Lua references and guides

Codea version 1.5 uses version 5.1 of Lua (as demonstrated by the result of the statement print(_VERSION)). The following sites have information you may find useful about the Lua language and programming in it:

• Lua version 5.1 reference manual: The version used by Codea.
• Programming in Lua (1st Ed): Aimed at version 5.0 of Lua, but remains largely relevant to version 5.1.
• lua-users.org: An internet site for and by users of the programming language Lua.

Frequently asked questions

The following Lua-specific matters frequently give rise to questions or requests for help on the Codea Forum.

'Full stop' syntax and the 'colon' syntax

The 'full stop' syntax myVariable.Name is a shorthand for the syntax myVariable["Name"]. It is used to index Lua tables and certain Codea userdata types.

The 'colon' syntax in function calls myVariable:Name(...) is a shorthand for the syntax myVariable.Name(myVariable, ...). It is used to implement features in Lua that are like object-oriented programming (OOP).

The 'colon' syntax in function definitions function myVariable:Name(...) is a shorthand for the syntax function myVariable.Name(self, ...). Again, it is used to implement features in Lua that are like OOP. It is used extensively together with the class() function provided by the Codea API.

For example:

c = color(255, 0, 0, 255) -- Opaque red
myMesh = mesh()
myMesh:setColors(c) -- Correct: Equivalent to myMesh.setColors(myMesh, c)
myMesh.setColors(c) -- Wrong: Will result in an error that the first argument is bad and not a mesh

Short-cut evaluation of operators and and or

Like many other programming languages, Lua uses short-cut evaluation for the logical operators and and or.

and returns its first argument if this value is false or nil, and does not evaluate the second operand in those circumstances.

or returns its first argument if this value is different from false and nil, and does not evaluate the second operand in those circumstances.

For example:

function message()
    print("Message has been called!")
    return true
end

function setup()
    print(true or message()) -- Output: true
    print(message() or true) -- Output: Message has been called!
end