Editing by example

An editing by example system is an automatic program synthesis facility embedded in a text editor that can be used to solve repetitive text editing problems. The user provides the editor with a few examples of a text transformation. The system analyzes the examples and generalizes them into a program that can perform the transformation to the rest of the user's text. This paper presents the design, analysis, and implementation of a practical editing by example system. In particular, we study the problem of synthesizing a text processing program that generalizes the transformation implicitly described by a small number of input/output examples. We define a class of text processing programs called gap programs, characterize their computational power, study the problems associated with synthesizing them from examples, and derive an efficient heuristic that provably synthesizes a gap program from examples of its input/output behavior. We evaluate how well the gap program synthesis heuristic performs on the text encountered in practice. This evaluation inspires the development of several modifications to the gap program synthesis heuristic that act both to improve the quality of the hypotheses proposed by the system and to reduce the number of examples required to converge to a target program. The result is a gap program synthesis heuristic that can usually synthesize a target gap program from two or three input examples and a single output example. The editing by example system derived from this analysis has been embedded in a production text editor. The system is presented as a group of editor commands that use the standard interfaces of the editor to collect examples, show synthesized programs, and run them. By developing an editing by example system that solves a useful class of text processing problems, we demonstrate that program synthesis is feasible in the domain of text editing.