How does the function returned from pairs work?

In for in loop we see this pattern:

local T= {}   
T.apple = 10;   
T.banana = 5;   
T.orange = 4;   
   
for K,V in pairs(T) do   
   
end   

How does this actually work under the hood?

The pairs function returns a function which is called an iterator function.

We can call this function to iterate through the keys in the table:

function main(Data)   
   local T  = {}   
   T.apple  = 10;   
   T.banana = 5;   
   T.orange = 4;   
   
   local Iterator = pairs(T)   
   trace(Iterator)   
   local K, V   
   
   K,V = Iterator(T, nil)   
   trace(K,V)   
   K,V = Iterator(T, K)   
   trace(K,V)   
   K,V = Iterator(T, K)   
   trace(K,V)   
   K,V = Iterator(T, K)   
   trace(K,V)   
   
   repeat   
      K,V = Iterator(T, K)   
      trace(K,V)   
   until K == nil   
end