Passing argument to lua function after evaluating function in string

as matrix is local function

Lua takes local declarations seriously. If a variable is declared local, it can only be accessed by code which is statically within the local scope of that variable. Strings which you later turn into code are not statically in the local scope and therefore cannot access local variables.

Now, with Lua 5.2+, you can provide load with a second parameter, a table which represents the global environment against which that Lua chunk will be built. If that table contains a matrix value, then the loaded string can access it. For Lua 5.1, you'd have to use setfenv on the function returned to load to accomplish a similar effect. The Lua 5.2+ method would look like this:

local env = {matrix = matrix}
local func = load("return matrix({{2,4,6},{8,10,12},{14,16,20}})", nil, "t", env)
process(func())

Note the following:

• You must create an explicit table which is the global environment. There's nothing you can pass that says "make my locals available"; you have to put every local you'd like to access there. Which is, generally speaking, why you pass these things as parameters or just make them globals.

• You explicitly need the "return " there if you want to get the results of the call to matrix.

• You have to call the function. Functions are values in Lua, so you can freely pass them around. But if you want to pass the results of a function to another function, you have to actually call it.