A Look at the Design of Lua
cacm.acm.org
cacm.acm.org
He then explained this "dictatorial" behavior is what allowed him to keep the implementation simple and concise over the years. At the time he boasted about the source code being less than 8K LOC, though it has likely increased in recent versions. (I think it was around version 3.) I'd recommend taking a look at the source code, it's truly a C masterpiece.
Prof. Ierusalimschy's was one of the most interesting seminars in my first year. His passion is apparent in the way he talks about Lua's history and current development. Unfortunately I haven't taken any courses with him
As a side note, it's nice to see folks from around here on HN
- Before Lua 5.3 there was no integer type, this makes a lot of things harder than needed in programming, unless you just write high level code.
- Lua trivially departs from standard syntax like ==, !=, zero-based indexes, without good reasons, creating a general feeling of confusion.
- There was an odd idea about what to include by default and what was optional. The lack by default of bit operations makes the language always in need of a trivial library.
- Tables as a single data structure are not ideal for many tasks. Especially the dualism between tables that are indexed by sequential numbers and tables acting as maps. It's a lot more kind to your users to give up with the solely academical ideal of "just one data structure", and give programmers at least an ordered and a map data type, or at least come up with something better than that. Lisp attempt at doing most things with lists was much more successful and clean.
- The stack-based C API is not comfortable to use.
I could continue to be honest, for instance by default you can't type an expression in the REPL and see the value returned. However when the task at hand is to write small scripts for a larger system, the implementation of Lua offers big enough advantages to make it a worthy choice.
Despite its warts lua still feels like a better (imperative, statement-based) scheme than scheme to me. What scheme offers a similar combination of speed and expressiveness for the same conceptual and file-size weight as lua(jit)?
Wrt to repl: the torch7 repl is quite serviceable, so it's worth giving it a try even if you're not into deep learning.
That would have to be quite the subset. The Ruby parser alone is almost 12kLOC. I've implemented entire languages in 1/10th that.
Sounds great, but:
$ luarocks install trepl
Error: No results matching query were found.
> Torch is not in active developement
Is there a maintained torch7 repl somewhere?
Maybe Pawn or NekoVM.
https://nekovm.org/doc/lua/ https://github.com/compuphase/pawnv Also, everybody loves benchmarks: https://github.com/r-lyeh-archived/scriptorium
The default numeric type (double float) can precisely represent integers up to 2^53. That's ample for most of my purposes. You can even fit x86-64 pointers into them.
Syntax doesn't match C but that doesn't bother me because I'm used to other languages already e.g. Erlang that uses different operators and one-based indexing.
Bit operations are always there in LuaJIT.
The C API does seem awkward to me too but it's superceded by the lovely FFI in LuaJIT.
> The stack-based C API is not comfortable to use.
What is so uncomfortable about it? I think it's absolutely fantastic. There's nothing you can't do with it, and if you really want a heavyweight "magic" binding library you can do that on top of it. But you'll find even then you occasionally need to fall back to the "raw" API.
Another problem I've with the stack API is that it's insecure by default. If you push too many things it will result in a C stack overflow. I'm not sure how much performance this gives, I mean, the inability to grow the stack automatically looks like an optimization matter... But at least, panic when we reach the max stack instead of smashing the C stack.
There are still quite a few places in the code though, where some complex stack operation is happening and each line of C/ObjC is surrounded by a lot of comments that describe the expected state of the stack at each step, and there have been a lot of situations where I've ended up having to sketch the stack on paper as I'm reading code, to figure out why something isn't working.
So, I think I'd say that the C API is not comfortable to use, but it's also not very complicated. It's somehow managed to be simple, but hard, if that makes any sense.
Edit: If anyone cares, our Lua abstraction is all written in ObjC and is called LuaSkin. It lives in the Hammerspoon git repo, but doesn't actually depend on Hammerspoon at all, so could be extracted and used by others (it's MIT licensed). The API docs are: http://www.hammerspoon.org/docs/LuaSkin/Classes/LuaSkin/inde...
And this is quite fair. Those are fundamental qualities of a new programming language.
Having taught programming to many people outside of the programming field, one of the biggest sticking points I have found they face early on is calling the 1st thing the 0th thing, instead of just the 1st thing which is what they've been doing their whole lives. This leaves them with the general feeling that programming as a practice is nonsensical and arbitrary (and they're not wrong). It can turn off a lot of people as they grow frustrated by constant off-by-one errors, which tooling doesn't do much to catch.
If Lua wants to be a language for non programmers, 1 based indexing is a good choice imo.
I'm just telling you what hundreds of people have told me. They expect the first thing to be #1. Their words. I dont see how you can call their own experiences invalid.
Your dismissive attitude is another reason why so many non programmers have trouble learning programming.
>> "They expect the first thing to be #1".
I expect the laws to be easily understandable by a layman. Should I become a law-making advisor, then?
I believe everyone can be taught to program, and the choice of language, semantics, and syntax has a profound effect on how far people can get, and what frustrations they face.
There are people out there with 0 formal training who run entire businesses on Excel, the most widely used programming language bar none (it's notable that in Excel, rows start at 1 and not 0. There is a reason for this). Ask a 7 year old to use C and they're not going to get very far. Give a 7 year old Logo, and they'll be writing programs with very little instruction, with results I've seen college freshmen struggle with.
I teach a summer robotics program to middle schoolers. We used to teach it in C++ because that's what the SDK came written in. In this mode, we spent most of the time getting them to think like the compiler, teaching them about memory layout, allocation, compiling, headers, preprocessors, etc. because they constantly ran into frustrations due to the design choices of C++. They never left the session with a firm understanding and confidence around programming because they spent all their time trying to build a model from scratch in their head without any relation to their own world.
Then we switched to Matlab. With one uniform data structure, a REPL, 1-based indexing, etc. they were much more comfortable, and they were able to make the robots do amazing things for their age. The most impressive thing I've seen is making a robot choir through writing a distributed protocol to synchronize the robots' notes. They were able to do this because the language, Matlab, got out of their way, which allowed them to focus on the task and relate it back to something they knew very well: music.
All I'm saying is this attitude of "Oh, you don't understand this thing we've built and these arbitrary limitations frustrate you, therefore you shouldn't even try it in the first place" is just toxic, given the evidence I've seen that people can learn and do amazing things if we give them a fighting chance.
Required reading on this subject: https://www.amazon.com/Mindstorms-Children-Computers-Powerfu...
I have a different view.
Lua tables are the foundation for just about any conceivable data structure in CS. While you can do a lot with raw tables in Lua, you can also use them to build all kinds of things on top of them, like b-trees. Or an object system (which is a popular hobby among Lua aficionados).
There's a limit to what can and should be built into any base language. Trying to wedge in more container types can cause a bit of difficulty, in my opinion. Python is the classic example here, where you have tuples using parens, arrays using square brackets, and dictionaries using curly brackets. At some level that is clever, but at another level it is a cause of confusion.
Tables are a basic mechanism for implementing any data structure. That is a qualitatively different statement from saying that tables can replace any data structure. If you need semantics different from what tables immediately provide, you'll need to implement the desired data structure yourself -- but Lua gives you good tools to do that.
> Maybe there’s a better way I don’t know?
You can use `for i, v in ipairs(arr) do ... end` to iterate over an array without worrying about "how far" to iterate. The `ipairs` iterator will determine when it hits the end of the array.
My favorite example are arrays in Lua: They are hashtables, but not quite (in the implementation, every hashtable has a separate array region). They look like hashtables, but not quite (there's syntactic sugar to help dealing with them). You can use hashtable-functions on them, but they don't quite work (which is why there are special functions for when you want to treat a hashtable as an array). Hashtables are great for unordered maps and sets, but they're a crappy replacement for ordered sequences.
> Python is the classic example here, where you have tuples using parens, arrays using square brackets, and dictionaries using curly brackets. At some level that is clever, but at another level it is a cause of confusion.
If that confuses you, then the source of the confusion is you not having a clear understanding of the intended semantics of your code or datastructure. Mixing all of that into a single type won't help here.
Tables + metatables mean that pretty much any structure you want is available. Single Inheritance + Interfaces, Multiple Inheritance, Component Based Design are all things I've seen in the wild on shipped products with Lua.
It's a fantastic 'orchestration' language. Coroutines were also invaluable. We used them extensively to script AI behaviors. Our designers(yes, not developers) would write them with "go to X location", yield, "search for players", yield, etc. Was a really compact way to build a FSM that they could understand.
Wasn't the idea to only use lua as a high level scripting language, and drop down into C(++) if you needed to go low level?
I still think it contains some neat ideas and concepts, even though I would never actually use it for something practical.
Having written a ton of networking code in Lua I can tell it has a lot of design defects that most other programming languages have avoided. Especially the deeply embedded one-based indexing and lack of a separate integer type (chars are strings, ints are floats) make it wearing to type any code that has to parse any binary data. Even bit manipulation requires going through the FFI. Considering that Lua is often touted as the optimal lightweight solution in small embedded systems, these features are must-haves.
The builtin string pattern matching library attempts to mimic regular expressions, but bites the user in the leg every time they attempt to use it for anything remotely regex-y. Unfortunately most usual string manipulation seems to revolve around them and the string.gsub function.
The inconvenient string library is also largely irrelevant. The developers call their language eight-bit transparent which in reality means that the programmer needs a separate Unicode library, rendering the whole standard string library mostly useless. One cannot even format UTF-8 text, because the string library doesn't differentiate between characters and bytes.
The official documentation mostly revolves around C bindings. The actual Lua language documentation is provided by another web site that looks like it has been written by an attention-deficit child. Instead of getting to the point, the articles often first provide a list of ways on how not to implement things, or they are actually benchmarks of fifteen different ways to call the standard library to get the same effect. Sometimes, the provided code does not even work – for example, the given XML parser code crashes when it hits one of the error paths.
The small runtime and fast VM do not really matter when the language itself is lacking and requires a metric ton of external libraries to achieve even the simplest things that are possible in standard C and Rust, which provide the same level of performance and better type safety.
Edit: If you have a device with enough computing power to run a scripting language interpreter, you can use Python in most cases.
Lua is very dynamic, easy to code for (syntactical quirks aside, I'm talking from a "cognitive load" standpoint) while C and especially Rust are a lot more static, require more careful coding but can result in faster and, at least in the case of Rust, more robust code.
Lua is the type of language you embed in your C app to make it configurable.
That's not a fair comparison. A large chunk of the cognitive load comes from the awkward syntax and other design decisions that stem from it.
>Lua is the type of language you embed in your C app to make it configurable.
Situations where configuration files aren't sophisticated enough but a Python interpreter is too heavy are few and far between.
>Situations where configuration files aren't sophisticated enough but a Python interpreter is too heavy are few and far between.
That's not the point I was making and I'm not trying to get into a language war between Lua and Python, I have no horse in that race.
I strongly disagree. The unfortunate design decision of folding arrays into hashtables forces you to be very careful when you conceptually need a sequential list, because if you store a null value in it, you cut your list in half. Ooops.
An array is the most basic, simplest, most useful non-scalar datatype there is, and Lua bungles it.
I've switched to using Wren for my new projets. Despite not being as mature as lua (you may have to add some functionalities yourself):
* the syntax is much nicer.
* it's simpler/cleaner to embed.
* it's (allegedly) faster if you are running on a platform where it's forbidden to JIT (e.g. iOS).
* Classes in Lua are a hack, and consequently the syntax for them is terrible.
* Using "end" instead of "}". That decreases readability.
* no "+=" or "++" operators.
That's already reason enough for me not to use it. One based indexing caused me so many headaches in the past in Mathematica...
As a matter of fact, I had the exact same argument in a Julia thread (modulos don't work, polynomial accesses don't work).
It honked off a whole bunch of people who've never had to do any of these things for a living and therefore considered them edge cases.
Additionally, for LUA, being one-based while trying to claim it's the scripting language for C inter-operability is quite preposterous.
In the same ways that simple for loops "don't work" because we need to e.g. check if i < length - 1 to know if we're at the last element...
It's not. You're asking new learners to overcome a great deal of intuition when already attempting to learn a mind-bending thing like programming. I've taught C++ and Matlab side by side to freshmen in university. They learn C++ first and encounter all kinds of off-by-one errors the compiler doesn't help them catch. When they get to Matlab, the universal sentiment I've found is "wow, this makes so much more sense"
For new learners, 0 indexing seems like such a pointless frustration with an obvious solution. It can be a needless roadblock for people otherwise excited to learn.
Same goes for indexing, you could write some functions like idx2(x, y, width, height), idx3(x, y, z, width, height, depth) that would compute the 1d index for you instead of using y*width+x (or the equivalent form adjusted for 1-based indexing) like you normally would.
> Even bit manipulation requires going through the FFI
This, and some of the other things, have not been true for years.
make generic local
> lack of a separate integer type (chars are strings, ints are floats)
Lua 5.3 introduced integer types. [1]
> Even bit manipulation requires going through the FFI.
LuaJIT includes a bit manipulation library, but its FFI acceleration is optional. Also, Lua 5.3 introduced bitwise operators. [1]
> One cannot even format UTF-8 text
Lua 5.3 introduced "basic utf-8 support" [1] although I am not sure to what extent.
> The official documentation mostly revolves around C bindings. The actual Lua language documentation is provided by another web site that looks like it has been written by an attention-deficit child
Again, I suspect you are criticizing LuaJIT. The actual Lua documentation [2] has never let me down.
Nope, plain old Lua 5.1 which is still the newest one can get on many platforms. You're stuck with what you have, not what was released yesterday.
>The actual Lua documentation has never let me down.
I read the document you linked and found the documentation lacking on anything but basic syntax and C bindings (the chapter on C API comes before the Lua standard library, btw). The standard library function documentation underspecifies parameter types and both return value types and numbers.
I find the Lua Short Reference [1] much more accessible than the official documentation. It has the very same information in a much more readable format.
>Lua 5.3 introduced "basic utf-8 support"
Looking at the documentation you linked, the Unicode support does not integrate with the string library. Walking a UTF-8 string manually character-by-character has never been difficult and Lua 5.3's support doesn't seem to address any other use cases.
[1] http://lua-users.org/files/wiki_insecure/users/thomasl/luare...
Most devs aren't interested in the additional burden of maintaining and crawling through the code when an edge case pops up.
5.3 where all this are solved is the most recent stable version -- not what most people have used for the entire history of Lua (and not default in all distros).
One based indexing is just a design choice, while it complicates interoperation, I find it justified as Lua tables are actually hash tables, so it would be weird to model it upon memory offsets. It reminds me that I am only dealing with a hashmap with integers as keys.
Bitwise and UTF-8 string operations are lacking out of the box, but these are arguably too specialized to be expected in a general scripting language. The patterns are a little underpowered compared to other languages, but it is still quite useful. I suggest looking into LPEG for more complicated operations. Lua 5.3 do have some functions to deal with UTF-8 codepoints.
Also, regarding Unicode, I'd rather the PL provide only operations on bytes, and let me decide what "characters" are to be represented. Nearly all PL providing some Unicode facilities fail in different ways, just let me deal with ICU myself if I really need Unicode. Also it is a royal pain in the butt to deal with different encodings, with a language having special "characters" and "strings" constructs.
I don't understand the complaint on documentation. It is one of the most practical and clear technical writing that I have seen, if a little terse. Perhaps you mistook the wiki as the main document? (The Lua language manual is an one-page HTML page.)
If this is true, and I actually agree with you, then where is Lua actually better than an alternative?
And, while I don't share the specific points of the parent poster, I experienced similar issues with Lua. I found that while the Lua core language itself is small, I had to compile in so much extra stuff to make it useful that it wasn't actually small anymore.
And, once you get large enough that you start demanding big ARM Cortex M4 microcontrollers, Python is now in your scope.
I think the idea is that most functionality is meant to be provided by the host program. If you want a standalone scripting language, then Lua probably isn't for you.
There are entire games built around modding via lua such as gary's mod which similar to a web browser has to download random code from a server. Then there are mods like computercraft/opencomputers for minecraft in which direct file access to the host doesn't make any sense at all because every computer has it's own filesystem.
I just looked up Python's sandboxing capabilities and I can't find anything. All I see is answers like [0] that suggest that it's not trivial.
What about other implementations like pypy that claim to have a sandbox? [1] I can see lots of warnings like "This is not actively maintained."
The lack of mature sandboxing for python makes it impossible to use for the usecases I've described above.
[0] https://stackoverflow.com/questions/3068139/how-can-i-sandbo... [1] http://doc.pypy.org/en/latest/sandbox.html
Why is Lua an oft-recommended programming language for embedded development if one is not allowed to form opinions on the language?
>so it would be weird to model it upon memory offsets
Why does the language provide table constructors {1, 2, 3} that do one-based indexing then? Why is there a table length operator (#) that works on one-based indexes? Why does ipairs work with one-based indexes? A sequential data type (array, list, for some quirky reason named "tables" in lua) is one of the most basic data structures of a programming language. If Lua is supposed to be a scripting language, why should a programmer care about the underlying implementation?
>Bitwise and UTF-8 string operations are lacking out of the box, but these are arguably too specialized to be expected in a general scripting language.
Is Lua a toy or a tool?
>Lua 5.3 do have some functions to deal with UTF-8 codepoints
I welcome you to the real world, where 5.1 is still the latest available release available on too many platforms.
>Perhaps you mistook the wiki as the main document?
Lua-users.org turns up as the first result when you google for documentation.
I have never heard anyone recommend Lua for embedded development. It's an embeddable language in the sense that you can easily embed the entire interpreter in a larger application and extend it. That it happens to be relatively small and easy on memory is a bonus, not a reason to believe that it's a great systems programming language.
I'm not at all surprised that it disappointed you as a language for low level networking code. Most Lua success stories are about its use as a high level glue/scripting/configuration language, letting the application handle the low level code via an API.
The runtime is small and, all things considered, it's very fast. While I never got to a place where I was writing low-level networking code with it, when I was still in embedded I did use it for a number of tasks that it was perhaps not quite perfectly suited for because of it's characteristics. I'm no longer in embedded, but I can easily imagine having pushed that idea further with projects like LuaJIT showing up in more recent years.
The GP obviously ran into some obstacles using Lua 5.1 for systems programming, though, and my point is that his experience probably doesn't reflect the overall utility of the language as much as it presents a case of "the wrong tool for the job".
One based indexing isn't just about memory offsets or getting used to it, it makes lots of things a nightmare. Like index-math that involves the modulo operator, which will result in zero values, which are invalid for 1-based indexing. Or turning a 2D or 3D index into a 1D index, which now requires completely unnecessary additions or subtractions of 1s. And other index magic that I frequently need for computer graphics and number crunching.
Also the documentation provided by lua.org is quite accessible: https://www.lua.org/manual/5.3
What I'd really like is stdlib to provide a Buffer type, as opposed to having to use a table of integers which then gets pushed into a string with chunked calls to string.char(table.unpack(buf, n, n+4096))
Example of what I'm complaining about: https://github.com/serprex/luwa/blob/master/rt/make.lua#L758
So all said I don't disagree with you: Lua can fall short, it doesn't have the community other languages have built up, & the community it has is rather fractured. Like LuaJIT making 5.2 what most call Lua, but also that being an extension language it's hard to upgrade without losing compatibility, so projects like Redis can't upgrade without deprecating 5.2 for a 5.3 version & making some method to signal 5.3 & then eventually removing 5.2 while packaging both in the interim
Other than that, as others pointed out, most of your complaints are addressed in 5.3.
This is such an unfair point. Lua has a single manual that covers the language, the standard library, and yes, it also covers C FFI (unsurprisingly for an extensibility / scripting language), but FFI actually comes after the language in the docs. And the manual is both very readable and very thorough where it talks about the language - it's quite easy to learn the whole thing just from it alone.
The "actual Lua language documentation" you refer to probably is the wiki? I agree it is crap.
By all means, stay away from Lua and use Python and Node for new projects; we like that competitive advantage.
I pretty much agree that Lua can survive such throughput, but I question whether Lua can survive the code complexity. I have written about Lua previously on [1] with a vocal conclsion that Lua cannot really handle a large code base (in the order of 10^5 lines), so I like to hear otherwise (hint: I hadn't). That's why...
> By all means, stay away from Lua and use Python and Node for new projects; [...]
...we have ultimately dropped (a heavy duty use of) Lua from all new projects. C# seems to suit our needs (or any other statically & strongly typed languages---obviously excluding C/C++---would probably do).
We have shipped and maintain a series of games built on progressive iterations of the same codebase; we have on the order of 200 KLOCs of Lua in the common "engine" code and tooling, and 200-400 KLOCs additional game-specific code per game. We tend to hit our milestones and performance targets on six platforms, with programmer quality of life way above the game industry "standards" (i.e. we do normal working hours).
Can things be better? Of course, they always can. But om our experience, large-scale use of Lua is not the disaster it usually is assumed/predicted to be.
For the context, we had about 100 and 200 KLOCs of Lua code for the server and client respectively. We had to use Lua 5.1 because there were not much tooling nor library around 5.2 or later at that time (pain point #1). We of course needed 64-bit integers and sticked to special string representations with some metatable hack, which itself was quite usable. There were several, often critical, bugs that were found to be fixed in 5.2+ but left out in 5.1 even though everyone knows that Lua 5.1 won't die out any sooner (pain point #2): the most critical one for us was the use of thread-unsafe `localtime` which made my jaw dropping. Also there was no clear migration path from 5.1 (AFAIK this holds for 5.2 as well) to later versions (pain point #3); we had to build many system around Lua's dynamism to deal with the complexity and, as you can guess, every minor release of Lua breaks enough dynamism to prevent easy migration.
Besides from this, every single library we have tried to use had a critical issue: luasocket plus luasec had spectacularily failed at correctly handling transport timeouts (pain point #4; we did use ASIO as a backend, we only needed them for some external services), luasocket alone had a very annoying and easy-to-mess API for every but simplest HTTP request (pain point #5; eventually we had to shell out to curl which was much, much better than any other Lua-based solution), dkjson had no control over empty arrays vs. empty objects which caused some interop problem; and so on and so on (I can't remember all of them). Ah, of course there are also shitty wikis but I dare not to describe them. We eventually had learned to avoid any external library or even snippet. I feel like that Lua actively encourages DIY mindset which is absurd for modern large-scale programming.
Have I mentioned that we had used Lua's dynamism to deal with the complexity? Well, we could only try. We had built our own version of unit testing system because, well, obviously Lua is built for embedding and standalone unit testing does not make sense when you have a custom environment, right? This one is acceptable, but the lack of coverage calculation is not (pain point #6). I had built a custom one, but that was waaaay slow that we couldn't use all the time (and I'm pretty sure that a right debugging API will immersely change the situation, but there is still none as of 5.3). Debugging was also abysmal (pain point #7), again Lua is built for embedding and standalone debugging experience does not make sense, right? We already knew and used MobDebug [1] which kinda worked but was brittle. We had eventually built a serious debugging tool (open-sourced!) that integrates to Visual Studio Code via Language Server Protocol. The remaining story goes much like this: there are no or only partial tooling around embedded context (supposedly the biggest use case of Lua), and we had wasted too much time to build ours including a type checker (!!!!) [2].
I do agree that Lua has some upsides as well. In fact, Lua greatly helped us to quickly build a functioning product from the scratch, and the ability to safely discard the whole state massively simplified the error recovery process (alluding Erlang's approach). I really, really want to like Lua because it seems the only one viable programming language with those charactistics. But my own experience says otherwise.
It seems the major difference is that we are fiercely NIH, or as you put it a bit more mildly, DIY. We very quickly switched to our own socket implementation, we built our own IDE based on lua's remdebug and Scintilla (this was way before Visual Studio Code was a thing), etc. I wouldn't attempt to use a "lua JSON library", we'd wrap an existing C JSON library and have it convert to/from Lua structures. At our scale and business model - lots of reuse across products, small programmer turnover - this is quite OK; I don't feel like wasting work when I do something like that, it's investing in the future.
How can you say that? The Lua documentation is on par with Kernighan and Ritchie.
The Lua community is small so every bit helps :)
Shameless Plug: https://Luadigest.immortalin.com
What drove me away from Lua is its philosophy of providing minimal tools in which it is possible, but never easy or convenient, to do work in various programming modalities. Polymorphism, namespaces and packages, arrays, unicode... these things all can be done, but require significant head-standing and in many cases a lot of boilerplate. Even proto-style OO, which you would imagine would be Lua's signature feature, involves lots of rigamarole compared to languages (like Newtonscript) where it is baked in and elegant.
I kept wanting Lua to pick a pony.
Throughout my usage of Lua, I've consistently gone back to Lisp, where I could change the language to make inconvenient things convenient when I needed to.
Off topic, but I've always thought that JavaScript and JSON would have been a lot better without the relatively artificial distinction between objects and arrays. Now that there's object shorthand and destructuring, this will never happen, but it was a nice thought for a while.
const a = [2,3,…]
a.prop = "hi"
(Also on my JS wish list: Killing the use of const for anything besides actual constants.)
You should be using const for everything besides variables that need to get re-assigned.
If you want a strongly typed language, go use C or Java and stop making JavaScript incomprehensible to all but the most pedantic developers.
That's not true in Java, C, Ruby, or Perl (with the 'constant' prag-module), not really true in C++ (unless you're careful), and . . . generally just isn't true in most languages.
While a few languages do add recursive immutability properties to their equivalent of 'const', most languages use the idea of a 'constant' only as a means of prohibiting name re-binding, not data modification. And even then, many languages that only prohibit const re-binding only do so in an optional (i.e. it's a warning) way.
Many of those same languages do support immutable data structures either out of the box or via popular libraries (though in non-compiled language, such structures often come with a performance cost). They just don't call them const[ant]s.
Edit: I'm also curious about how you think 'const' is being abused in JS. I'm not an expert in the language--this is a genuine question; not a veiled disagreement.
const x = {};
x.foo = "bar";
The following is perfectly valid code, but breaks almost everything someone would reasonably expect from const.
const foo = {bar: 123};
delete foo.bar;
foo.baz = 456;> You should be using const for everything besides variables that need to get re-assigned.
JS is the one language that very few people bother to learn. They just start writing and see what works. For these people, a const that isn't const isn't a very good idea. Even among the good JS devs I know, most haven't learned this until it actually bit them in production because most books about JS don't mention the problem.
The TDZ (temporal dead zone) is a direct result of adding `const` to the language and it complicates everything (plus has performance implications). A feature that doesn't do what it seems to do while complicating everything else about the language is a textbook example of bad design. There are several people who agree in hindsight (I believe Brendan Eich is among them).
1. JS is in the C/C++/Java lineage syntactically. Ok, that is a deeper design flaw, but Netscape management to keep Sun on board said "Make It Look Like Java".
2. If you want declarations to affect captured expressions, you'll soon want a type system if not immutability controls and defaults. IOW, at least Scheme-like binding rules and set! as special form to use when mutating. Again the ships sailed 23+ years ago, and in truth for "Mocha's" target audience, immutable-by-default would have been harder to use.
"They just start writing and see what works" => a primary design goal. Flawless Victory! :-)
Seriously, the Scheme in the browser baby was killed in the cradle; the recruiting bait used to get me on board was snatched away because of the Sun/Netscape Java deal. All is not lost, as JS grows better special forms (but for backward compatibility must keep old ones). Among these, `const` is least better but still useful.
What's more, those who advocate mass-market immutable-by-default are still working to make it usable in the large (e.g., in Rust). Pedagogy helps, but also has not delivered the goods yet. We are living through the full experiment to refine and confirm that i-b-d is best.
A PHP array works as a sequential or an associative array; or both at the same time
The array syntax can be thought of as a shorthand where you want the indexes inferred from order instead of having to list them out. There are obviously a few useful methods that you use on arrays but almost all of these will work on any object with a length if you .call or .apply them.
If you want to look at a large OpenResty/Lua application from a code perspective you could take a look at Kong[1] - which is the most popular public codebase built on top of NGINX/Lua at the moment.
CloudFlare also uses the same stack but most of their codebase is proprietary.
What really makes Nginx/Lua a good combination is primarily LuaJIT[2] support, a much faster implementation of the Lua VM.
[1] - https://github.com/Kong/kong
[2] - http://luajit.org
For me, day 1 productivity is really high, comparable to Nancy, the framework I was using before.
* http://luajit.org/ext_ffi.html
local ffi = require("ffi")
ffi.cdef[[
int printf(const char *fmt, ...);
]]
ffi.C.printf("Hello %s!", "world")
Using C libraries in regular Lua is fairly easy as well, but LuaJIT is exceptional.
Do you say this because LuaJIT can call shared libraries dynamically? If so, what about ctypes[0]? Is LuaJIT's FFI just easier to use, or does it do something that ctypes can't?
1) The syntax. To specify the types of the FFI functions you you use a DSL that is similar to C declarations. Often you can copy paste function prototypes from ".h" files with very minimal modifications. With ctypes you need to specify the types with Python function calls. See "ffi.cdef": https://luajit.org/ext_ffi.html
2) Performance. If your code is inside a JIT-compiled trace, LuaJIT FFI calls have minimal overhead. They compile down to something very similar to what a C compiler would generate. Ctypes, on the other hand, must "interpret" the FFI calls which adds more runtime overhead (although admittedly this is also true for LuaJIT if your code ends up outside a compiled trace).
The word "configuration" makes repeat performance in that paper, but oddly is entirely missing from this 2018 paper (by the same authors).
Because they seems closely similar to me and Guile is far more clear and effective, at least for my programming skills...
Although I agree it might be difficult to write scripts in C, in the end it might just depend on the core functions that are exposed.
I'm not a fan of C, I prefer python, but I guess I will have less issues when interfacing c code to c++. Python seems quite fat, slow, and too much different than C++.
How so? Do you have an example where Python outperforms Lua or uses significantly fewer resources?
Do you count developer time as a resource?
It depends on your habits. I for one prefer Lua to Python and find it much more pleasurable to code on. There are some things in Python that I like (like the blocks defined by indentation), but overall the language seeems too complex for no reason when coming from lua.
Lua is a small language, it fits in the head with room left over for Python, which is the tool I favor for general-purpose data munging and small OS scripts.
If your case resembles "scripting over a collection of C ABI static or linked libraries" LuaJIT is head and shoulders above the competition. PUC Lua is itself outstanding.
Python is FAT.