Factory function unable to return the local iterator to for loop in lua?

Why can't the factory function fromto return the local function iter as an iterator to the for loop?

function fromto(from,to)
    return iter,to,from-1
end

local function iter(to,from)--parameter:invariant state, control variable
    from = from + 1
    if from <= to then
        return from
    else
        return nil
    end
end

for i in fromto(1,10) do
    print(i)
end

As @YuHao says, your scheme can work. There are a few ways you could rearrange your code. Here's one:

local function fromto(from,to)
    --parameter:invariant state, control variable
    local function iter(to,from)
        from = from + 1
        if from <= to then
            return from
        else
            return nil
        end
    end

    return iter,to,from-1
end


for i in fromto(1,10) do
    print(i)
end

Two things to understand: variable scope and functions are values.

1. Variables are either global or local. Local variables are lexically scoped. They are in scope from the statement following their declaration up to the end of the block. If a name is not the name of a local variable it becomes a global variable reference. On your line 2, iter is a global variable.

2. Functions are not declared, they are values created when a function definition expression is executed. (A function defintion statement is simply an alternate syntax for a function definition expression and assignment to a variable.) Also, functions don't have names. They are simply referenced by one or more variables. So, your function value does exist and get referenced by the iter variable until execution control passes through the lines that contain the function definition. In your code, that's the end of line 11.