IRPF90 is a Fortran code generator. Schematically, the programmer only writes computation kernels, and IRPF90 generates the glue code linking all these kernels together to produce the expected result, handling all relationships between variables. To illustrate in a few words how IRPF90 works, let us consider the simple example which consists of calculating the total energy of a molecular system as the sum of the nuclear repulsion and the electronic energy