2939	 Abstraction Mechanisms in CLU	 CLU is a new programming language designed to support the use of abstractions in program construction. Work in programming methodology has led to the realization that three kinds of abstractions-procedural control and especially data abstractions-are useful in the programming process. Of these only the procedural abstraction is supported well by conventional languages through the procedure or subroutine. CLU provides in addition to procedures novel linguistic mechanisms that support the use of data and control abstractions. This paper provides an in troduction to the abstraction mechanisms in CLU. By means of programming examples the utility of the three kinds of abstractions in program construction is illustrated and it is shown how CLU programs may be written to use and implement abstractions. The CLU library which permits incremental program development with complete type checking performed at compile time is also discussed. programming languages data types data abstractions control abstractions programming methodology separate compilation
