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require 'classlib'

class.Tuple()

function Tuple:__init(...) -- construct with initial elements

self.elem = {...}

self.n = #self.elem

end

function Tuple:__tostring() -- string representation

local function ascii(e)

return type(e) == 'string' and string.format('%q', e) or tostring(e)

end

local s = ''

for i, v in ipairs(self.elem) do

s = #s == 0 and ascii(v) or s .. ', ' .. ascii(v)

end

return '(' .. s .. ')'

end

local function checkrange(i, max)

assert(i >= 1 and i <= max,

'Index must be >= 1 and <= ' .. max)

end

local function checkindex(i, max)

assert(type(i) == 'number', 'Index must be a number')

checkrange(i, max)

end

function Tuple:push(i, v) -- push an element anywhere

if v == nil then

v = i

i = self.n + 1 -- by default push at the end

end

if v == nil then return end -- pushing nil has no effect

checkindex(i, self.n + 1) -- allow appending

table.insert(self.elem, i, v) -- insert it

self.n = self.n + 1 -- count it

end

function Tuple:pop(i) -- pop an element anywhere

if i == nil then

i = self.n -- by default pop at the end

if i == 0 then return nil end

end

local e = self[i]

self[i] = nil -- remove it

return e -- return it

end

function Tuple:clear() -- empty tuple

self.elem = {}

self.n = 0

end

function Tuple:size() -- tuple size

return self.n

end

function Tuple:__get(i) -- read an element

if type(i) ~= 'number' then return nil end

checkrange(i, self.n + 1) -- allow reading one past the end

return self.elem[i] -- read it

end

function Tuple:__set(i, v) -- assign an element

if type(i) ~= 'number' then return false end

checkrange(i, self.n + 1) -- allow assigning one past the end

if v == nil then

if i <= self.n then -- if removing, count it

table.remove(self.elem, i)

self.n = self.n - 1

end

return true

end

if i == self.n + 1 then -- if appending, count it

self.n = i

end

self.elem[i] = v -- assign it

return true

end