Pure procedures are a feature of Fortran 95. A pure procedure has no side effects. Causes their value to change. Creates a pointer to that variable. It can be called from a pure procedure.
Pure procedures can only call other pure procedures.
It can be passed as an actual argument to a pure procedure. If a procedure is used in any of these contexts, its interface must be explicit and it must be declared pure in that interface. On elemental procedures, see Section 8.5.1.3 . On pure procedures in interface blocks, see Section 8.9.2 . On how to use pure procedures, see the Compaq Fortran User Manual for Tru64 UNIX and Linux Alpha Systems .