Functions

Last time I talked about scope and Lua blocks of code which are called "chunks". A function, in Lua, is a named chunk of codde using the syntax:

function name([parameters])
— code here
end

And here is an example that prints "Hello Lua" and takes no parameters:

function HelloWorld()
h = "Hello"
w = "Lua"
print(h .. " " .. w)
end

Calling a function is similar to other languages. You use the name of the function followed by any arguments in parentheses.

HelloWorld()

Here is an example that multiplies two numbers:

function MultiplyTwoNumbers(x,y)
local result = x * y
print(x .. "*" .. y .. "=" ..result)
end

MultiplyTwoNumbers(3,217)

This is what it looks like when you run it:



The number of arguments and parameters doesn't have to match in Lua. Extra arguments are ignored. Too few arguments are passed in with a nil value. Of course, if you use the missing argument in a way that doesn't make sense, you'll get an error as in the second call to MultiplyTwoNumbers here.



As in other languages, Lua functions can return values using a return statement.

function MultiplyTwoNumbers(x,y)
local result = x * y
local answer = x .. "*" .. y .. "=" .. result
return answer
end

print(MultiplyTwoNumbers(3,217))

Lua can also return more than a single value from within a function. Unlike other languages, this is not treated as a tuple.

function AreaAndCircumference(radius)
local area = 3.14 * radius * radius
local circumference = 2 * 3.14 * radius
return area, circumference
end

a, c = AreaAndCircumference(12.3)
print("Area:" .. a)
print("Circumference:" .. c)



You can ignore trailing return values. So in this example I could have said:

a = AreaAndCircumference(12.3)

I haven't looked to see if there is a way to ignore leading or embedded return values.

Operators

Most of the Lua operators are standard (or familiar).

• +
• -
• *
• /
• % (modulo)
• ^ (exponent)
• ==
• ~= (not equal)
• <
• >
• <=
• >=
• and
• or
• not

I've mentioned one unique operator, concatenation.

• ..

I'll look at control structures (conditionals and loops next time.

Tags: Lua, function, parameter, calling, declaring, chunks, arguments, operators