A Haskell Programmer Tries to Learn Racket

http://artyom.me/learning-racket-1

by jackhammer2022 • 12 years ago

257 156 12 years ago

artyom.me

wglb• 12 years ago

Nicely written, and a fun exploration.

gaigepr• 12 years ago

"...but nothing beyond that. As long as Node.js exists in this world, I can't truly hate anything else."

I found this hilarious. I am also rather underwhelmed (to be nice) with Nodejs and a little bothered at its wide adoption.

I have also been learning racket recently; my formal language and functional programming class uses it. I had some previous experience with common lisp but the raw nature of scheme still pleasantly surprised me a little bit.

EDIT: From what I remember, javascript was "inspired" by scheme. Obviously that when well...

MichaelGG4• 12 years ago

I keep flipping back and forth, thinking I don't get it, then thinking others don't get it. Single-threaded JS with callbacks. OK? What am I missing?

The only thing Node has going for it is a lot of networking libraries. It's not fast, the async style leads to callback hell, JS is a terrible language, and their package management system is slow and bloated (or at least the packages are)[1]. Yet people think it's some new kind of thing that's just so awesome, despite MS doing server-side JS in the mid-90s.

Sure, people can use whatever makes them happy. I'm just confused as to why anyone is particularly impressed with Node or JS.

1: Seriously, to automate builds, I ended up saving the node_modules directory then symlinking it in to the build environment. Otherwise a simple CSS/JS/etc. grunt build took 15 minutes instead of 1. And it seems every module pulls in its own copy of dependencies, so you end up with 300-character deep paths. There's no apparent reason it needs to be like this.

mattgreenrocks• 12 years ago

It's popular because people think other people think it's popular.

There's no accounting for taste, but, it won't last. :)

nly• 12 years ago

My theories:

1. Using the same programming language on both sides of HTTP often appeals to a developers visceral sense of elegance, or tidiness, even though it this alone inherently solves no existing problems.

2. It's powered by Googles V8 engine, which means people already associate it with this "super fast JIT" thing that lives in their favourite browser. It must be efficient, right?

3. The crowned alternative is PHP which is slowly becoming Java and alienating, with no disrespect to anyone intended, the less experienced, the "let's just hack a script together" crowd.

pera• 12 years ago

V8 vs Racket: http://benchmarksgame.alioth.debian.org/u64/benchmark.php?te...

ludwigvan2• 12 years ago

Straight from the horse's mouth:

"Node is popular because it allows normal people to do high concurrency servers. It's not the fastest or leanest or even very well put together - but it makes good trade offs in terms of cognitive overhead, simplicity of implementation, and performance. I have a lot of problems with Node myself - but the single event loop per process is not one of them. I think that is a good programming model for app developers. I love Go so much (SO MUCH), but I cannot get past the fact that goroutines share memory or that it's statically typed. I love Erlang but I cannot get the past the syntax. I do not like the JVM because it takes too long to startup and has a bad history of XML files and IDE integration - which give me a bad vibe. Maybe you don't care about Erlang's syntax or static typing but this is probably because you're looking at it from the perspective of an engineer trying to find a good way to implement your website today. This is the source of our misunderstanding - I am not an app programmer arguing what the best platform to use for my website--I'm a systems person attempting to make programming better. Syntax and overall vibe are important to me. I want programming computers to be like coloring with crayons and playing with duplo blocks. If my job was keeping Twitter up, of course I'd using a robust technology like the JVM. Node's problem is that some of its users want to use it for everything? So what? I have no interest in educating people to be well-rounded pragmatic server engineers, that's Tim O'Reilly's job (or maybe it's your job?). I just want to make computers suck less. Node has a large number of newbie programmers. I'm proud of that; I want to make things that lots of people use. The future of server programming does not have parallel access to shared memory. I am not concerned about serialization overhead for message passing between threads because I do not think it's the bottleneck for real programs." https://news.ycombinator.com/item?id=4310723

rdtsc3• 12 years ago

I'm just confused as to why anyone is particularly impressed with Node or JS.

Low barrier to entry means anyone who used to animate jumping monkeys on webpages and now write distributed back-end systems (all web-scale of course).

Kids haven't seen anything else. Maybe took C++ or Java in college, then they see a kid with piercings and a messenger bag and tight pants talk about this awesome asynchronous callback-futures-based awesome frameworks. There is really nothing to compare it to. So they are impressed.

Next level up, write a benchmark. Compute fibonacci, compare with Java, hey not too bad. Even faster than Ruby! Clearly this is the framework of the future.

Maybe read some place about how threads are bad and callbacks are great. And so on.

so you end up with 300-character deep paths.

Hehe, too funny. Actually it just needs to be 260 characters, so 'git checkout blows' up on your unfortunate colleague who happens to use Windows.

kazagistar• 12 years ago

Javascript is fast enough to be usable on a server, Javascript has grown client-side, and you can share code across both. That adds up to something at least reasonably useful and unique.

lucian19002• 12 years ago

The one good thing about the packaging system is that each dependency is its own version, so you can easily load different versions of the same package.

anotherevan• 12 years ago

I wasn't going to bother reading the source article, up until I saw this excerpt in your comment. Now it is added to my reader. :-)

linhmtran168• 12 years ago

I also hate NodeJS for its package manager, NPM. I don't understand the way it manages dependencies and their folder. What the hell is 'node_modules/express/node_modules/connect/node_modules/multiparty/node_modules/readable-stream/node_modules/debuglog/'.

As a result, when updating dependencies with npm, a same dependency is downloaded multiple times.

ludwigvan2• 12 years ago

That is a good thing when multiple libraries you depend on depend on different versions of some other library.

See http://blog.izs.me/post/1675072029/10-cool-things-you-probab...

ripter• 12 years ago

It solves the nasty versioning issues that plague the other package managers like pip and rubygems.

Every package gets the correct versions for all of its dependancies at the cost of taking more hard drive space. Hard drive space is ridiculously cheap so it's a good trade off.

Zoxo• 12 years ago

I like the approach you took to writing this post. This wasn't the typical attempt to summarize an entire programming language in a page (which IMO is done too often, too poorly), but rather an exploration. As you went through each section, I could see how you were approaching various problems and learned a lot about Racket in the process. I would love to see more of this style of post.

artyomkazak4• 12 years ago

Of course I couldn't summarize Racket in a page – I don't know it! And there's so much to learn about it that I could probably write half a hundred posts of this length and still consider myself a beginner.

mahmud• 12 years ago

That was intellectually honest. Good read.

Strilanc• 12 years ago

Is this... a Let's Play of learning a programming language? Because it's surprisingly effective. I learned and I was entertained.

gamegoblin• 12 years ago

I would definitely watch a video series in which an experienced and talented programmer tried out various programming languages for an hour and gave first impressions, comparisons, etc as they hacked something together during the video.

beefsack• 12 years ago

The idea of a twitch.tv stream sounds interesting, with viewers throwing small problems at the coder to solve as they fumble around with a new language.

comex• 12 years ago

One note:

Racket's default IDE is better than GHCi and probably on par with Emacs (you almost certainly can configure Emacs to be better than anything, but it's not trivial and people don't bother, while DrRacket provides autocompletion and documentation out of the box).

Last I used it (a few years ago), DrRacket was very laggy, so I would find it very hard to use for a serious project. YMMV, maybe it's improved.

Crito2• 12 years ago

I love Racket but I have only ever had the same experience with DrRacket. I don't know what it is trying to do, but it brings my modest laptop to its knees.

codygman• 12 years ago

Interesting... I've never had any problems with DrRacket. What qualifies as a "modest laptop"?

anaphor5• 12 years ago

Yeah DrRacket is fairly slow unless you have a powerful computer. I recommend just using a text editor and making use of XREPL, see: http://docs.racket-lang.org/xrepl/index.html?q=

tl;dr, open up the normal repl by typing "racket" and then type (require xrepl) and then ,install! (leading comma denotes an xrepl command).

Then when you want to interact with a file you can do racket -i $file to interact with it using xrepl.

If you're wondering why this isn't just the default, I think it has to do with the readline license.

brudgers8• 12 years ago

     racket -il xrepl

Will launch Racket with already xrepl loaded.

brudgers8• 12 years ago

I find DrRacket sufficiently fast and sufficiently frustrating.

It's very useful for interactive debugging but dependent on the mouse and many Emacs key combinations simply cannot be mapped because of it's CUA interface...and so far as I can tell there is no key-combination that switches focus between the REPL pane and the Editor pane short of closing the other pane.

The syntax analysis gets to be a bit much too.

On the other hand, that's just the price of an IDE over a text editor, and for a batteries included IDE, it's pretty good even if I wish that the effort would have been put into Emacs support while knowing that doing so would not meet the needs of the PLT group's target audience of students.

anaphor5• 12 years ago

by default ctrl+f6 will switch focus. You can remap that to something more convenient though (it's called shift-focus).

brvs• 12 years ago

I think you can switch panes with C-x C-o, same as the Emacs combo.

laichzeit02• 12 years ago

Try the Geiser plugin for Emacs. It allows you to connect to the Racket REPL (either it starts a new instance of Racket, or it can connect to a socket/port).

I'm a Vim user and went through elaborate pains to get Emacs working almost like Vim just so I could go through SICP this way.

vitalique2• 12 years ago

Could you please outline your final setup besides using Geiser? I also come from Vim-land, have almost zero experience with Emacs and already understood that, to learn SICP, setting up and learning Emacs is going to be easier than setting up Vim for the task.

JimmyM3• 12 years ago

I actually found DrRacket very fast and Emacs very slow, on every computer I've tried them on. Why might this be?

sjolsen• 12 years ago

Emacs Lisp is interpreted (or byte-interpreted), and (GNU) Emacs is written almost exclusively in it, so startup can be dog-slow. Once it's up and running, though, I've always found it pretty snappy.

agumonkey• 12 years ago

I remember DrScheme as it was called before, it was snappy even on old amd duron boxes. DrRacket is very heavy. As other suggested, emacs+geiser gets you quite far. Maybe less nood friendly, because well emacs, no fancy gui artefacts (arrows and such).

SmileyKeith• 12 years ago

I love the play by play of exactly what you're thinking as you're doing something new. I find them quite informative.

brudgers8• 12 years ago

As others have said, this does justice to the idea of actually learning a new language...or perhaps because it is Racket a new family or ecosystem of languages. Anyway, if you're still curious about pairs verus lists and why anyone would use dotted pairs, I like to think about it as where Lisps show that they are from the age when running close to the metal was a given.

And it all goes back to car and cdr and the fact that they are (or rather were) embedded assembly language and there to give raw access to Lisp's linked memory model (as opposed to the sequential memory model of Fortran). A dotted pair has two efficiency advantages over a proper list and both stem from the fact that the last cell of the last pair of a proper list contains 'nil (or 'null in Racket).

Storing two values in a proper list requires two cons cells - the first with the first value and a pointer to the second cons cell and a second cons cell containing the second value and a null pointer. In contrast, a dotted pair holds two values in a single cons cell - halving the memory requirement.

The second advantage is that when there are only two values there's no need to walk the list and test for 'null (or 'nil) on the cdr. This saves an instruction step.

Philosophically, dotted pairs allow for car and cdr to be used symmetrically. Calling cdr on a dotted pair returns the second value directly just as calling car on any list returns the first value directly. Lastly, one of the things that is awesome about Lisp is the way in which lists can model data structures, and in the case of a dotted pairs their efficiencies are available to all those structures which consist of or rely on paired values.

Of course, this may be obvious and on a machine with 10+ GB of RAM not really applicable, but I find it fun to think about anyway.

Sean-Der2• 12 years ago

In some cases it makes more sense to store things as an a-list.

A good example would be simple key->value pairs. When working with Hunchentoot it represents HTTP Headers and form POSTs as a-lists. It would be easier to use a hash table though.

brudgers8• 12 years ago

I probably shouldn't have focused on data structures when talking about dotted pairs, but some days it's just hard to be a Lisp head...

     > (define (f g)
            ((car g)(cdr g)))

     > (define my-val (cons sqrt 4))

     > (f my-val) 
     4

...and go down the rabbit hole where code and data merge.

ANTSANTS14• 12 years ago

My question is, given the cons pair is not a meaningful primitive datatype to modern CPUs (can't fit in a register unless you're using 32 bit atoms on a 64 bit CPU, the individual cells cannot be meaningfully manipulated while packed into a single register even in that case...), is there a good reason to use an unrestricted pair/2-tuple/2 element vector for the sexp representation? Would it be "wrong" to remove dotted pair notation and make sexps a restricted type whose cdr could only be another pair or the empty list? You'd have to give up alists, but those would probably be better served by doing as Clojure does and introducing a hash table syntax.

Other than alists, simplifying the implementation[1], and tradition, I can't think of a good reason to keep improper lists and dotted pair notation around. They aren't really that useful, confuse newcomers, and encourage the use of inefficient data structures. I haven't written much Lisp, but when I see a dotted pair (usually in the context of an alist or some hideous approximation of a struct[2]), it comes across as a "code smell" to me, like "this person is taking SICP too literally."

[1] You pay for extra reader syntax, but gain uniformity in your treatment of the car and cdr cells. On the other hand, maybe you could optimize the cdr cell a bit if it only needed to address pairs and not arbitrary atoms.

[2]

  ;; barfage
  (define (make-thing a b c) (cons a (cons b c))) ; barf
  (define (thing-field-a x) (car x))
  (define (thing-field-b x) (cadr x))
  (define (thing-field-c x) (cddr x)) ; more barf

Sean-Der2• 12 years ago

I come from a background using Common Lisp for system and web development so I may see things differently than people who were introduced to it academically. Your code looks great, mine just needed to compile :)

The cons pair is a a really powerful primitive data structure, it is the linked list of Lisp. You can build a lot of powerful structures given this great base. I really don't it matters what architecture your running on.

Do they really confuse people new to Lisp? car+cdr is a pretty simple concept, when talking to new Lispers they usually don't complain about this.

Hash Tables are part of the Common Lisp Hyperspec so that is a non issue, they have been first class citizens since before Clojure existed (and are nicely integrated into things like loop)

anaphor5• 12 years ago

It has pedagogical value to define things in terms of a very small kernel language. You will find things like alists in fairly advanced books on lisp (e.g. Lisp In Small Pieces) simply because it reduces the number of extra concepts you need to explain. It's assumed that the reader can figure out how to make the code cleaner and more idiomatic as long as they understand the ideas being presented.

Also I have made use of improper lists in my code, usually when I need to do something with multiple values and I don't want to mess with multiple return values, or if I just want to create a list of tuples for some reason and don't feel like defining an actual struct (can't think of a good example right now...)

brudgers8• 12 years ago

Going a little Abelson&Sussman, the utility of cons persists because it is a powerful abstraction. Fitting into registers was, as a scholastic might say, an as accidental feature as the input line voltage of a toaster [110 @ 60Hz makes things easier in this part of the world but isn't intrinsic to making crisp English muffins].

cons is useful for dealing with linked memory structures, including singlely linked lists and particularly singly linked lists where the stored value in each list element is a pointer because it abstracts over all the pointers. Writing code to process and manipulate and pass pointers is idiomatic in C. Using pointers is idiomatic Lisp.

Your barfing code shows why cdr and car persist. They are also powerful abstractions due to their rules of combination and probably because their rules of combination aren't constrained by a bias toward English language. There ain't no synonyms for "caddr" and "cdddr" in English or Python.

The idea that lists should be everywhere replaced by structs is assembly in any language thinking (also known as C). Lists provide a standard interface. Each struct definition creates a new data type.

It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures. Alan J. Perlis, Epigram 9.

charlieflowers• 12 years ago

Web apps are a hack on a hack, yes. But it's kind of ironic he hates Javascript so much when Javascript is a pretty cool programming language heavily influenced by Scheme, which is awfully similar to Racket.

But hey, I like people who call it like they see it, and there certainly are some drawbacks to Javascript too.

ktg• 12 years ago

Javascript is a pretty cool programming language heavily influenced by Scheme. -> I couldn't agree with you more.

There is a Lisp-to-JS compiler (ParenJS). https://bitbucket.org/ktg/parenjs

derengel• 12 years ago

A friend of a friend has considerably code in Scheme, Common Lisp and Clojure, when you ask him which is the true Lisp, guess what will he answer? Haskell!

Haskell does really create a big impact on some developers.

Just an anecdote ;)

dllthomas3• 12 years ago

I think it can't be "the true Lisp" without cleaner macros. Of course, that doesn't stop Haskell from being a great Haskell.

TuringTest• 12 years ago

Haskell is the algebra of programming - the way to handle code expressions as Immutable Truths.

I suppose that makes Lisp the Principia Mathematica.

Tyr42• 12 years ago

I do prefer Racket macros to Template Haskell, but you can do some of the same kind of things in Template Haskell. Go ahead and play with it for it for a bit.

Mostly, you need to have the data-structure it defines for the parse tree, and it's harder to convert than syntax->datum. Also there's the Q monad, to generate new safe names. But it works pretty well.

nnq2• 12 years ago

This sums up quite a lot about Lisps in general. I'm amazed OP got so fast to this "insight" :)

    (And this is probably Lisp's greatest weakness as well – with this level of
    possible diversity, everyone has to use the “common lowest denominator”
    simply because nobody can agree on what alternative syntax / library / etc.
    is better and should be used.)

    Off-topic: it's not enough to give everyone opportunity to improve the
    language; you have to choose the winners and promote them heavily. The rules
    of free market don't work here; people won't use the best thing, they'll use
    the one which is available out of the box and which is used by their peers.

grn• 12 years ago

That's very true and I think that it's related to the topic of Rich Hickey's talk Simple Made Easy [1].

Maybe what we need is to study the economics of software and come up with a system in which market outcome is promotion of good libraries. I think that the social/economic dynamics of software development play a huge role in building a successful product, both free and commercial. Has anyone studied the subject in greater detail?

[1] http://www.infoq.com/presentations/Simple-Made-Easy

pavelludiq2• 12 years ago

As a lisper, I can say that this insight is very true, but it is still just a simplification. Most lisps deal with it in different ways.

In the scheme world, the way they deal with this is by wasting a decade on making decisions about the language that should have been done in the 80s. The result is that scheme essentially split into scheme and racket. Now we have an awesome language and a nice little ecosystem thats good for teaching and research, and possibly even real work(tm). Classic scheme unfortunately is fragmented into implementations who all do things slightly differently and occupy their own niches.

In the clojure world, they have a) a BDFL who sets the course of the language. b) A very strong core community of very smart people who managed to build a nice culture based on common ideas about software and design.

In the common lisp world, because we have a very high-quality standard, implementations are almost completely compatible. Compatibility libraries make it easy to write very portable code, avoiding the scheme problem. At the same time implementations are free to experiment. The other problem of everybody developing their own little universe tends to be rare. Because common lisp is so old, we have a long history and traditions that guide future design, but don't constrict it. There is a subtle balance here. We have a lot of old examples to learn from, but we are not locked in by too many bad old decisions(not always the case, but good enough in practice).

A few examples where this does not work include utility libraries and things like json libraries, libraries for outputing html etc. Since we don't have a BDFL we are left to figure things out amongst our selves and sometimes, like with utility libraries(there are dozens such, which is ridiculus) it doesn't work. In other cases, it works very well, for example quicklisp, ASDF, bordeaux-threads, closer-mop, hunchentoot etc. are either de-facto standards, or sufficiently popular to be a very good default. As with clojure, there are a lot of common ideas about what is good design in the community, we have a lot of examples to learn from, as I mentioned.

In the end, at least in the case of common lisp and clojure, I see it as an advantage to have this "level of possible diversity", it's what has kept lisp alive for 50+ years! The fact that lisp can adopt to each new era of software development philosophy is a great reason to study it. It will be with us for many more decades because of this.

oblio• 12 years ago

At this point we can safely say that any programming language will be with us for many decades. Cobol (http://en.wikipedia.org/wiki/Cobol#COBOL_20XX), Fortran (http://en.wikipedia.org/wiki/Fortran#Fortran_2015), Basic (http://en.wikipedia.org/wiki/Visual_Basic_.NET#2013_.28VB_12...) are still evolving. Heck, Python is already 23 years old and I don't see it going anywhere. I'm not even going to talk about the ubiquitous C/C++ or Java, as they'll probably be around long after we're dead.

Adaption is neat, but I don't see this argument as being a very solid argument in favor of Lisp - it's just the norm.

PeterisP• 12 years ago

To me, "almost completely compatible" sounds similar to "just a tiny bit pregnant". In practice, either it is compatible, or it isn't.

artyomkazak4• 12 years ago

I think this was a cached thought – a year ago I was reading a bit about Lisp and probably had stumbled upon what is known as the Lisp Curse.

Dewie2• 12 years ago

I dream of a modular language in which languages, or dialects, can be built from a small base language, which can then be extended, and so on. Of the languages that I've seen, Racket looks the most promising. Forth might be good for this, too, but to build large hierarchies of languages seems the antithesis of Forth - or at least, Chuck Moore's - philosophy.

On the other hand, such a language might just end up as an incredibly fragmented mess of different languages, with little interoperability between languages - some one makes a 'typed' version of the language, another takes that version and tunes it just enough for it to be incompatible with the original version and, in turn, all languages that are built on top of that original typed language, and so on.

Maybe incredible modularity is fundamentally at odds with (social) interoperability.

dmytrish3• 12 years ago

It's ironic that Haskell is such a language: it grows from a tight, small core into larger and greater abilities as you learn it even without using its extensions.

I agree that Common Lisp a very powerful language, but I can't live with all that power uncontrollably thrown on me. Common Lisp grossly lacks self-discipline and self-limitation when it's needed.

rlander• 12 years ago

Maybe you dream of Rebol?

[http://www.rebol.com/rebolsteps.html]

toolslive• 12 years ago

he will be amazed when he discovers custodians. http://docs.racket-lang.org/reference/eval-model.html#%28par...

klibertp• 12 years ago

There are many cool features that Racket has out of the box, like very nice module system, delimited continuations, objects and classes and of course macros (both hygienic define-syntax-rule, syntax-case and unhygienic defmacro) and more.

But if I had to show one feature of Racked to make someone amazed, it wouldn't be any of those. It would be a simple program composed of a couple of files, and every file would start with different #lang. Like #lang racket, #lang lazy, #lang typed/racket, #lang datalog.

It's sufficiently mind-blowing that there are this many languages on top of Racket, but the real "killer app" is how seamlessly they integrate with each other.

The next thing I'd show would probably be Danny Yoo tutorial on how you can create even more languages like this: http://hashcollision.org/brainfudge/

nextos2• 12 years ago

It's almost like a practical Mozart/Oz with all Lisp awesomeness. CTM shows how programming with many different paradigms can be extremely powerful.

JimmyM3• 12 years ago

This is how I usually implemented quicksort in Racket:

    (define (quicksort xs)
    (if (null? xs)
    xs
    (let* 
        ([hd (car xs)] 
         [tail (cdr xs)]
         [smaller (filter (lambda (x) (< x hd)) tail)]
         [bigger (filter (lambda (x) (>= x hd)) tail)])
      (append (quicksort smaller) (list hd) (quicksort bigger))))

It's great to see a hugely superior implementation, and I love that people are writing about and using Racket like this because the more people do that the more resources there will be for people like me to learn from.

nextos2• 12 years ago

I love Scheme. And I love Clojure, which is IMHO Scheme plus some great ideas from Haskell.

I regret there's no Scheme or Clojure running on LLVM, which I think is a much better platform than the JVM. Julia, that resembles Dylan (another Lisp), is the perfect example.

saosebastiao• 12 years ago

I too wish there was such a thing as a JIT compiled Clojure on LLVM. The JVM is amazing but it only seems to be amazing for long running processes. LLVM, IMO, is far more versatile in its amazingness.

pjmlp• 12 years ago

There was an attempt at it, https://github.com/halgari/clojure-metal

ihnorton• 12 years ago

Not sure what Lisp family it compares to, but there is Hylas:

https://github.com/eudoxia0/Hylas-Lisp

gambogi• 12 years ago

"Someone who knows Haskell learns some Racket"

"Tonight at 11: this rose gardener learns to plant tulips"

artyomkazak4• 12 years ago

Which is exactly why I was very surprised when it got posted to Reddit and wasn't immediately downvoted.

kenko• 12 years ago

It seems as if several of the author's problems come, oddly for someone who's used both strict (Pascal) and non-strict (Haskell) langauges, from being confused about Racket's strictness. Why is time a special form? Because otherwise (time (expensive)) would just get the result of (expensive). Why doesn't (list 1 (2 3) 4) work? Because list isn't a special form, it's a function. Why doesn't quote turn '(list 1 2 3) into '(1 2 3)? (Well, this one isn't about evaluation order, admittedly.) Because if it did it ... wouldn't be quote.

artyomkazak4• 12 years ago

Pascal is strict, but it still has stuff like “move(var1, var2)”, out parameters, etc., so it's also call-by-reference.

I didn't know at the time that Racket was call-by-value.

Quote was confusing at first, yes.

A Haskell Programmer Tries to Learn Racket

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