Subtext

Abstract

Representing programs as text strings makes programming harder then it has to be. The source text of a program is far removed from its behavior. Bridging this conceptual gulf is what makes programming so inhumanly difficult -we are not compilers. Subtext is a new medium in which the representation of a program is the same thing as its execution. Like a spreadsheet, a program is visible and alive, constantly executing even as it is edited. Program edits are coherent semantic transformations.The essence of this new medium is copying. Programs are constructed by copying and executed by copy flow: the projection of changes through copies. The simple idea of copying develops into a rich theory of higher-order continual copying of trees. Notably absent are symbolic names, the workhorse of textual notation, replaced by immediately-bound explicit relationships. Subtext unifies traditionally distinct programming tools and concepts, and enables some novel ones. Ancestral structures are a new primitive data type that combines the features of lists and records, along with unproblematic multiple inheritance. Adaptive conditionals use first-class program edits to dynamically adapt behavior.A prototype implementation shows promise, but calls for much further research. Subtext suggests that we can make programming radically easier, if we are willing to be radical.Text is paper-centric: pen and paper are a complete implementation. Modern software technology allows us to create arbitrary computer-based media, free of the limits of paper. A program can be represented in an abstract data model, and the programmer can use a GUI to directly manipulate [33] that model: WYSIWYG programming. This has long been done with other complex information artifacts, such as spreadsheets, documents, and diagrams. In all these cases, we no longer expect a paper printout to be a complete representation. It is time to transcend paper-centric programming.

Technical Dimensions of Programming Systems

“…Concrete examples of systems appear throughout the paper. Recent systems which motivated some of our dimensions include Subtext [17], which combines code with its live execution in a single editable representation; Sketch-n-sketch [38], which can synthesize code by direct manipulation of its outputs; Hazel [69], a live functional programming environment with typed holes to enable execution of incomplete or ill-typed programs; and Webstrates [50], which extends Web pages with real-time sharing of state.…”

Foundations of a live data exploration environment

“…"extract variable" has no effect on the result; "change constant value" forces recomputation of subsequent code). This can be elegantly implemented using bi-directional lambda calculus [43], but it also makes us consider more human-centric abstractions [14,15] further discussed in appendix D.…”