Как в LUA реализовать струтуру данных - аналог perl-ового хеш хешей?

> a = { b = { c = "yes"}}
> = a.b.c
yes

tb = { foo = { bar = "baz" } }
print(tb["foo"]["bar"])

tb.foo = nil

b = 'sdf'
c = 'zxc'
a = { b = { c = "yes"}}

b = 'sdddd'
c = 'zdddd'
a = { b = { c = "no"}}

b = 'sdddd'
c = 'zddde'
a = { b = { c = "no"}}

b = 'sddff'
c = 'zddff'
a = { b = { c = "yes"}}

b = 'sddff'
c = 'zeeff'
a = { b = { c = "yes"}}

b = 'sddff'
c = 'zdeff'
a = { b = { c = "yes"}}

Как распечатать элементы хэша первого уровня, второго чтобы была видно вложенность?

b = 'sdf'
c = 'zxc'
a = { [b] = { [c] = "yes"}}

a = { [b] = { [c] = "yes"}} 

a = { b = { c = "yes"}}

local c
for k,v in ipairs(a) do
    for m in ipairs(a.k) do
        print (k .. " => " .. v)
        c = c + 1
    end
    print ("Всего элементов для: ", k ," ", c)
end

a = { [b] = { [c] = "yes"}}

> b = 'sdf'
> c = 'zxc'
> a = { [b] = { [c] = "yes"}}
> = a.sdf.zxc
yes
> = a["sdf"]["zxc"]
yes

function printtbl(tbl)
 for k,v in pairs(tbl) do
   if type(tbl) == "table" then 
     printtbl(tbl)
  else
    print(k,v)
  end
end

printtbl(tbl)

local c = 0
for k,v in pairs(a) do
    for m in pairs(a[k]) do
        print (k, " => ", v[m])
        c = c + 1
    end
    print ("Всего элементов для: ", k ," ", c)
end

/usr/local/bin/luajit-2.0.0: ./hoh2.lua:44: stack overflow
stack traceback:
        ./hoh2.lua:44: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ...
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:46: in function 'printtbl'
        ./hoh2.lua:53: in main chunk
        [C]: at 0x0804b4f0

function printtbl(tbl)
  local write = io.write
  for k,v in pairs(tbl) do
    if type(v) == "table" then
      write("{ ")
      printtbl(v)
      write("} ")
    else
      write(k, "=>", v, " ")
    end
  end
end

printtbl(a) ; print()

b = 's1'
c = 'zxc'
a = { [b] = { [c] = "yes"}}

b = 's2'
c = 'zdddd'
a = { [b] = { [c] = "no"}}

b = 's2'
c = 'zddde'

a = { [b] = { [c] = "no"}}

b = 's3'
c = 'z1'
a = { [b] = { [c] = "yes"}}

b = 's3'
c = 'z2'
a = { [b] = { [c] = "no"}}

b = 's3'
c = 'z3'
a = { [b] = { [c] = "yes"}}

print (a["s3"]["z3"])
print (a["s3"]["z2"])
print (a["s3"]["z1"])

function printtbl(tbl)
    local write = io.write
    for k,v in pairs(tbl) do
        if type(v) == "table" then
            write(" {")
            printtbl(v)
             write("} ")
        else
            write(k, "=>", v, " ")
        end
    end
end

printtbl(a) ; print()

# ./hoh4.lua
yes
nil
nil
 {z3=>yes }

Lua { b = 1 }

Perl { b => 1 }

Lua { [b] = 1 }

Perl { $b => 1 }

function printtbl(tbl)
    local write = io.write
    for k,v in pairs(tbl) do
        if type(v) == "table" then
            write(k, " => {")
            printtbl(v)
            write("} ")
        else
            write(k, " => ", v, " ")
        end
    end
end

Также по аналогии:

Lua:  x = "some key"
Perl: $x = "some key"

Lua:  t.x     равнозначно t["x"]
Perl: $t->{x} равнозначно $t->{"x"}

Lua:  t[x]
Perl: $t->{$x}

cars = {
    {
        name = "Toyota",
        year = 2005,
    },
    {
        ["name"] = "Nissan",
        ["year"] = 2001,
        info = {
            nOwners = 2,
        },
    },
}

function showkv(k, v)
    if type(v) == "table" then
        v = string.format("{\n%s,\n}", show(v))
    elseif type(v) == "number" then
        v = string.format("%d", v)
    else
        v = string.format("%q", v)
    end
    if type(k) == "number" and math.floor(k) == k then
        k = string.format("%d", k)
    else
        k = string.format("%q", k)
    end
    return string.format("[%s] => %s", k, v)
end

function show(t)
    local lines = { }
    for k,v in pairs(t) do
        lines[#lines+1] = showkv(k, v)
    end
    return table.concat(lines, ",\n")
end

print(show(cars))
print(cars[1].name)
print(cars[2].name, cars[2].info.nOwners)
print(cars[2]["name"], cars[2]["info"]["nOwners"])

a["foo"] = {["bar"] = "baz"}

a = {}
a["foo"] = {["bar"] = "baz"}

b = 's2'
c = 'z1'
d = 'z2'
a[b] = { [c] = "s2z1" , [d] = "s2z2" }

результат s2 => {z1 => s2z1 z2 => s2z2} (последний элемент)

b = 's2'
c = 'z1'
a[b] = { [c] = "s2z1" }

b = 's2'
c = 'z2'
a[b] = { [c] = "s2z2"}

результат s2 => {z2 => s2z2}

результат s2 => {z1 => s2z1}
результат s2 => {z1 => s2z1 z2 => s2z2}
результат s2 => {z1 => s2z1 z2 => s2z2 z3 => s2z3 }
результат s2 => {z1 => s2z1 z2 => s2z2 z3 => s2z3 z4 => s2z4 }
и т.д.

a = { }
a[b] = { } -- создаем подтаблицу
c = ...
a[b][c] = x -- пишем в нее
c = ...
a[b][c] = y -- пишем в нее

-- А ты затираешь каждый раз a[b] новой таблицей.

t = { }
function addrelation(ipa, ipb)
  t[ipa] = t[ipa] or { }
  t[ipa][ipb] = true
end

...

addrelation(x, y)
addrelation(x, z)

if t[x][y] then
  -- x relates with y
end

-- remove relations for ipa
t[ipa] = nil


for ipa,subt in pairs(t) do
  for ipb in pairs(subt) do
    print(ipa, "relates to", ipb)
  end
end