The previous section lays out the rules and considerations for execution models defined for HPF extrinsics. The HPF extrinsic interface is also used to tell the compiler what the language conventions of a called subprogram are. Four language bindings are defined here: HPF, Fortran, F77, and C. A given implementation may support additional interfaces or allow a user to construct custom interfaces. Taken together, these sections define the special extrinsics HPF_LOCAL and HPF_SERIAL.
The key feature of the language interface is an extended set of attributes for dummy arguments in explicit extrinsic interfaces, which can give the programmer control over aspects of argument passing between procedures of different extrinsic types. This mechanism is used extensively in the interfaces to C and Fortran 77, but it is defined in this more general context because it can also apply to other language interfaces.