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ABSTRACT

Structured programming advocates the elimination of the GOTO from the set of primitives for a computer language. Yet at the machine language level, almost all machines offer only the conditional or unconditional branch as the basic control primitive. Vaughan Pratt has suggested using instead pseudo-non-deterministic programming (as well as the COMFY name). We present a new set of machine language control primitives based on Pratt's suggestion which are simpler to implement than if-then-else and do-while and are more flexible at the same time. The machine language implementation of these primitives requires nothing more complicated than a stack; the size of the stack needed (exclusive of programmer-defined subroutine control points) is O(d), where d is the operator depth of the program. This is much less space and machine complexity than would be required for a true backtracking control structure. The user can emulate if-then-else, do-while, repeat-until, etc., with macros using these primitives if he so desires.

INDEX TERMS

Primary Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES

Additional Classification:
  B. Hardware
  B.1 CONTROL STRUCTURES AND MICROPROGRAMMING
      B.1.4 Microprogram Design Aids
          Subjects: Languages and compilers

General Terms:
Design, Languages, Theory