wtf.lua

local function append(x, a, ...)
	if not a then return x end
	return a, append(x, ...)
end

local function seek(n, x, ...)
	if n < 0 then error() end
	if n == 0 then return x end
	return seek(n - 1, ...)
end

local cat
do
	local function catcore(n, b, ...)
		if not seek(n, b()) then
			return ...
		end
		return catcore(n + 1, b, append(seek(n, b()), ...))
	end
	cat = function(a, b)
		return catcore(0, b, a())
	end
end

local function reduce(f)
	local function r(a, b, ...)
		if not b then return a end
		return r(f(a, b, ...), ...)
	end
	return r
end

local conscat = reduce(function(a, b)
		return function() return cat(a, b) end
	end)

local function catall(...)
	return conscat(...)()
end

local function length(...)
	return reduce(function(a) return a + 1 end)(0, ...)
end

local function map(f, a, ...)
	if not a then return end
	return f(a), map(f, ...)
end

local function decons(a, b, ...)
	if not b then return function() return a end end
	return conscat(map(decons, a, b, ...))
end

print(map(function(x) return x * 2 end,
	catall(
		decons(1, 2, 3),
		decons(4, 5, 6),
		decons(7, 8, 9))
))