[racket] metacircular interpreter, lexical scope, environment

On Wed, Dec 1, 2010 at 5:25 PM, David Van Horn <dvanhorn at ccs.neu.edu> wrote:
>
>
> An evaluator can implement function application using substitution, i.e.
> you can evaluate ((lambda (x) e) v) by evaluating the substitution of v for
> x in e.
>
> Or, you can be lazy and defer the substitution.  In that case, you evaluate
> ((lambda (x) e) v) by evaluating e; you just have to remember that v should
> have been substituted for x should you ever get to evaluating x.  The data
> structure you use to remember those deferred substitutions is an
> environment.  A simple list of variable, value pairs is a suitable
> representation.
>

Thanks - I have read the substitution part of PLAI and thought of using
substitution as well, but it seems that substitution does not constitute the
full solution:

   - it only work with side-effect free code
   - it does not address closure

Maybe I am looking too far ahead, but it seems like I cannot get away from
needing my own call stack?  Or am I missing something?

Thanks,
yc
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