The Definition and Implementation of Lsix in BCL

Lsix is a London version of the Bell Telephone Laboratories low-level list processing language L6 (Knowlton, 1966). This paper describes an implementation of Lsix using BCL, a general purpose programming language with special emphasis on data structures (Hendry, 1966). The BCL used is that denned by the prototype compiler which was available in January, 1967. Both the definition and the implementation are in BCL; the former is freely annotated but for those not familiar with BCL a few words of explanation are given in an Appendix. It is considered that the ability to define a language so precisely in this way is one of the interesting features of this paper. Lsix instructions are compiled into an intermediate code which is executed by a low-level interpreter. The definition is followed by an outline flow diagram of the interpreter and details of three general field handling routines to find fields, get fields and store fields. A complete Lsix program which has been run on the Atlas computer is given to illustrate the form of the data to be analysed. For a more detailed description of the language the reader is referred to Knowlton's description of L6.