How to iterate over pairs of elements in table in lua

Question

How to iterate over pairs of table elements in lua? I would like to achieve a side-effect free way of circular and non-circular iterating ver pairs.

I have table like this:
t = {1,2,3,4}

Desired output of non-circular iteration:
(1,2)
(2,3)
(3,4)

Desired output of circular iteration:
(1,2)
(2,3)
(3,4)
(4,1)

Answer 1

Here's the circular case

for i = 1, #t do 
  local a,b
  a = t[i]
  if i == #t then b = t[1] else b = t[i+1] end 
  print(a,b) 
end

Non circular:

for i = 1, #t-1 do 
  print(t[i],t[i+1]) 
end

For fancier output use print(string.format("(%d,%d)",x,y)