some lua testing a map function and a linked list, saw this in another lang on this site http://www.braveclojure.com/core-functions-in-depth/

link_list.lua

local LL = {} -- class object

function LL.new(val)
    local self = {}
    self.value = val
    self.next = nil

    function self:first()
        return self.value
    end
    function self:rest()
        return self.next
    end
    function self:cons(val)
        local tmp = LL.new(val)
        tmp.next = self
        return tmp
    end
    function self:repr()
        print(self.value)
        if self.next ~= nil then
            self.next:repr()
        end
    end
    return self
end

function mapp(list, f)
    if list == nil then
        return null
    else
        return list:cons(
            f(list:first()),  -- call the function on the first item in the lits
            mapp(list:rest(), f)) -- call mapp on the rest of the list
    end
end


-- make a linked list node called head
local head = LL.new(10)

-- add a new node onto the front of the node
head = head:cons(20)

-- a function that will print a val if
-- it comes in not nil
function pp(val)
    if val ~= nil then
        io.write(string.format("val: %d\n", val))
    end
end

-- call the mapp function
mapp(head, pp)