--[[

In Lua, you can include both functions and values within a table, and by
making each table represent a "thing" ... a.k.a. and object, you can achieve
many of the advantages of object orientation - indeed, you can code using an
OO paradigm. Since assigning a function just copies a reference, you don't
end up with lots of copies of the same code either, and metatables (NOT used
in this example) let you go still further.

In this example, we're loading a file of pet and farm animals into a table
(i.e. a table of tables). Pet and farm animals differ slightly in that
pets have an overall value, but farm animals have a value per kilo. The
test program that uses the data then gives an overall value of all the
animals in our "zoo".

Here are some sample lines of data:

sheep 27 4 f
dog 9 5 p

And now the code ...

]]

-- Define what you can to with a farm animal

farm = {}
function farm.getbreed(current)
        return current.breed
        end
function farm.getweight(current)
        return current.w
        end
function farm.getvalue(current)
        return current.cpk * current.w
        end

-- And define how to create a table for a farm animal

function farm.new(breed,weight,perkilo)
        local now = {}
        now.w = weight
        now.breed = breed
        now.cpk = perkilo
        now.getbreed = farm.getbreed
        now.getweight = farm.getweight
        now.getvalue = farm.getvalue
        return now
        end

-- Define the different things you can do with a pet

pet = {}
function pet.getvalue(current)
        return current.cost
        end

-- And how to create a table for a pet animal
-- n.b. - we have SHARED (inherited) some functions (methods) from farm.

function pet.new(breed,weight,cost)
        local now = {}
        now.w = weight
        now.breed = breed
        now.cost = cost
        now.getbreed = farm.getbreed
        now.getweight = farm.getweight
        now.getvalue = pet.getvalue
        return now
        end

-- As we'll want to load in our animals to lots of applications,
-- let's have that loading code in a separate function which we'll
-- be able to share later

function loadbeasts(source)
        fh,err = io.open(source)
        lno = 0
        zoobase = {}
        while true do
                lyne = fh:read()
                if lyne == nil then break end
                lno = lno + 1
                current = {}
                for f in string.gmatch(lyne,"[^\t\n]+") do
                        current[#current+1] = f
                        end
                if #current == 0 then break end
                if string.match(current[1],"^#") then break end
                if #current ~= 4 then
                        io.write("Error 16 at line "..lno.."\n")
                        break
                        end
                if current[4] == "f" then
                        zoobase[#zoobase+1] = farm.new(current[1],
                                 current[2], current [3])
                elseif current[4] == "p" then
                        zoobase[#zoobase+1] = pet.new(current[1],
                                 current[2], current [3])
                else
                        io.write("Error 17 at line "..lno.."\n")
                        break
                        end
        end
        return zoobase
end

-- Here comes the main program ...

yard = loadbeasts("zoo.txt")

totval_sofar = 0

for _,v in ipairs(yard) do
        a1 = v:getbreed()
        a2 = v:getweight()
        a3 = v:getvalue()
        totval_sofar = totval_sofar + a3
        print (v,a1,a2,a3)
        end
io.write("Total value is "..totval_sofar.."\n")

--[[ ----------------------------------------------

Sample results

[trainee@easterton nats]$ lua anim_o1.lua
table: 0x9983820 turkey 7 14
table: 0x99833f0 sheep 27 108
table: 0x9984018 dog 9 5
table: 0x9984300 hamster 0.1 6
table: 0x9983c78 rabbit 3 12
table: 0x9984c58 dog 28 100
Total value is 245
[trainee@easterton nats]$

]]