That's three ways to run Lua code. Lua also runs from embedded apps.
Let's talk about types.
These are all 8 types in Lua. I'll mainly talk about these 6 highlighted types in this video.
true and false are the boolean values.
> a = true
> b = false
The built-in type function returns a string indicating the type of the input.
> = type(a)
boolean
There's a single number type. You can type numbers in standard decimal notation, scientific notation,
> print(4.22e1)
42.2
or in hex.
> print(0x10)
16
In Lua 5.2 and earlier, numbers are represented internally as 64-bit doubles by default. Lua 5.3 still has a single number type, but it can internally use either an integer or a double representation.
The built-in tonumber function converts numbers and strings to numbers.
> = tonumber('2.7')
2.7
Lua strings are immutable. You can use single- or double-quotes to specify them. It doesn't make any semantic difference which type of quotes you use.
> s1 = 'hi'
> s2 = "hi"
> = (s1 == s2)
true
These literals can have the usual escaped characters like newlines and tabs.
> print('hi \n there \t \\')
hi
there \
Lua strings internally are arbitrary-length byte sequences; zero bytes are allowed. Type a backslash followed by up to three decimal digits to specify arbitrary bytes.
> = '\65\66\67\0'
ABC
Multiline strings can start with two open square brackets. They don't allow escaped characters within this type of string.
> print([[
one
two
three]])
one
two
three
The built-in tostring function returns a reasonable
string representation of any value.
> = tostring(true)
true
Tables are key-value maps, and Lua's only container type. I'll cover tables later in the video.
The nil value conceptually means no value.
Undefined variables evaluate to nil; it's not an error.
> = abc
nil
Setting values to nil
undefines them and allows them to be
garbage collected.
> s1 = nil
You can also explicitly call collectgarbage(), but usually you
don't have to because the garbage collector is running automatically.
> collectgarbage()
Functions can be assigned to variables and passed into and out of other functions. I'll talk more about functions later in the video.
> fn = function (x) return x*x end
> = fn(3)
9
Userdata and threads are slightly advanced types that
I won't cover in detail now.
A userdata object is basically a black-box type used by libraries
to wrap C-level structs like a FILE * from C's stdio library.
> f = io.open('file', 'w')
> = type(f)
userdata
A thread is a coroutine instance.
Assignments are global by default.
Use local to make them local.
> local a = 7