (declaim (inline the-function-name-goes-here))
1:59:07
aeth
Not every implementation will use all of the optimization information you give it, e.g. CLISP doens't have single-float or double-float specialized arrays, and just makes them T arrays. I think almost every implementation does accept single-float, double-float and a large number of integer types (e.g. (unsigned-byte 8) and (unsigned-byte 32))
1:59:24
aeth
Only character and bit are required by the specification, but (unsigned-byte 8) is heavily assumed by many libraries.
2:00:52
pjb
aeth: on the other hand, clisp has short-float that will fit immedately into arrays of T!
2:01:27
aeth
pjb: The arbitrary-precision long float is the one reason to use CLISP for code that deals with numbers, afaik.
2:02:31
pjb
pransninja: you can reason with clisp, you just need to know what CL functions are implemented in C and what are implemented in lisp!
2:02:52
pjb
If you write your function to process your data with CL functions implemented in C, then it'll be fast. If you do it in lisp, it'll be slower.
2:03:56
pjb
So what's funny is that basically you must adopt a style opposite to what you'd do in sbcl to write efficient code in clisp :-)
2:04:32
aeth
pransninja: For advanced optimizations, you might be interested in specialization-store. https://github.com/markcox80/specialization-store/
2:05:27
pransninja
at this point, I would like to learn the basics of how you go about optimizations in lisp
2:06:03
pransninja
Though, the fact that optimizations depends on the compiler, which is fair, but still, makes it hard.
2:06:55
pjb
pransninja: it goes like this: you write code that works, without having to deal with memory management or array overflow, because this is controled by the implementation. Once you have something that works, since you've spent 1/10 the time you'd have spent in C, you are left with 9/10 of the time to think about better algorithms. So you can implement them and obtain faster results.
2:13:00
shrdlu68
pransninja: When compiling with slime you get optimization tips (at least using SBCL)
2:13:54
aeth
pransninja: The list I gave is pretty much all you need, except perhaps with the added advice to preallocate things before large loops. Consing (heap allocation) in large loops might hurt performance.
2:14:17
aeth
CL is not a pure functional programming language. People are fine with using things like setf when it helps performance
2:15:45
Pixel_Outlaw
I think it's less /functional/ to mandate a single style at the expense of the programmer's style.
2:15:54
aeth
Most of the advice is about providing array or number type information to the compiler. That's because functions like + and map are type-generic, but can be inlined by the compiler if the type is known. A lot of type information will be given to the compiler just by the function call. e.g. you can only use car on a cons cell
2:19:09
aeth
(Providing the array types can potentially also do two other things: remove bounds checks and tell the compiler the type of the thing that it gets with aref)
2:33:20
aeth
pransninja: What are you interested in optimizing, btw? If it's a program that essentially uses no numbers anywhere, almost all of the advice I just gave is worthless.
2:36:05
aeth
Generally, I optimize on SBCL and hope it works on the other CLs because they just don't expose as much useful information. An almost-complete implementation called Clasp (a C++ and LLVM CL) might, though. And SICL (not anywhere near complete afaik) is designed to be very easy to debug.
2:37:24
aeth
Only optimize the parts that matter, though. You can spend literally forever getting an extra few percent, and the more specific the optimizations are, the less likely they are to be portable away from SBCL.
2:41:14
aeth
(I think the point where you've gone way too far is probably if your code has implementation-specific optimizations all over the place. And if you're inlining assembly...)
2:50:51
aeth
Afaik, for anything that can be expressed as a specialized array, vectors will win unless you construct those benchmarks carefully to have lists win. Lots of inserting in the middle, maybe?
2:52:35
aeth
For the best performance with arrays, though, you'll want known length and you'll want an :element-type that actually gets used (not just a T array).
2:55:03
aeth
So the most dramatic wins for vectors over lists would probably be something like 4x4 matrix multiplication.
2:56:32
aeth
(especially when the matrix has the :element-type defined as single-float or double-float)
3:01:10
aeth
So, afaik, Common Lisp is almost an acceptable FORTRAN now. It looks like it's good enough for Maxima (a CAS program) to use f2cl to compile Fortran to CL. https://github.com/andrejv/maxima/blob/fc2d2c3d0cc532275ac060d46924c26afc667c50/src/numerical/f2cl-lib.lisp
3:02:02
ebzzry_
aeth: searching for the existence of an element is generally faster with vectors, right?
3:03:03
aeth
That sounds like something that should (theoretically) work equally well with either sequence type, so benchmark it!
4:50:12
jmercouris
whoman: "forests are contained in seeds", I feel like there is some profound meaning to this, but I'm not seeing the connection here
4:51:05
whoman
if morning is the seed for night, how we nurture and water this, will bloom into the night. and vice versa, how night fertilizes the next morning
4:51:25
whoman
so you may be having good nights because of bad mornings, but having bad morning times because of good night times ...
4:53:26
defaultxr
has anyone noticed weird behavior when using quoted lists in tests in fiveam? i.e. if i use '(1 2 3 4 5) in two different tests, and one of the tests modifies its list, it affects the other test. doesn't happen if i use (list 1 2 3 4 5) instead. but it seems like it shouldn't happen at all. didn't happen when i was using prove.
4:56:43
defaultxr
i'll try installing another and installing quicklisp on it, etc, if you think that will make a difference
4:57:33
jmercouris
I'm just asking general troubleshooting questions, it sounds a very strange error beacause the quoted list should not share context with another test, and I am thinking it may be some strange bug
4:57:59
defaultxr
the tests seem to be running concurrently based on some print statements i added to my code while i was testing
4:58:20
jmercouris
I also don't know what the difference between '(1 2 3 4 5) and (list 1 2 3 4 5) on an implementation level is
4:58:53
jmercouris
maybe there is some strange compiler optimization behavior going on with contexts, that's my best guess
4:59:05
whoman
there shouldnt be any real difference, not like how its affecting the situation there
5:00:27
defaultxr
it doesn't, if the two lists are different. i'm guessing it has something to do with this: https://stackoverflow.com/a/578365 "DO NOT USE QUOTE TO CREATE LISTS THAT YOU WILL LATER MODIFY. The spec allows the compiler to treat quoted lists as constants"
5:03:26
|3b|
PUSH doesn't modify the list stored at that place when called correctly though, it just changes the contents of the place to point to a list whose CDR is the previous list
5:04:35
|3b|
if that previous list was a literal, you are allowed to modify the car/cdr of the new value, since that cons was created by PUSH, but you are not allowed to modify any car/cdr past that, since they are from the literal list
5:05:39
jmercouris
I assume pop does actually modify the list instead of returning a copy of the list with the element missing
5:07:06
|3b|
(theoretically it still remains unchanged even if you don't, but GC will may affect in ways you can no longer detect, but which wont affect the behavior of your program)
5:10:30
|3b|
right, nreverse may modify the structure of its arguments, so shouldn't be called on literals
5:11:01
jmercouris
So basically if you are manipulating a piece of data over and over again to avoid gc you might use a recycling function instead
5:11:46
|3b|
note that not all of them are /required/ to work in-place, so probably should check the spec (and/or rethink the algorithm) if that matters a lot
5:13:19
|3b|
expense of GC depends on your data to some extent, lots of conses is more expensive to GC than same amount of storage for vectors specialized for things like fixnums or characters that can be known not to contain other objects
5:14:37
|3b|
when it is invoked depends on the implementation, usually in some way related to amount of allocations
5:14:37
aeth
|3b|: Does that mean one big 2D array is better than a vector of specialized vectors because the latter has a T vector that has to be walked through?
5:16:00
jmercouris
|3b|: What is the expensive part based upon the number of cons' is each cons cell it's own object that must be free'd?
5:16:11
|3b|
right, though small effect on GC time might be outweighed by increased costs in the actual code if the abstraction is worse
5:17:11
jmercouris
basically on a system level here, when we run a GC in lisp, are we actually freeing the memory, or is it just now available within our loaded lisp image as "free" memory?
5:17:31
|3b|
jmercouris: speaking very generally, GC tends to involve walking through all objects on the heap starting at for example a register or other known starting point to see what is still 'alive'
5:17:57
jmercouris
furthermore, is this memory every coalesced or just exists neubulously within the lisp image, and then has to be coalesced to reduce the size of the image?
5:18:26
|3b|
if you have a 1 million element list of numbers, it has to look at 1 million conses. and at each number to verify it is just a fixnum/single-float/etc that doesn't need further processing (and if not, walk whatever is there)
5:18:55
|3b|
if you replace that with an untyped array, it skips the million conses, but still has to look at the million values
5:19:34
|3b|
if you switch to a specialized array, it can say "this 1 array only holds fixnums, so it can't hold anything else i need to look at" and the whole array is 1 check
5:19:40
jmercouris
what is the garbage collection strategy in lisp? is it different across implementations?
5:20:04
jmercouris
So there exist some optimizations for the compiler to be more efficient, makes sense