Why Lua? • Hacker News Board

Re: Why Lua?

#31

Post by sshumaker » Tue, Jan 31, 2012, 11:47 PM UTC

gregholmberg wrote: post #13

meric wrote: post #8

In lua, the metatable is the killer feature that python doesn't have.

When my main language was C, I used to feel that dynamically mutating or self-modifying data structures were somewhere between black magic and heresy. I have found that being able to place arbitrary constraints on the way my programs store things in (seemingly simple) data structures has been very, very powerful.

metatables don't involve dynamically mutating / self-modifying data structures. They're more equivalent to javascript's prototype, except slightly more general-purpose. You can easily use them to build an OO system, among other things.

Re: Why Lua?

#32

Post by sshumaker » Tue, Jan 31, 2012, 11:50 PM UTC

haberman wrote: post #14

The more I learn about Lua's design and implementation, the more impressed I am. It's very rare to see software that does so much with so little code. The design is extremely clean and the code is extremely fast. The C API is easy to use and gives good performance, and yet encapsulates enough of the VM's implementation that C modules are source and binary compatible with both Lua and LuaJIT, two very different implem…

Lua has great C integration, but LuaJIT's is even better. You can natively interface with C code without a recompile, just by defining the C function prototype in Lua, and using it like you would any normal lua function. Better still, LuaJIT can frequently inline the calls to C code, so there's no cross-language marshaling penalty.

Check out http://luajit.org/ext_ffi_tutorial.html

Re: Why Lua?

#33

Post by sshumaker » Tue, Jan 31, 2012, 11:52 PM UTC

peregrine wrote: post #29

justincormack wrote: post #18

Earlier quoted context omitted.

There are several server side Lua options with coroutines.

Could you name a few, alls I see are kepler based ones..

The previously mentioned luvit (http://luvit.io) has them (they call them Fibers).

Re: Why Lua?

#34

Post by timmaxw » Tue, Jan 31, 2012, 11:52 PM UTC

I've used Lua for a couple of personal projects. My main objection to it is that accessing an undefined variable or member returns nil rather than throwing an exception. If you make a typo, you don't find out until you try to call or perform arithmetic on your nil value. Since inserting nil into a table just deletes that key of the table, the use site might be several steps away from the typo.

Other than that, I agree with the other posters here. It's an impressively lightweight and elegant language. It's especially good for embedding: its C integration is next to none, it's easy to sandbox if you want to run untrusted code, and the interpreter doesn't use any global variables.

Re: Why Lua?

#35

Post by 6ren » Tue, Jan 31, 2012, 11:56 PM UTC

chubot wrote: post #6

Why isn't Lua more widely used? One reason is a consequence of it being an embedded language. Lua has had 5 major versions which are very incompatible with each other. You're just supposed to stick with the previous version until you upgrade your code. I read all the Lua papers, and they are quite fond of "getting it right" (which is refreshing). They will break things to get it right, whereas other languages stick w…

Is ability to break compatibility due to being embedded?

I recall that MS ships with each game the exact version of DirectX it need, so they are free to improve it without being hamstrung by back-compatibility.

Re: Why Lua?

#36

Post by sshumaker » Tue, Jan 31, 2012, 11:57 PM UTC

hythloday wrote: post #22

meric wrote: post #8

In lua, the metatable is the killer feature that python doesn't have.

Could you explain what you can accomplish with Lua metatables that you can't do with python __eg__ methods? I've only seen them used as a way to implement operator overloading.

__index and __newindex are the key ones - effectively equivalent to method_missing in Ruby. __index gets called if you try to read a non-existent key, and __newindex gets called if you try to write to a non-existing key. You can use these methods to implement inheritance, proxies, getters/setters, all sorts of stuff.

Re: Why Lua?

#37

Post by jballanc » Wed, Feb 01, 2012, 12:03 AM UTC

groovy2shoes wrote: post #4

Good article, but one nitpick: not everything in Lua is a table. Tables are a versatile data structure that can be used as arrays, dictionaries, objects, etc. However, Lua provides many types besides tables: numbers, booleans, closures (functions), strings (which are interned), coroutines, and something called userdata (which are typically pointers to something implemented in C). Another cool thing about Lua, which w…

To nitpick your nitpick: in Lua tables are the only composite data structure. Everything you listed is either atomic or opaque (you can hide composite datatypes in userdata, but you can't introspect the values).

If you think about it, this is very similar to C where the only composite datatype is a struct (arrays are just sugar on pointer arithmetic). In fact, I think if you wanted to make a scriptable dialect of C, you'd create Lua.

Of course, by being simple, add in dynamic typing and first-class functions, and Lua does feel a bit like Scheme's kid brother. Or, rather, Lua (in my mind) reveals how C and Scheme aren't so far apart after all!

Re: Why Lua?

#38

Post by sshumaker » Wed, Feb 01, 2012, 12:04 AM UTC

marshray wrote: post #19

To echo chubot: Why isn't Lua more widely used? * It lacks an easy-to-use symbolic debugger. * It lacks a first-rate IDE. * It lacks a standard way for people coming from OO/Java to define objects and interfaces. * It lacks a GUI toolkit. * It has a great set of manuals. It lacks an O'Reilly book with a woodcut animal on the cover. * Arrays indexes start at 1. Except for the last item, these are all relatively small…

Lua's original focus as an embedded language has been a huge handicap here. There's almost no standardization, because each developer builds their own set of libraries based on their needs. It's sort of what server-side javascript looked like before node.js.

Lua is in dire need of an opinionated killer platform. Unfortunately, unfamiliarity with the language (vis-a-vis javascript) means that the road to mass adoption is a tougher one.

Re: Why Lua?

#39

Post by silentbicycle » Wed, Feb 01, 2012, 12:09 AM UTC

chubot wrote: post #6

Why isn't Lua more widely used? One reason is a consequence of it being an embedded language. Lua has had 5 major versions which are very incompatible with each other. You're just supposed to stick with the previous version until you upgrade your code. I read all the Lua papers, and they are quite fond of "getting it right" (which is refreshing). They will break things to get it right, whereas other languages stick w…

It's easier to break reverse compatibility when your whole language is a 200k DLL and MIT Licensed. If people need to stick with version 4.0, it's realistic to maintain an in-house fork.

Re: Why Lua?

#40

Post by sshumaker » Wed, Feb 01, 2012, 12:10 AM UTC

munchor wrote: post #16

The worst problem with Lua is that arrays start at 1. That is way too bad for me to use it. I only use it to configure Awesome WM, but it sucks for everything else IMO because of "tables" starting at 1.

It's annoying, especially if you switch between languages frequently.

My first task in Lua was to build a solid collections library (modeled after Ruby's), so this issue comes up far more infrequently for me now. (e.g. I use :first(), :last(), :push(), etc instead of [1], [#length], [#length + 1])