Lua on the iPhone?

Question

I am trying to use Lua on the iPhone. On Mac OS X, in a normal (non-iOS) Cocoa application, I used the following code:

lua_State* l;
l = lua_open();
luaL_openlibs(l);
luaL_loadstring(l, "print(\"Hi from Lua\");");
lua_pcall(l, 0, 0, 0);

I downloaded Lua 5.1.4 from lua.org/ftp and compiled it for Mac OS X. In the Xcode project, I used "Add Existing Framework" to add liblua.a and I used "Add Existing Files" to add the include directory.

This works as expected, and prints the string: "Hi from Lua". When I try the same thing in an iOS project, it gives the errors:

"_luaL_newstate", referenced from:
_main in main.o
more of the same thing...
symbol(s) not found
collect2: ld returned 1 exit status

It seems that the .a file is not linked into the iPhone app. Does anybody know how to make this work?

(By the way, I don't really care that Apple might not accept my app if it has Lua in it.)

Answer 1

You'll need to compile the Lua .a for ARM, not Intel. If the Lua library uses autoconf, you can use my favorite iphone/autoconf builder: build_for_iphoneos. If it's not autoconf, then you can use that script to get an idea of how to attack it. Sometimes you can just build a Static Library Xcode project, dump all the files into it and hit build. If the build is simple enough, it'll do most of the work for you.

I know it doesn't matter for your use, but Lua-based tools are generally shippable on the app store. You just can't download arbitrary code at run time and interpret it.

Answer 2

You might want to check out iPhone Wax. It is a lua/iPhone bridge that lets you write native iPhone apps in pure lua! Here is a pretty good tutorial about it.

Answer 3

If you want to write Lua code for iOS, then check out MOAI immediately: http://getmoai.com/

Its an absolutely enjoyable framework for developing games on iOS and Android, as well as Windows and OSX. Not only that, but it provides a pretty good idea of how to properly implement a Lua-VM based hosting environment for scripting in a cross-platform manner: from MOAI, you can learn a lot about this. I've done 4 titles with MOAI so far, and won't be stopping any time soon .. MOAI absolutely kicks ass!

Also check out LOAD81, which is a similar effort albeit with SDL as the target environment: http://github.com/antirez/load81

(I've contributed a little to the LOAD81 project, specifically giving it features of interest/value to the OpenPandora community. MOAI is more commercial, LOAD81 more hobbyist..)

For those trying to learn Lua and the different methods of integrating the Lua VM in a project for multiple platform targets, both MOAI and LOAD81 can provide a lot of great background and clues about the right way to proceed.