Learn Lisp the Hard Way
learnlispthehardway.org
learnlispthehardway.org
Just to put my two cents in, as a general reply to a lot of comments here... this is a very, very early draft in progress, and I didn't expect anyone to pay attention to this project, let alone post it everywhere. It needs a lot of work, particularly in toning down the Lisp Evangelism, and staying true to the methodology without accidentally parroting Zed Shaw's voice.
Zed Shaw: it means a lot to me to get your perspective here. Yes, you and your series ultra-inspired me. I've wanted to write a book on Lisp for a long time, but it wasn't until I was pointed to your series that I felt like I could give Lisp the perspective it was missing. I'll make a point of editing the Preface more carefully---everything that's up there so far, I wrote off the top of my head with very little editing, so I guess in following your method and format I accidentally used some of your words as well.
Thanks everyone!
The intro is a little bit copied but it's fine since he is keeping to the idea and the "rules" I have, but could be nicer if it was in his own voice more. Who knows, maybe he does write like me a lot or he's just ultra inspired.
The big reason I say people should use their own words, apart from copyright, is that if you're writing one of these books for a programming language you love then your words will express that better. You'll say things that come from your community and culture, and you'll give away a sense of what you like about that language. When people copy what I say the prose comes out obviously not by them and not for that language.
Anyway, this is pretty cool and I hope he works on it some more.
> The Little LISPer is based on lecture notes from a two-week ``quickie'' introduction to Lisp for students with no previous programming experience and an admitted dislike for anything quantitative. Many of these students were preparing for careers in public affairs.
I don't know exactly what that means, but it sounds university-level?
All the examples are about food, and there's cartoons littered throughout. There's a bunch of books that seem to be of that tone (Learn you a Haskell, Land of Lisp, Realm of Racket, Learn You Some Erlang), and I found myself instinctively recoiling from all of them (I haven't read the Erlang book, but it seems very much in that style).
I think it's important to have lots of different styles of books for learning a language, because I think different people respond better to different approaches, but selfishly, I wish every language had an equivalent to "ANSI Common Lisp" (by this site's benefactor emeritus) and Real World Haskell. I am also a big fan of the way Zed chose to lay out his books.
edit : I can't reply to you, but re-read what I said. I am making the point that I believe Land of Lisp to be for people coming from other languages, whereas I think that "learn X the hard way" is better for people new to programming altogether.
The parent of my reply is pointing out to zedshaw that "Land of Lisp" is a good beginners book. I am adding that it's my opinion that it's a good "beginner at lisp" book, and not an overall "good-for-beginner-programmers" book.
To quote from the book page:
Along the way you’ll create (and play) games like Wizard
Adventure, a text adventure with a whiskey-soaked twist,
and Grand Theft Wumpus, the most violent version of Hunt
the Wumpus the world has ever seen.
If someone would like to argue that it does not have a "game approach", I would like to see the specific reasoning as to why.
Though, I have absolutely nothing to back up my thought on this. Would be curious to see any studies or other such on these thoughts.
Also, apologies for the edit. My main thought was more for the informal nature of Land of Lisp. That is, it isn't "high theory" written for experts, nor is it written for kids.
The title is right, IMO. This is a difficult way to learn Lisp. I'm feeling the burn already.
http://learnlispthehardway.org/book/preface/
> The biggest secret to Lisp is that it is actually the simplest programming language ever created—and that, coupled with its expressiveness and elegance, is why it is favored exclusively by the best programmers in the world.
As a Lisp novice...my thoughts are, "Really?" to both of those assertions. Because the natural follow up is..."So if all the best programmers use it, whatever "best" means, why is it a language that seems so rare in everyday use?".
No need to assert things you can't actually prove or show...it just builds up skepticism before the reader even starts learning. Just talk about the language at hand, or at the very least, do a quick Rosetta Stone comparison of Lisp doing something much more simply than Python/Ruby/PHP, and that's all you need to write in the intro.
I stumbled into Lisp some fourteen years ago when a hard copy of the book landed my way.
The book is now freely available in electronic form (and has been for years): http://www.cse.buffalo.edu/~shapiro/Commonlisp/
>Is Lisp as hard as people say it is?
>No. Lisp is actually the simplest programming language, and has no syntactic cruft.
I always see this used when claiming certain languages are easy to grasp. "It's not complex at all! The syntax is incredibly simple!" x86 assembly also has very simple syntax but it's not too easy for beginners to write in, beyond very simple and small programs.
No. Lisp is actually the simplest programming language, and has no syntactic cruft. While it wasn't designed to be “easy to learn” like Swift, Python, Ruby, or Basic, there is less overall to learn and you will be writing real, useful programs in Lisp sooner than you could with other languages."
Is it necessary to put strong subjective statements that have no supporting links or proof? Also, are you seriously saying that /Common/ Lisp is the simplest language? (from FAQ: "Lisp — the friendly nickname for Common Lisp")
Of course, simple syntax is nice, but it doesn't actually get you very far by itself.
But seriously - i've been wanting to learn a lisp for a while now and this seems like an accessible way to go about it.
No. Lisp is actually the simplest programming language, and has no syntactic cruft. While it wasn't designed to be “easy to learn” like Swift, Python, Ruby, or Basic, there is less overall to learn and you will be writing real, useful programs in Lisp sooner than you could with other languages."
It's like a never-ending stream of lies, every word being a little more absurd than the last...
But is it?
++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.I'm learning and enjoying clojure, though!
How To Design Programs for those interested in picking up Scheme: http://htdp.org/
The thing with imperative programming is that you don't really need to know the language to at least get an idea of what's happening.
Lisp is so dense that while you can pack an unbelievable amount of programming into a small chunk, approaching it as a beginner is daunting. There isn't a really good way to 'build' on an algorithm and learning it is significantly harder than learning C# or Java or even better yet, Python.
It's like saying, 'Linux is easy to learn! You can do so much in so few characters! It's so powerful! And look, robust manual pages for all!'
Yeah, that's true, but handing a user some pipes and greps isn't going to explain what the hell they actually do or better yet, how to leverage that into something useful. It's just going to look like greek to anyone who sees it and a huge effort has to be made to get to the point where you can even begin to understand what's happening.
Imperative programming doesn't ask you of much. 'Here is a class. Here is the main method. Write some stuff in here. Here are some basic methods in the default libraries and their expected inputs. It's going to execute line by line. Go nuts.'
And that's really the difference here. Lisp asks a lot of the user up front. Python doesn't. C# doesn't. Fuck, Python is so loose that you don't even really need to know what any of the structure is to start writing something that kicks back some output. Yeah, as a group that understands Lisp and Scheme and Haskell and F#, it's really easy to say, 'Lisp isn't THAT hard', but that's bullshit. Lisp IS that hard. Lisp is a very difficult language to pickup when you are starting at square one and it's only marginally easier if your background is purely imperative languages. Misrepresenting that is a bold-faced lie.
Take any LALR(1) defined programming language. Now write it in one line without indentation. How easy is it to parse (for you, human)? We rely on other clues to grok languages, like indentation. You cannot really "cheat" in parsing; if the machine requires a 600 state transition graph with a push-down stack, that translates into difficulty for you, also.
Lisp is obviously parseable by humans; there are people who easily write and maintain large, complex Lisp programs.
First, I don't want to have to turn myself into an LALR parser to read some code.
> What is hard for the machine is hard for you also.
But what's easy for the machine may well not be easy for the human. LZW isn't very hard for a computer, but good luck reading it.
Syntaxes that may be equivalent to the computer may well not be for the human. Yes, a human can train itself to read that stuff, but if the language designer made more humane choices, the language would be easier for the humans.
Note that this does not directly address how hard it is for humans to read Lisp. It merely addresses the parent's comments.
Humans do not count parentheses and keep track of nesting levels when reading Lisp, any more than they go through LALR(1) state transitions when reading C++.
We structure the code in 2D, and use visual cheats.
With Lisp, there is no clear distinction between "language" and "library".
In any language, code is hard to understand when it uses a lot of external symbols from a library.
No matter how well you understand C, if I suddenly give you a tarball of the USB subsystem of a kernel you've never worked with, and open a random file, it will look like gobbledygook, even though you "understand" the declarations at the "language level".
Most operators in Lisp code are essentially library symbols; and if you're missing some key symbol (such as the outermost one), you might not be able to understand it at all.
Lisp readability requires not only nice code structure, but a decent working vocabulary: enough vocabulary that you're not tripped up by the standard things that are in the language, and you know what is in the language and what is defined by the program.
For instance if you see some (macrolet ...) form and you have no idea what that means, you may be stuck. What is macrolet? Did the program define that somewhere? An experienced lisper doesn't bat an eyelash. Of course she knows what macrolet is: it's a binding construct for making lexically scoped macros, doesn't everyone?
(But at least you know from the unambiguous syntax and formatting clues what goes with what: what parts of the whole thing are arguments to that macrolet, and which are outside that macrolet! So when you look up macrolet in the reference manual, you know exactly what is being passed to it and can figure it out without any undue difficulties.)
Completely and utterly false. Lisp's s-expression syntax is trivial to parse because it is so regular.
The thing with imperative programming
Common Lisp is multi-paradigm, as mentioned in the site's FAQ. You can write imperative code all you want.
For example, IME delving into the codebase of hunchentoot was way easier than django's.
Because I've done more Python working, reading Django's source is much easier for me than most Clojure code (even my own), but that's not to say the same for everyone else.
These are after all languages (even if they are artificial). The human brain is really good at understanding a wide variety of linguistic constructs, the main issue is familiarity and that changes from person to person.
From what I understand the hardest thing to teach new programmers coming to Java or Javascript or even Python is assignment and mutability. That has a huge cognitive overhead.
Contrast that with the lambda-form structure and substitution method of evaluating expressions in Lisp.
(function arg1 arg2...)
You color your argument with a preference for imperative programming by over-simplifying Java; arguably one of the more difficult languages to teach beginners. The venerable, "Hello, world!" exercise is an illustrative example.
Again contrast that with:
(format t "Hello, world!")
> Python doesn't. C# doesn't. Fuck, Python is so loose that you don't even really need to know what any of the structure is to start writing something that kicks back some output.
again, not unlike lisp.
> Lisp isn't THAT hard', but that's bullshit. Lisp IS that hard
Care to back up that claim? AFAIR The SCIP barely spends a page explaining the semantics. The CONCEPTS in teaches are hard(er) but they are not lisp. In fact one of the reasons the SICP was written in Scheme is so that you _don't_ have to waste half a semester teaching the language before you can get to the fun, important, useful stuff. The little schemer doesn't spend much time teaching lisp either.
(format t "~{~@(~A~)~^ ~}, because ~{~A~^ ~} is easier!" llthw (cddr llthw))printf("something %s then %d finally %f!", "asd", 1, 1.2)
As mentioned, there is a loop built into format. Since lisp also has a (list) function eg: (list 'a 'b 'c 1) I still don't see an argument beyond familiarity with the C style printf syntax for why format is bad/unreadable.
So there's a lot more power here than in 'printf' control strings. If you find the more exotic notation unintuitive -- and you certainly wouldn't be alone -- you don't have to use it.
Lisp as an idea has a simple syntax but Common Lisp isn't even close to that platonic ideal.
There isn't any syntactic cruft in Lisp that will have you scratching your head as to what goes with what.
There are semantic head-scratchers related to syntax, like working out the implied actions of complicated, nested backquotes. There is never a question of syntax, though: nested backquotes are not ambiguous syntactically: they are just nested lists, with some sprinkling of a simple prefix-based notation throughout (splices and unquotes).
Lisp is a difficult language due to it's density and unreadability.
Useful stuff hasn't been built in functional languages until very recently, exception being some AI. Haskell and friends are making functional languages cool and useful (and that's great!) but if you want to build something useful as soon as possible, learn .NET, Java, Python or Ruby.
You might enjoy this: http://www.infoq.com/presentations/Simple-Made-Easy
The idea that you can write a useful program in Lisp faster than in other languages is pretty unsupportable. For most users, the time and effort spent getting Lisp up-and-running on their machine of choice will already have lost. Incidentally, I played with the interactive REPL and it wouldn't advance beyond the second page.
And, if you do write a useful program in Lisp, you run into the deployment problem. The deployment problem is pretty bad. Apple's Advanced Technology Group at one point had one of the highest concentrations of Lisp-heads in the world and produced a bunch of stuff like Dylan, Sk8, etc. that was intimately tied to their Lisp implementation. Not only was this not cross-platform, and pretty hard to distribute and deploy even on the platform it was created for (680x0 Macs) it was killed by the transition to PowerPC.
This isn't as big a problem if you're writing server software, but it's absolutely disastrous if you're writing desktop or mobile software.
One could show someone how to do something useful and deployable in Python, PHP, Perl, Javascript, or whatever in a few minutes and chances are they could have a usable dev environment set up in a few minutes.
And for any language that's popular now, there was a time that it wasn't yet popular, and deployment was a pain.
So I think you have it backwards: Lisp is not unpopular because it's hard to deploy; it's hard to deploy because it's never cracked the popularity threshold.
Why is this? It's because they can live in, and interact with, the common linking and loading ecosystem that the rest of the world lives in: the C ABI. If you can link your output into something that respects the C ABI, you can deploy it[1].
Common Lisp implementations could immediately solve their deployment problem by living in this ABI. So far, the only one that has done so is ECL (which is an excellent project).
[1] A few alternatives exist. The Java and .NET ecosystems are also viable link targets (as I think Clojure has proved).
But this only restates the point. It's easy because those things are popular. Try deploying an executable that requires a shared library that you can't download with your package manager, and you're pretty much back into the same pain.
Using the C ABI helps if you want to link against other code that uses it, though it isn't strictly necessary (pretty much all these language implementations have foreign call mechanisms). But this is a development issue, not a deployment issue.
ECL does make it convenient to build standalone executables, but most CL implementations can also do this.
Lisp systems like LispWorks can generate typical platform shared libraries.
Many can easy embed C-code.
Some compile to C, which than can be embedded. ECL is only one example. Others are mocl or the ECL-related systems.
Lisp is notoriously hard to deploy. Code is not portable between different lisp implementations. Apple's ATG ended up axing many projects because they had so much trouble moving their lisp from 680x0 to PowerPC.
The fact you talk about "your system's package manager" ignores my point -- I'm not saying Lisp is especially hard to deploy to servers (although it is -- but this is, as you say, a popularity issue; and it would be far worse if the world of servers hadn't converged on a small number of very similar platforms). I'm saying it's hard to deploy to desktops and mobile, which is where most of the "useful" programs people might want to write still live.
A huge part of Lisp's problem is fragmentation. Which Lisp? Aside from fragmentation in Common Lisp itself, there's all the not-quite-Lisps around, ranging from Arc to Scheme to Clojure to sheesh-I-really-have-no-idea. And of course this is because once you start coding in Lisp there's an overwhelming urge to abstract away difficult things in your own clever way, perhaps even hacking the language itself, and pretty soon your little world is utterly unique.
Another great, simple language in the exact same boat is Forth.
Lisp has no syntactic cruft? It has (almost) no syntax, so there's less room for cruft. That said... cons? car? cdr? That's your syntax? That's not cruft? Seriously? There may be less total cruft, but the percentage of cruft might still be higher...
There's less overall to learn? If you mean to master the syntax, sure, that's true.
You'll be writing real, useful programs in Lisp sooner than you could with other languages? That's a much more arguable point. There's more to being able to effectively program in Lisp than learning the syntax (as there is for every language). Is that "more" easier to learn for Lisp than for other languages? I have no data, but for the web site's claim, I'd at least say "citation needed".
If you're a bright developer, who puts in time eagerly, it will take at least six months before you begin to "get it".
At that time you may start itching to evangelize to others, but those who have not put in the time will not get it.
It's not realistic to try to make someone see in one or two e-mails or postings what took you a year to see for yourself.
A recent example from personal use is continuations. Scheme has them as a first-class object. Common Lisp does not, but a common claim is that you can write macros to provide continuations. Some people have: there's "cl-cont" available on Quicklisp, which is a macro that will code-walk your functions to turn them into continuation-passing style and thus allow you to use continuations in those functions.
So that's great, right? Common Lisp now totally has continuations? Not at all. In order to get this feature, you need to wrap ahead of time (specifically, at compile time) the functions you want to be continuable, and all of their callers, in this macro. You cannot simply use a function that you've been given as part of a continuation, it had to have been compiled under this macro.
That's where the power of macros completely falls down and, in my opinion, gets completely overblown. Yes, your language is extendable, but your extensions are limited to computation and source-to-source transformation at compile time. You can't apply any of that power to already-existing artifacts.
Which is not surprising. Actually nobody with a clue makes such a claim.
Still, Lisp macros have a wide variety of very useful applications.
> Yes, your language is extendable, but your extensions are limited to computation and source-to-source transformation at compile time.
Still quite useful. From relatively simple stuff which makes to code more readable to complex macros like ITERATE.
> Which is not surprising. Actually nobody with a clue makes such a claim.
Most Lisp books make this claim.
For sure not.
1. lisp got a lot of stuff wrong; there's really no reason not to use scheme.
2. lisp syntax is more something to overcome than something to become "enlightened" about. Language syntax no longer has to be motivated by ease of parsing.
3. Dynamic typing only gets so enlightening. At the end of the day, type theories are where the rubber hits the road.
4. Macros don't excite me much. I mean, they're cool, sure. Okay.
At the end of the day, there's a lot more exciting stuff out there (e.g. any math class beyond the calculus sequence or so) that people get way less worked up about.
It's possible to understand lisp, think that there are important ideas there, but not go around evangelizing. Most smart people who study something non-trivial don't evangelize.
Scheme got a lot wrong from a practical perspective. Use Lisp instead.
Type theories are over-hyped. 99.99% of all software is written in languages without advanced type systems.
Macros are nothing for 'excitement'. They are a tool. They enable the user to write source transformations, which has several applications in Lisp: control structures, compile-time computation, etc etc.
But Im not going to get into a language war.
Stepping back to the original point, there are other significantly important/powerful ideas in the world, and lisp users are somewhat over-the-top in their significance-to-hype ratio.
> Stepping back to the original point, there are other significantly important/powerful ideas in the world, and lisp users are somewhat over-the-top in their significance-to-hype ratio.
Many of the powerful ideas in software development are available in Lisp.
And there's a whole hell of a lot more in the world than software development...
To the extent that lisp captures any of these other foundational ideas/theories/techniques, type theory does better (which is what I was pre-empting with my original reference, not the role of type systems in the world of practical software development).
Lisp is not a version of lambda calculus. It's a programming language. Macro programming in Lisp works fine in many cases.
> type theory does better ... not the role of type systems in the world of practical software development).
Lisp is about practical software development.
I'd argue that there are lots of other settings with ideas a powerful or more powerful than whatever it is each individual evangelist feels someone should get out a lisp. Yet none of these other things have enlightened evangelists pushing the product.
That's all I'm saying.
It's been my experience that most things are tractable once you spend long enough staring at them.
If you care enough about a subject to have strong sentiments like "never-ending pack of lies" then your time would perhaps be better served by spending time with the "adored" object, rather than these comments.
Keep in mind too that different Lisps have different syntax. The only thing in common between them is Polish notation, S-expressions and a macro system. A Clojure program and a Common Lisp program look and feel very different.
As a transhumanist myself I resent the arrogance that led to this ridiculous appropriation. Yes, Lisp is pretty great, but the use of other languages is not some grave cultural defect through which you can glimpse at all the badness in the world.
If the goal here is to evangelize Lisp, radiating this kind of pomposity seems like a questionable move because it reflects badly on the community you are trying to win new members for. Worse, this could be interpreted as willful cluelessness in the face of the rich multi-language ecosystem potential readers are living in.
As far as the singularity is concerned, monocultural boneheadedness is not something people associate with technological progress.
From your link:
> The first self-modifying AIs will hopefully be written in functional programming languages, so learn something useful like Haskell or Scheme.
> 1958 - John McCarthy and Paul Graham invent LISP. Due to high costs
> caused by a post-war depletion of the strategic parentheses reserve LISP
> never becomes popular[1]. In spite of its lack of popularity, LISP (now
> "Lisp" or sometimes "Arc") remains an influential language in "key
> algorithmic techniques such as recursion and condescension"[2].Willful ignorance about other languages and their features is as much a cultural failure as, the hypothecial, unwillingness to learn about Lisp.
Every language has its use, but really we ARE wasting time by splitting the worldwide community of programmers in different languages.
Look at how most programmers love one language and advocate it's the best there is. That's called a split.
Aren't we supposed to not reinvent the wheel?
Even if such a language existed (be it Lisp or not), which is unrealistic, there is still a second aspect to the whole thing: programmers' brains. Different languages map differently to different kinds of brains, and that's a very good reason to explore multiple concepts in itself.
The Split is the natural way to explore a large search space using different strategies. It happens all over nature, and it's the way human-powered research works as well. Monocultures don't perform nearly as well. Yes, there is some effort wasted, but you can rarely ever come to an objective consensus where this waste actually occurs - except, typically, in hindsight.
Also, there is quite a bit of cross-pollination of ideas happening among different environments and languages, so advantageous traits do get passed around beyond their initial ecosystem.
I imagine cross compilers and common runtimes will get more popular, too, now that we have the processing power - and that's also a good strategy do deduplicate effort.
The only thing that really strikes me as a bad strategy is militantly advocating one programming language as the master race. You're not even doing the "pure" in-community a favor by denying that concepts from the outside world might occasionally be useful. Instead members are reduced to armchair criticism along the line of "yeah, nice library, but you didn't write it in Lisp, so at the end of the day nothing at all was achieved."
It seems as though the author is trying to sell a religious experience to his readers. If that is the case, that's interesting in the sense that it is certainly unlike any other programming text I've read. I personally think evangelizing Lisp should be in the form of making it more familiar, human, and relatable to the average programmer, but I can't help but to respect the sheer uniqueness of the approach.
[1]http://lemire.me/blog/archives/2010/05/31/computer-science-i...
How circular! A Lisper would respond that the very passage you critiqued is the appropriate response to your critique---that Lisp is coming, no matter the tone, and our complaints or praises will have no effect on the final outcome.
Perhaps Lispers would do well to be less pompous, but that is for their welfare, not Lisp's.
At best, this is a religious point of view, and at worst it's also a matter of being part of the in-group - which means this opinion is calcified because it's a critical part of these programmers' identity.
I generally don't like to comment on these kinds of threads anymore than I would on political or religious ones. However, this thread is about outreach to people outside of the cult. Continually forcing the impression of being a cult might well serve to recruit more followers, but I'm wondering: does it really have to be a dogmatic movement? Isn't the larger opportunity here to try and reach another kind of person?
I know there's a taboo in this community about addressing aggressiveness and arrogance, and maybe that's an excellent policy to prevent flame wars. However, I think it's a mistake to overshoot this target by accepting abrasiveness and fervor as valid replacements for reason and reflection.
Q: Is this site affiliated with Zed Shaw and Learn Code The Hard Way?
A: No. This is a separately run and managed site, based on the format of Zed Shaw's LxTHW open-source package [1] for writing your own programming language course. You should check out the project and see what others are up to! More information is available at: Learn Code The Hard Way [2]
Zed A. Shaw created project Learn X The Hard Way 2011-08-29 22:06:48 UTC This is a skeleton book project that makes it easier to start working on a "Learn X The Hard Way"...
Also, read the README: https://gitorious.org/learn-x-the-hard-way/learn-x-the-hard-...
1. You can't really trademark titles of books, and I wouldn't want to in this case because there needs to be more books in this style. This method works for beginners, and works really well, so I want there to be more.
2. I created the repository so that there's an even lower barrier to entry than having a title to copy. I actually need to update this repository, but if I made it then I want people to reuse the methodology and make their own.
3. My only complaint would be when people rip off my words. If someone wants to write one of these, they just need to do their own writing in their own words and not copy mine.
That's my stance on it. I like people copying the title and method as it means there's more books that will help people learning to code. I just don't like them copying what I wrote.
I do support books like this as I think there needs to be more "trainer" style books, especially for beginners, because they work.
I like lisp, but this kind of mystical gobbledeygook is not helpful. It's worth noticing that mystics and lisp-ninnies are alike in a very important way: promising much, and delivering little. The people who actually accomplish things in lisp (Yann LeCun, Richard Fateman) do not speak in this preposterous mouth foamy way. They also don't work for overt frauds like d-wave.
It may be better to leave the intro part for the end as it may alienate programmers that have preconceived notions about lisp based on hearsay and not actual experience (i.e. it's enlightening, it's old, full of cruft, hard to read, it's functional, Clojure is the future of lisp).
It is also very much a WIP that the author didn't submit so keep that in mind.
I hope he gets to writing the chapter on Quantum computing: http://learnlispthehardway.org/book/3-14-0-quantum-computing...