[e-lang] Need help with program analysis for Transparent auditor (or: code zippers)

[David-Sarah Hopwood]

Kevin Reid wrote:
> I've thought of two possible solutions so far:
> 
> 1. Starting from EMethod(..., "a", ...), scan its children for  
> occurrences of NounExpr("foo") and reject any which bind it. This  
> would reject more than it needs to.
> 
> 2. Switch to a pre-processing stage (instead of the incremental  
> operation of a zipper) to assign an identity (or a mutable analysis- 
> information field, equivalently) to each variable binding and all of  
> its uses, and add upward references (like in the zipper) to each  
> node; this would make the is-this-foo-that-foo test a simple comparison.
> At the moment, the second option seems attractive; tying uses to  
> definitions of variables in a generic fashion should be useful for  
> other types of analysis. And since this is strictly analysis, not  
> transformation, I don't need the modify-without-mutation function of  
> a zipper. The only reason I haven't done that yet is I think zippers  
> are neat (and there might be other uses for an established zipper  
> over E ASTs).

The second option is called "Barendregt's convention". It's very common
to use this convention in program analysis; you would be in good company.

-- 
David-Sarah Hopwood