Arrays of characters are a basic data type in many programming languages, but strings and substrings are seldom accorded first-class status as parameters and return values. Such status would enable a routine that calls a search function to readily access context on both sides of a return value. To enfranchise substrings, this paper describes a new data type for substrings as a special case of one for general subsequences. The key idea is that values are not sequences or references to positions in sequences, but rather references to subsequences. Primitive operations on the data type are constants, concatenation, and four new functions— base , start , next , and extent —which map subsequence references to subsequence references. This paper informally presents the data type, demonstrates its convenience for defining search functions, and shows how it can be concisely implemented. Examples are given in Ness, a language incorporating the new data type, which is implemented as part of the Andrew User Interface System.

Users of interactive systems typically must deal with numerous interactive interfaces, including especially the text editor and the system command interpreter. Unfortunately, the various interfaces too often have differing and even conflicting conventions. This paper suggests that an enhanced text editor can serve as the interactive interface for most purposes. For example, consider the file directory instead of choosing among half a dozen or more system commands to view and modify it, the user can edit an image that represents the directory. Deletion, renaming, and movement to another directory are easily accomplished with ordinary editor commands. Other system commands can he supplanted by a mechanism of "creation sequences" for files. Rather than execute the creation sequence, the user simply asks to view the file resulting from it.To facilitate this form of interaction, the text editor must include some novel features. It must permit structured files; where the structure can be a field structure within records or a hierarchical structure between records. A suitable editor is sketched.