x = acc(1)                 -- x stores the product with initial value = 1
x(5)                       -- add 5 to x's sum
acc(3)                     -- add 3 to factory's sum
print (x(2.3))  --> 8.3    -- add 2.3 to x's sum then print the result
y = acc()                  -- create new function with factory's sum as initial value
print (y())     --> 4      -- print the accumulated value inside the product y