<ixelp>
The package-inferred-system extension (ASDF Manual)
<dnhester26>
it uses :use-reexport in the all.lisp examples. Wouldn't it make more sense to use :import-from to avoid collusions?
<beach>
Some people do, but I don't. I forget exactly why. Is it that each file must be in its own package?
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<beach>
I just remember that there was some ridiculous (to me) limitation that I couldn't accept.
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<yitzi>
The idea of putting an entire package in one file is absurd. As is the idea that there is a one-to-one correspondance between packages and systems. Its just a terrible idea, imho.
<beach>
I totally agree.
<pfdietz>
I've used p-i-s. Sticking everything in a single file is a downside. It would be nice if there were a way to have the best of both worlds. Maybe associate packages with directories, not files?
<yitzi>
Yeah, I don't even like Lisp files that more then a couple hundred lines long. That is what separate files and hierarchical files systems are for.
<pfdietz>
The problem then would be describing the dependencies of files in that directory.
<yitzi>
That is what the ASD is for. I am missing something?
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<dnhester26>
yitzi: can you please explain why not use a package per file? why is it absurd? Sorry if it seems dumb, I'm just coming from a java python background where every file pretty much is it's own package. lisp packages have nothing to do with that because they are ways of bringing symbols together, but java to the extreme every file is pretty much just a class, and you import based on the directory path to get the class. it's pretty stra
<dnhester26>
ightforward and removes the need to write a build file like .asd, which is what's bothering me a lot
<paulapatience>
Section 12.1.1.3.1 says the logical operations do, but makes no mention of it in 12.1.1.3.2 for byte operations.
<dnhester26>
asdf just finds it because it's a .asd file even though it's not on the same directory it doesn't matter, it just traverses searching so I don't have to worry about it. Correct?
<dnhester26>
Is that the best way, to make a .asd file generally for every foler
<dnhester26>
to avoid making a big bloated .asd file in the top directory?
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<dnhester26>
are system names and package names completely independent from each other?
<yitzi>
dnhester26: Putting a single package into a single file is only appropriate if the package is very small in terms of the lines of code. For anything else more than ~500 lines of code it can be confusing (at least to me) to have it all in the same file. Instead break it up into logical groups of functionalitity for each file. common-lisp is a single package, can you can imagine the entire code-case of a CL implementation being in a single file?
<yitzi>
You can have multiple packages per folder...thats up to you, btw.
<dnhester26>
yizti: what is the meaning of a package beyond a grouping of symbols? when I think of a package I think of a group of symbols that provide certain functionality, but according to that each file you are describing should be in it's own package. Why keep them all in one package?
<yitzi>
I think having larger packages versus lots of smaller ones is pretty subjective. I just try to group them by the logical functionality groups that help me visualize the problem.
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<beach>
dnhester26: When you :EXPORT something, you give it a string designator, so that will create the symbol in the package you are defining, or export an existing symbol otherwise available in the package.
<beach>
dnhester26: You can think of the package as the unit of encapsulation. It says what symbols are available to client code.
<beach>
dnhester26: But most of the time, the definitions named by those symbols, like functions, classes, types, etc., represent a lot of code, and it makes sense to put them in separate files.
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<beach>
dnhester26: For example, you might want one file with definitions of generic functions without associated methods, and another file with class definitions, and a perhaps several files with method definitions for the generic functions.
<beach>
dnhester26: In other words, the Common Lisp package system plays the "encapsulation" role of classes in most object-oriented languages, whereas Common Lisp classes play the role of the "representation" role of the classes in those languages.
<dnhester26>
beach: thanks for the explanations
<beach>
dnhester26: It is a dumb idea to have both encapsulation and representation represented by the same language element. That's probably why code in traditional object-oriented languages get very complex.
<beach>
dnhester26: Sure. I hope it was somewhat clear.
<dnhester26>
is there a way around having to define the .asd build files with serial or depends-on? In a lot of other languages, the build is just implied by the way the code is written without having to explicitly state it
<dnhester26>
why is it a dumb idea? because encapsulation is not for all other classes, just the ones outside of that particular functionality?
<beach>
It is not a great burden. You add a line each time you add a file.
<beach>
dnhester26: Because it gives you less flexibility.
<beach>
In Common Lisp, you typically have several classes defined in a single package, because all those classes are logically part of the same "module".
<dnhester26>
I get errors all the time from defining circular dependencies or forgetting to add the line and I just find the whole managing of a massive file of dependencies a pain. But I can see that I may have been structuring my code in the wrong way, I just don't see any explanation on the correct way. I'm reading your cluffer to try to understand how. Making a system per folder seems more sensible and I guess forces that all those files be
<dnhester26>
either completely independent of another folder, or if dependent, the other folder cannot depend on it...
<beach>
dnhester26: Yes, the way I organize my code is that a directory contains the code of one "module" and that "module" is defined by an ASDF system definition and a package definition.
<beach>
There are other ways of course.
<dnhester26>
flexibility in terms of what? having another class within the same module access the first classes slots yet at the same time not export the slot accessors from the package so that classes outside the package should not access it as a first measure?
<beach>
Stuff like that.
<beach>
So in my code, the dependencies are either between modules, as stated in the ASDF system definition, or between files in a module, which I usually turn into a :SERIAL T dependency for simplicity.
<dnhester26>
so module is really a whole working component of a project. In a web app with a model view controller type design, it doesn't make sense then to have those 3 folders mvc, it would be more like a module for authentication with a folder for it and it's mvc files inside that folder, and then each part of the code that can be broken up would get it's own module. right?
<beach>
dnhester26: Classes in Common Lisp are very lightweight. It is common to define a bunch of "mixin" classes, for instance, and they often play not important role to client code.
<beach>
dnhester26: I know nothing about web applications.
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<dnhester26>
thanks, I'm just trying to understand how to structure my code, break up the 40 files in the asd file I have into multiple systems so that it's easier to manage. it's just a model view controller, it's not particular to web apps, desktop apps and anything that wants to separate concerns for displaying data (views), doing business logic (controllers), and data representation (models) has it..
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<beach>
dnhester26: Right, I would then have a module for each independent model.
<dnhester26>
ok, thanks, this was instructive. I wish there was a tutorial or explanation at length of this somewhere. Even if it's an opinionated tutorial, it's better than no tutorial. it's just that the approach is so different from say java python and other languages I've programmed in, that I find it hard to guess the concepts
<beach>
Yes, it is different because the Common Lisp object system is very different from that of most languages.
<dnhester26>
beach: a module for each model you mean the whole class, logic for processing that data in the class instances, and the code for displaying it, all in one package and system. Is that what you meant?
<beach>
No.
<beach>
And I don't know why you talk about "class" here. The module contains what we call a "protocol definition", which is a generalization of an interface.
<dnhester26>
This difference between encapsulation and representation, once you mentioned it in regard to the packages, I understood what you meant, but without thinking about it, I was not aware. I should really read the Keene book you recommended. It's the tradeoff of trying to be productive and code vs taking the time to read that is hard
<dnhester26>
beach: I've no idea what this means in our context: "The module contains what we call a "protocol definition", which is a generalization of an interface."
<beach>
So a protocol contains classes, functions, types, method combinations, variables, etc. that client code can use in a coherent way.
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<beach>
The documentation of a protocol explains the relationship between those elements, like how to create instances of the classes, what class instances can be passed to what functions, what objects those functions return, etc.
<beach>
It also explains what kind of subclasses client code can create and what methods it must then supply.
<beach>
dnhester26: I have an idea. Eclector is a program that implements the Common Lisp READ function. It is highly configurable. It is also well documented. Perhaps you could look at the documentation to get an idea of the concept of a protocol.
<dnhester26>
beach: thanks, I will take a look. I was reading cluffer for an idea of how to structure the code. eclector shows how the code comes together in a protocol. Is this way of using a common lisp way of using it or is it your personal definition?
<beach>
The term "protocol" is used in the CLOS literature.
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<beach>
dnhester26: Oh, another important document is the CLIM II specification. That's how I learned about how to use CLOS and CLOS protocols.
<ixelp>
CLIM 2 Specification — Common Lisp Interface Manager CLIM II Specification
<yitzi>
dnhester26: I was only using that as an example of `:pathname`. That is system is implementing part of the CL spec inside a host implementation so it is a bit unusual in the export list. The actual functions are created by a macro, so its not immediately obvious on first glance.
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<beach>
dnhester26: Speaking about dependencies, I don't see a general way of inferring the dependencies between the components (files) of an ASDF system.
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<scymtym>
dnhester26: eclector mostly shows my preferred style. for example, the ASDF system definitions are in the project root directory. but beach, yitzi and i all use one directory per module and often but not always one file per aspect within such directories like "conditions.lisp", "generic-functions.lisp", "classes.lisp"
<beach>
scymtym: I was pointing to Eclector mainly for the documentation, but that's a good point.
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<yitzi>
I second that. Part of understanding how a system functions is building a mental map of where that functionallity is located and good names like scymtym suggested are really key to that for me.
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<dnhester26>
beach: yuo learned from reading the specification or from coding in the project?
<dnhester26>
yitzi: yeah, ok, I was just reading it to understand what the defpackage was doing in general. That was a different file from the one you sent me. thanks
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<dnhester26>
scymtym beach: ok thanks, so read both the docs of eclector the the code to understand what a protocol is and how to break up the code in modules. CLOS and CLOS Protocol: read the CLIM II specification for the docs or the code?
<dnhester26>
yitzi: ok thanks
<dnhester26>
so there is no way in common lisp unless we modify somehow how we program to avoid writing a build file?
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<scymtym>
dnhester26: the CLIM II specification doesn't have any code besides examples. i just describes how a CLIM implementation is supposed to work and be used. the described functionality is broken down into named protocols like here: http://bauhh.dyndns.org:8000/clim-spec/8.html#_294
<ixelp>
CLIM 2 Specification — 8 Sheet Protocols
<scymtym>
*it just describes
<dnhester26>
scymtym: thanks. so reading that document is the task
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<beach>
dnhester26: Mainly from reading the specification.
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<dnhester26>
beach: by the specification you mean that CLIM II document you sent?
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<beach>
Yes.
<beach>
In particular, I learned from it that slots are implementation details and that classes are defined by a name, the initargs, and the functions that can take its instances as arguments.
<dnhester26>
thanks
<beach>
That way, whether some datum is stored in a slot or computed, is of no importance to client code, and the module can change between the two without informing the client.
<dnhester26>
what do you mean by slots are implementation details?
<beach>
An "implementation detail" is something that is private to a module and not part of the protocol.
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<beach>
So, for example, if you have a class PERSON, you may have two functions DATE-OF-BIRTH and AGE, but you have no business knowing whether one of them is computed, nor which one in that case.
<dnhester26>
oh wow, even public fields in say another language, here in CL we are saying there's really no such thing? it's only relevant to export a function from a class for accessing and setting the slots
<dnhester26>
got it
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<dnhester26>
interesting. i guess in java the practice was to make getters and setters instead of public fields, which seemed to accomplish the same thing, but it basically allows for changing the internal representation of the data as long as the public function interfaces stay the same, so here too
<beach>
Yes, but we don't call them SET-* and GET-*, and they don't have to access a slot.
<beach>
For example, if a PERSON has an ADDRESS, you might have a function named ADDRESS that takes a PERSON object, and a function named (SETF ADDRESS) that updates the address. The latter would be used with SETF like: (SETF (ADDRESS JANE) <new-address>)
<beach>
And since packages are all about symbols, both those functions can be used by client code if the symbol ADDRESS is exported.
<beach>
But whether the address is stored in a slot of the PERSON object or in a hash table, or somewhere else, is irrelevant to client code.
<aeth>
yes, set-foo is (SETF FOO), get-foo is FOO, and the API is ideally the same except the SETF function (it doesn't have to be a function, though, since you can define your own in one of 3 ways) just takes in one extra argument, but the syntax of calling a SETF function puts that later
<beach>
And I have the impression that get-foo and set-foo are used only to access fields, in which case it is again blatantly obvious what is stored in a field and what is not.
<beach>
Otherwise, all Java functions would have one of the two prefixes.
<aeth>
Since there's no separate dot notation, either, the syntax is entirely uniform and (foo bar) and (setf (foo bar) 42) could be anything.
<reb>
Regarding the uniform access principle page wikipedia page. It's sad there's no Eiffel example. With Eiffel foo.bar can either mean "access the bar field of object foo" or "call the bar method of object foo", which allows refactoring fields into zero-parameter methods and vice versa.
<aeth>
You can even obscure the constructor with MAKE-FOO in which case it's not clear to the user any implementation details at all
<aeth>
reb: You can fix it!
<beach>
reb: But Common Lisp is even better, because slot accessors are just functions that can be mapped over stuff like lists.
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<beach>
reb: That's why initial attempts at Common Lisp object systems were rejected, because they had a different syntax for slot access.
<beach>
And as a bonus, with CLOS we get multiple dispatch.
<reb>
The only thing I really miss about Eiffel is design by contract.
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<aeth>
Seems to be an issue with the Wikipedia article that it's missing Eiffel and CLOS examples.
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<dnhester26>
beach: aeth: thanks for your explanations. sorry for the late reply, I had to jump to a meeting
<beach>
Sure, hope it made things a bit more clear.
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<yottabyte>
in my function I see an underline in emacs saying undefined variable and undefined function in my package, but they're not, indeed the function works as expected. it seems like it's just lost or not keeping track of things correctly. has anyone experienced this before?
<yottabyte>
oh, I just compiled it and now the lines went away
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<bike>
yeah it just keeps those from previous compilations.
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<pfdietz>
Something like design by contract should be achievable with method combination. For example, preconditions/postconditions/invariants in :around methods.
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<aeth>
preconditions can be enforced entirely by the type system if you force type checking (which sadly needs to be done via the MOP) because e.g. SATISFIES types
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<aeth>
or at least, around anything contained by an object
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<aeth>
that gets rid of 90% of the :before or :around methods you'd want, for constructors and accessors
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<lispmacs[work]>
hi, for various nefarious calculation purposes, I was wanting to get the J2000 epoch in universal time. But am a little unclear how I should go about this
<lispmacs[work]>
WP lists the the J2000 epoch in UTC time
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<lispmacs[work]>
Does CL have a way to convert a UTC datetime to UT?
<ixelp>
GitHub - CodyReichert/awesome-cl: A curated list of awesome Common Lisp frameworks, libraries and other shiny stuff.
<lispmacs[work]>
I'm using local-time library, but I need to get J2000 converted to UT first to work with it
<Fade>
I don't know the details of this conversion
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<lispmacs[work]>
okay, thanks. I'm thinking the #astronomy folks might be able to help me out with that
<Fade>
the relation between time and astronomical relations is a little loose. the astronomy crowd would likely be the way. :)
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<edgar-rft>
lispmacs[work]: do you want Common Lisp's universal-time or astronomical universal-time? For the year 2000 this makes a difference of 22 leap seconds.
<lispmacs[work]>
sorry, have to rush away from keyboard, boss calls
<edgar-rft>
no worries, I'm still here for a while...
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