Lucid, a nonprocedural language with iteration
Communications of the ACM
The next 700 programming languages
Communications of the ACM
Correct and optimal implementations of recursion in a simple programming language
STOC '73 Proceedings of the fifth annual ACM symposium on Theory of computing
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In this paper we describe how Lucid can be extended to allow user-defined functions and scope conventions, i.e. conventions for limiting the range or scope of the validity of definitions. This is done using new constructs called clauses which are similar in form to the blocks and procedure declarations of Algol-like languages, but are nevertheless strictly non-imperative, because a clause is actually a compound assertion, i.e. an assertion formed, as a program is, by combining a collection of assertions.Each type of clause (there are four) has a straightforward mathematical semantics together with its own characteristic "manipulation rules" for general program massage. In addition, the informal operational view of (some) Lucid programs (described in a previous paper) can be extended to give an (incomplete) operational understanding of the effect of the clauses. In this framework a "compute" clause defines a block; a "mapping" clause defines a conventional (pointwise) function; a "produce" clause defines a block with persistent memory (or an anonymous 'process' or 'actor'); and a "function" clause defines a sort of procedure with own variables (or a general kind of coroutine).