Whoa, how do you mean?

One idea I've been thinking about a lot is to attach metadata to code. We can do a lot to code (pretty-print, optimize, ...) besides just eval it, and metadata might help with those without affecting eval.

My favorite use for this idea is to give functions levels:

  def (foo x y) :(level 3)
    34

This can be used in a variety of ways by different tools. You could flag as errors any calls from a lower to a higher level, so that level 3 functions could only call functions in levels 1-3. You could tell tracers to trace everything until level x, not below. You could tell debuggers to automatically step past calls below level x and step _into_ calls above that level. In gdb I often accidentally hit 'next' when I meant 'step', and now I have to restart and laboriously try again from scratch.

You could syntax-highlight calls within a level to be more salient to calls to lower levels. We've all seen open source projects with this structure.

  void main() {into 
    ...  // lots of option parsing crap
    if (doSomething()) { // the actual app code
       ... // more crap
    }
    ... // more crap
    return -1;
  }

In general, syntax highlighting sucks[1] because we simply highlight the things it's easiest to infer. Metadata might help reduce the inference burden and open up new uses for color.