The word chunk in Lua means any block of statements that are compiled as a unit. The most obvious example is a Lua file. I'll create a new file to demonstrate.
Chunks are always treated as the body of a function, which has two consequences. First, local variables are not visible outside the chunk. Second, you can return values, which stops the execution of the chunk.
-- In the file example.lua:
local x = 1
y = 2
return 'w00t'
In the interpreter, I'll use the built-in dofile function to
execute the script I just wrote.
The global x is left undefined since it was a local in the file:
> = x
nil
The global y is defined:
> = y
2
and the return value r has been received from the file:
> = r
w00t
Any code executed in the interpreter is compiled as a chunk.
This means that variables declared as local aren't visible in the
next chunk, like this:
> local x = 64
> = x
nil
They are visible within the same chunk, though:
> local x = 64; print(x)
64
The semicolon, by the way, is an optional line separator in Lua.
I can also return values from an interpreter line, like this:
> return 1, 2, 3
1 2 3
The default action of the interpreter is to print out the return values.
In Lua 5.2 and later, there's a nice built-in function called load
which accepts a string, compiles it as a Lua chunk, and returns a
function you can call to execute that chunk.
In Lua 5.1, which I'm using here, you want to call loadstring
to perform the same action.
Here is an example:
> f = loadstring('print("hi")')
Notice that my code hasn't run yet.
It's only been compiled so far. I can call f to run the chunk:
> f()
hi
Lua has two types of comments - single-line and multi-line. To illustrate that, I'll create a new Lua file. Here is a regular Lua statement:
-- In the file comments.lua:
print('string 1')
If at any point, Lua sees two hyphens, then the rest of that line is a comment.
-- Adding to the previous line in comments.lua:
print('string 1') -- print('string 2')
To start a multiline comment, you need to use two hyphens followed by two open square brackets. To show that this is in fact a multiline comment, I'm going to put in multiple lines:
-- Appending in the file comments.lua:
--[[
print('string 3')
print('string 4')
--]]
We'll see that they're not executed.
To show that this is the end [of the comment block], and that they're executed again, I'll create another statement:
-- Appending in the file comments.lua:
print('string 5')
When I run this, we should only see strings 1 and 5 printed out because the rest are commented.
> dofile('comments.lua')
string 1
string 5
There you go!
Next