Powerful editing systems for developing complex software documents are difficult to engineer. Besides requiring efficient incremental algorithms and complex data structures, such editors must accommodate flexible editing styles, provide a consistent, coherent, and powerful user interface, support individual variations and projectwide configurations, maintain a sharable database of information concerning the documents being edited, and integrate smoothly with the other tools in the environment. Pan is a language-based editing and browsing system that exhibits these characteristics. This paper surveys the design and engineering of Pan , paying particular attention to a number of issues that pervade the system: incremental checking and analysis, information retention in the presence of change, tolerance for errors and anomalies, and extension facilities.

The Program Dependence Web (PDW) is a program representation that can be directly interpreted using control-, data-, or demand-driven models of execution. A PDW combines a single-assignment version of the program with explicit operators that manage the flow of data values. The PDW can be viewed as an augmented Program Dependence Graph. Translation to the PDW representation provides the basis for projects to compile Fortran onto dynamic dataflow architectures and simulators. A second application of the PDW is the construction of various compositional semantics for program dependence graphs.

Processors for programming languages and other formal languages typically use a concrete syntax to describe the user's view of a program and an abstract syntax to represent language structures internally. Grammatical abstraction is defined as a relationship between two context-free grammars. It formalizes the notion of one syntax being “more abstract” than another. Two variants of abstraction are presented. Weak grammatical abstraction supports (i) the construction during LR parsing of an internal representation that is closely related to the abstract syntax and (ii) incremental LR parsing using that internal representation as its base. Strong grammatical abstraction tightens the correspondence so that top-down construction of incrementally-parsable internal representations is possible. These results arise from an investigation into language-based editing systems, but apply to any program that transforms a linguistic object from a representation in its concrete syntax to a representation in its abstract syntax or vice versa.