@Sebastiano Good morning, I hope all is ok. nullschool earth (no idea why it's called so) is such a nice web. You can have several overlays, also rain: earth.nullschool.net/#current/wind/surface/level/… ;-)
@Rmano Good morning to you dearest. The current situation is bad but not serious. There is flooding and high winds. There is now a very strong flood coming. I thank you very much for your interest. I had never seen so much rain and wind in my life. I feel like I am in a tropical zone. I hope it doesn't do any damage.
I am by far a person that can give you an authorative answer. As I have written in a comment to David, there is no way to use TeX as a (shared) library. But you can use LuaTeX to load modules and execute LuaTeX's functions.
Say you want to call texio.write_nl("Hello world!"). You have to write a...
I don't understand why it's necessary to have
lua_remove(L, -2);
Of course I only have a very sketchy idea of what is happening here, but why remove this before the function call has happened?
I tried it without, and it seems to work.
I'm also not clear why it works without. Doesn't the function need to be pushed on the stack before it is called?
lua_getglobal(L, "texio"); /* table to index */ lua_getfield(L, -1, "write_nl"); /* function to be called */ lua_remove(L, -2); /* remove table texio from stack */ lua_pushstring(L, "Hello, world!"); /* push first argument to stack */ lua_call(L, 1, 0); */ call function with 1 argument and without result */
This is the breakdown of the function you did not understand. So how does `lua_call` know which function to call? Because given the stack pointer it calculates where to go for a function with 1 argument and without result and then performs the call.
@FaheemMitha It doesn't need to do that, but since texio is no longer needed it's good programming technique to remove it instead of leaving it on the stack.
@FaheemMitha Yes, it offsets from the top of the stack (stacks are structures where your only way to retrieve data is from the top so you would have to jump through hoops to actually implement everything else and it wouldn't be particularly stack-like).
@FaheemMitha Ever heard of stack overflows? Well, if you leave stuff on the stack and do not clean up you might fill the available space and at some point … you guess it. No longer needed is everything that has been consumed, e.g. a function and its arguments after lua_call (which actually pops the stack accordingly).
@TeXnician My question is why the "function" or "function value", if you prefer, it popped before the function call for that "function" is actually made.
Imagine that the Lua interpreter needed to get texio to look where to find write_nl. But as soon as it figured out where it would find write_nl (the address of the function the table is pointing to) it doesn't need texio anymore. Lua tables are basically many pointers.
@TeXnician So when it pushes write_nl, then it has obtained the function? But I thought that in a stack, when the earlier ones were popped, the later ones were also popped? So if texio is popped, isn't write_nl forced to be popped too?
@FaheemMitha No, in Lua certain operations can change elements of the stack directly, even if they are not on the top. If a function is documented to remove one element, then it only removes this one element.
@FaheemMitha Well, iirc remove is actually doing the following: pop everything into a temporary second stack until the index to remove is found, then pop the second stack and push everything back to the regular stack. So indeed it is popped but also pushed again. (This is theory and nearly surely not how the implementation will do it.)
So you can express all of this in stack operations but it would be expensive to implement it that way ;)
@FaheemMitha I would say, especially then it is not. Because it just depends which abstract data type your stack is trying to implement. And at some of them it is just a bad choice but stacks are a very simple model for the mind ;)
@MarcelKrüger @TeXnician So if a Lua C function says it removes or pops a value from the stack, one should assume that only that one has been removed or popped? Not the ones after it?
@FaheemMitha If it removes a value, you should assume that it only removes that value. It will normally not call it pops since pop specifically refers to removing the top element.
E.g. lua_pop(L, 2) would remove both elements on the top. (what you thought lua_remove(L, -2) did)
@FaheemMitha But generally: Read the official documentation. E.g. for lua_remove it explicitly says what happens with higher elements on the stack, so it's pretty clear that they aren't removed.
@samcarter -- Darn, it's supposed to rain here, with patchy fog. At least it won't be like the storm we had a few days ago. Power outages all over the place, and some of our neighbors didn't get turned back on until today. (We were spared, thankfully.)
@mickep @samcarter @UlrikeFischer Thanks for all your suggestions. Since I produce Beamer slides with markdown (because the markup:content ratio is much too high otherwise) I've been trying to stick to things that can be done that way, but it doesn't really look like it's possible, so I'll just embed raw LaTeX into the markdown, in which case I can use a regular linguistic example package.
