The mechanism used to define the programming language PL/I in the recently adopted American National Standard is presented. This method provides a rigorous though semiformal specification of the language. If uses the model of translation of programs into an abstract form to define the context-free and context-sensitive syntax. The semantics are defined by the interpretation of the abstract form of the program on a hypothetical machine. The method and metalanguage are presented along with several small examples to illustrate the definition technique's features. The complete definition process is shown by the definition of a small example language.

Abstract A method of handling asynchronous interrupts, which are defined to be events, in a highlevel, block‐structured language is described. The language facilities are based on PL/1 conditions. The functions of an interrupt handler and its relationship with the execution time support for the language are defined and discussed. The development of the facilities being presented is also described. Solutions to design problems and implemenation details are stated. The use and benefits of the mechanism are discussed.

Abstract This paper reports on the design and development of a high level language, Malus, for use in implementing a time‐sharing system. Emphasized are the ways that the language and its compiler accommodate the specialized requirements of systems programming and programmers. Among these are the need to generate highly efficient object code, to allow inter‐programmer communication by program self‐documentation, and to define and organize system tables and data. In addition, the Malus compiler is highly modular; thus the language may be modified or augmented in response to user needs unforeseen during langauge design. Systems programs cannot be machine independent and Malus allows explicit control of emitted code when an application requires particular efficiency or use of privileged instructions. There is also a facility allowing nested redefinition of identifiers. Efficient storage management and data access is effected by the availability of based structures, a register storage class and built‐in functions to facilitate their use. Malus is evaluated both in terms of some general criteria for systems implementation languages and by an appraisal of user reactions. While this assessment shows a few areas where the language might be improved, it is felt that Malus is a valuable and effective tool for systems implementation.