An Introduction to SequenceL: A Language to Experiment with Constructs for Processing Nonscalars

Abstract

SUMMARYSequenceL is a language intended for experimentation with declarative constructs for nonscalar processing. In SequenceL, a problem solver provides little in the way of iterativehecursive details in a problem solution. Instead, the problem solver describes the solution directly by specifying, via a metastructure, the data structures which will hold results useful for solving the problem. SequenceL is a small language (i.e. there is a small number of language constructs), and it is not domain dependent. This paper is meant to introduce the reader to SequenceL. KEY WORDS: software; automatic programming; software engineering; programming languages MOTIVATION AND BACKGROUND OF SEQUENCELThere currently exist several approaches to programming, including the imperative, functional, logical, and object-oriented paradigms. Arguably, these various approaches exist in order to accommodate different types of problem solvers. There does not appear to be a 'one size fits all' when it comes to paradigms. What appeals to one person may not appeal to the next.The purpose of this paper is to present a language, SequenceL (formerly called BagL). SequenceL is an experimental computer language. It is based upon a strategy for problem solving wherein one solves a problem by describing data structures strictly in terms of their form and content, rather than also having to describe the i terativehecursive detail to produce and/or process the data structures algorithmically. As with the other approaches to programming, SequenceL may not be for everyone, but it does represent another approach to problem solving. 1.1.From one perspective, the history of language design indicates that languages have evolved from algorithmic-oriented languages to data structure-oriented languages (see Figure 1). Consider the move from FORTRAN to languages like ALGOL and Pascal. In solving problems in FORTRAN, one focuses on the production of an algorithm. In a language like Pascal, a problem solution is an algorithm that interacts appropri- ately with a data structure. A good example of the Pascal view is a program to convert a prefix arithmetic expression into an equivalent postfix expression. After constructing a binary tree which holds the prefix expression in an appropriate configuration (that is, a configuration where operators are parents of operands), one merely performs a postorder traversal of the tree to obtain the postfix expression. The data structure designed thus plays a central role in the problem solution. Object-oriented languages, which encapsulate data structures, take the notion of problem solving further away from algorithms and closer to data structure design. The intent is to view the product of software engineering to be a set of objects, rather than programs.SequenceL has been developed in order to explore the possibility of a language based solely on high-level constructs for describing data structures. In SequenceL, a problem solution is a data structure which holds results useful in solving some problem. This view of a data...

Architecture and Design Modeling and Simulation Testbeds for NASA: A Progress Report

“…The SequenceL language [13,14,15,16] is a Turing-complete executable requirements language. We are currently using it to develop the Shuttle Abort Flight Management System requirements (SAFM).…”

Automatic parallel control structures in SequenceL

“…SequenceL is based upon three constructs for processing nonscalar structures [4,5]. The three constructs are the regular, irregular, and the generative constructs.…”

“…Two singletons: +( [4,4]) = [8] Non-scalars: +( [4,4,3,2]) = [13] Nested: +([ [10,20,30,40,50], [4,5,6,7,8]]) = [14,25,36,47,58] In all cases these operations execute in a uniform way: the operator is applied to corresponding elements of the normalized operand sequences. In the examples above normalization has no effect.…”

“…. , n], [2,3,4,5] The multiplication operation will apply to each ith element of the successor s 1; that element is an odd number. The values for i are obtained through the generation (see generative construct below) of the integers from 1 to n. The value for n, which is based upon the size of the successor element s 1, is obtained when the function begins execution.…”

“…The goal of the SequenceL language [4,5] is to provide an environment where problem solutions can be stated at a high level of abstraction-where one can describe the data product explicitly and have the iterative and parallel program structures that produce and process the data product generated automatically. In other words, the desire is for a language that is based upon high level constructs that permit one to declare data products directly.…”