Namespaces: APL/W vs. APL2

ABSTRACT

This paper describes and contrasts the implementation of namespaces in two popular combinations of APL dialects and platforms: IBM's APL2 (version 2, release 2) running under VM/CMS, and Dyadic's Dyalog APL/W (version 7.0) running under Microsoft Windows.In a traditional APL workspace, localization is the only mechanism available to isolate identifier names and values, and it is extremely potent. While a function that localizes a given name is executing, it is impossible to reference any other definition of the same name.Namespaces are a significant addition to an APL system. They provide a way to “package” a collection of objects (variables, defined functions, etc.), and insulate them from the traditional workspace. A namespace co-exists with the workspace, yet its object names and definitions are completely independent of the workspace. Namespaces can help to organize and hide complexity in workspaces, avoid name conflicts, and share code among applications.IBM has offered namespaces in APL2 since 1987, whereas Dyadic just recently introduced their facility. Both implementations provide encapsulation and name isolation within a workspace. But they use quite different methods to access objects in a namespace and store their initial definitions. The merits of each approach are discussed. An example is provided to illustrate how namespaces may be used to simplify the implementation and improve the functionality of workspace and function analysis tools.

REFERENCES

• 1: Dyalog APL for Windows {version 7.0}, Language Reference, Dyadic Systems Limited, 1994.
• 2: APL2 Programming: System Services Reference, Version 2 Release 2, IBM publication number SH21-1054-01, 1994.

INDEX TERMS

Primary Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.2 Language Classifications

          Nouns: APL

Additional Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.3 Language Constructs and Features
          Subjects: Control structures

  F. Theory of Computation
  F.3 LOGICS AND MEANINGS OF PROGRAMS
      F.3.3 Studies of Program Constructs
          Subjects: Functional constructs

General Terms:
Algorithms, Languages

Keywords:
localization, namespace, package