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