On Visible Programming

Tagged as programming, strangeloop

Written on 2012-09-26 20:13:00

I have a bad feeling that I'm about to piss off a lot of people. Oh, well.

Bret Victor gave a very interesting talk at Strange Loop called "Visible Programming". From what I can tell, Bret is a very smart guy and an accomplished UI designer. I was surprised to find that while I agreed with many (all?) of his premises I disagreed with most of his argumentation. As I've received a question or two about it, I'll try to clarify my thoughts here.

I have three core points:

  1. His vision requires reflection and an editor is the wrong place for it.
  2. Many examples were domain-specific and/or trivial but he didn't talk about general editor extensibility.
  3. Much he suggests is already done or can be done with some solid effort and available technology.

On Relective Systems

Ironically, I gave a talk on a different but overlapping topic a few weeks back. As mentioned in Chris Granger's talk, examples like the ones he and Bret Victor gave are much easier when working with a dynamic runtime. Unfortunately, dynamic is conventionally interpreted as a language with dynamic types and, put simply, we should try to change that. I argue that a dynamic language is one that allows you to inspect values and update function and class definitions while the program runs. This is formally known as reflection. What I believe dynamic language advocates care about is the ability to work with a "live" system, not the presence or lack of static type checking.

Being able to visualize program execution means having a snapshot of the program state during each step of execution. Setting aside the impractical size of such a thing for programs with arbitrarily large working data sets, this requires either A) annotating every line or function call with logging statements/function tracing, or B) instrumenting the language runtime in some fashion to retrieve values during execution. That's why these examples are much easier with a reflective language like Javascript where you can hook arbitrary behavior into the Object prototype.

Trying to get an editor to do this for all languages is a fool's errand without a nice reflective runtime and API to retrieve data from. It's hard enough with that stuff! And that means we need reflective compilers and interpreters before we can have an ideal editor.

On Editor Extensibility

Many of Bret's examples were highly domain specific. While it makes sense to have a simple interface for toying with values in a visualization/drawing program, it's harder to see how to usefully apply that to something like protein folding software or even RSS feed parsers. Having editor extensibility in addition to reflective systems enables arbitrary widgets or modes for dealing with a given problem domain or data visualization need. Plain and simple, there's no way to build-in useful visualizations that are universally applicable. I admit I am not a designer or gifted at visualization so I may have simply struggled here.

What can be done today

Bret essentially wants to make the experience of programming more tractable through interactivity and tangibility. He suggested 5 key requirements:

  1. Enable the programmer to read the vocabulary.
    • Mouseovers/tool-tips on all source tokens is largely available today and seems to address this.
  2. Enable the programmer to follow the flow.
    • A visualization to step through execution could be written somewhat easily given something like Common Lisp's trace.
  3. Enable the programmer to see the state.
    • This is essentially a more elaborate visualization that requires a bit more trace data than the above.
  4. Enable the programmer to create by reacting.
    • Suggests that editor not only autocompletes function names but default values too so you can see their effect immediately.
    • Function name autocompletion exists in many IDEs. Pervasive default values are easier for typed than "untyped" languages. Still requires runtime support!
  5. Enable the programmer to create by abstracting.
    • Essentially demonstrated a refactoring system here. Keep feeling like I missed something key about his argument.


While philosophically well-formed, Bret seems to miss the fact that runtime support is required for a Visible Editing Experience to emerge. If the industry still doesn't understand that dynamism is about the runtime rather than types, clamoring for a magic editor will get us nowhere. I want to see a more interactive, tangible environment in the future as well but we cannot get there by arguing that IDE/editor writers need to step up their game. We need to make a concerted argument for the resurrection of highly reflective systems in both research and industry. Once systems with robust reflective capabilities are widespread, realizing a vision such as that described will be a week long hack rather than a decade-long million man-hour slog.

I'd also like to examine how far reflection can scale and a bit about making such a thing applicable to both novices and experts but I need more time to compose my thoughts so I'll save that for a future post. Any comments on this post or its mistakes, of course, are welcome.

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