GKS Inquiry Functions within PROLOG

GKS, the international standard for 20 graphics software, provides a set of functionalities which are specified in a language independent manner. However, for GKS to be used, a binding must be defined for some host programming language. To date a FORTRAN binding [1] has been accepted, and proposals for bindings in Pascal [8] and Ada are under consideration in ISO. Possible bindings for C [7] and ALGOL 68 [5] have also been proposed. A language binding for the PROLOG programming language is currently under development [9], and a draft version is being implemented within an enhanced version of the C-PROLOG interpreter [6] running on UNIX. GKS is designed to be implemented in the natural programming language of the host system and to have a language dependent layer as an interface to each of the other programming languages on the system. Our PROLOG implementation, therefore, forms an interface to a library of GKS functions written in the C programming language. Different PROLOG implementations may have different syntactical rules for differentiating between variables and atoms. The convention adopted in this binding document is that adopted by the C-PROLOG interpreter. Variables start with an upper case letter or an underscore, atoms start with a lower case letter or may be any string enclosed within single quotes. The draft ANSI standard GKS document [1,3] specifies guidelines for language bindings. These essentially constrain a binding, in effect, to provide a one-to-one mapping of GKS abstract functions to atomic language functions, and to specify data types corresponding to the GKS abstract data types. The rules also require the binding to observe good software engineering principles, a requirement which we