The main documentation of the SUM_Integer_Scalar Procedure contains additional explanation of this code listing.
function SUM_Integer_Scalar (I) ! Input variable. type(integer), intent(in) :: I ! Output variable. type(integer) :: SUM_Integer_Scalar !~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ! SUM_Integer_Scalar is equal to I. SUM_Integer_Scalar = I return end function SUM_Integer_Scalar