-- tostring replacement that assigns ids
local ts, id, nid, types = tostring, {}, 0, { table = 'tbl', thread = 'thr', userdata = 'uda', ['function'] = 'func' }
tostring = function(x)
	if not x or not types[type(x)] then return ts(x) end
	if not id[x] then nid = nid + 1; id[x] = types[type(x)] .. '.' .. nid end
	return id[x]
end


function a()
	return pcall(function() end)
end

function b()
	return pcall(function() print 'b' end)
end

function c()
	return pcall(function() return 'c' end)
end

print(pcall(a))
print(pcall(b))
print(pcall(c))

local function sum(...)
	local s = 0
	for i, v in ipairs({ ... }) do
		s = s + v
	end
	return s
end

local function f1(n, a, b, c)
	local a = a or 0
	local b = b or 0
	local c = c or 0
	if n <= 0 then
		return a, a + b, a + b + c
	end
	return f1(n - 1, a, a + b, a + b + c)
end

local function f2(n, ...)
	if n <= 0 then
		print(" --f2, n<=0, returning sum(...)", ...)
		return sum(...)
	end
	print(" --f2, n>0, returning f2(n-1,n,...)", n - 1, n, ...)
	return f2(n - 1, n, ...)
end

local function f3(n, ...)
	if n <= 0 then
		return sum(...)
	end
	print("    f3,n-1,n,...", f3, n - 1, n, ...)
	return pcall(f3, n - 1, n, ...)
end

local function all(f)
	for n = 0, 3 do
		t = {}
		for m = 1, 5 do
			print("--f, n, unpack(t)", f, n, unpack(t))
			print(pcall(f, n, unpack(t)))
			t[m] = m
		end
	end
end

all(f1)
all(f2)
all(f3)


local function f(x)
	-- tailcall to a builtin
	return math.abs(x)
end

local function factorial(i)
	local function helper(product, n)
		if n <= 0 then
			return product
		else
			-- tail call to a nested Lua function
			return helper(n * product, n - 1)
		end
	end

	return helper(1, i)
end

local result1 = factorial(5)
print(result1)
print(factorial(5))

local result2 = f(-1234)
print(result2)

local function fib_bad(n)
	local function helper(i, a, b)
		if i >= n then
			return a
		else
			-- not recognized by luac as a tailcall!
			local result = helper(i + 1, b, a + b)
			return result
		end
	end

	return helper(1, 1, 1)
end

local function fib_good(n)
	local function helper(i, a, b)
		if i >= n then
			return a
		else
			-- must be a tail call!
			return helper(i + 1, b, a + b)
		end
	end

	return helper(1, 1, 1)
end

local aliases = {
	['1.#INF'] = 'inf',
	['-1.#INF'] = '-inf',
	['1.#IND'] = 'nan',
	['-1.#IND'] = 'nan',
}

local p = function(s, e)
	print(s, e and aliases[tostring(e)] or e)
end
p(pcall(fib_bad, 30))
--p((pcall(fib_bad, 25000)))
p(pcall(fib_good, 30))
p(pcall(fib_good, 25000))

local function fib_all(n, i, a, b)
	i = i or 1
	a = a or 1
	b = b or 1
	if i >= n then
		return
	else
		return a, fib_all(n, i + 1, b, a + b)
	end
end

print(fib_all(10))
