[plt-scheme] metaphors for local

Matthias Felleisen wrote:

> Most of what you have mentioned is flawed.

I'm sorry, I wasn't clear. I meant something with the metaphoric power 
of the stack of books for a stack, or the cache of books for a cache. I 
didn't mean that these metaphors applied to local. Anyone coming from a 
primarily imperative background will, if they are not careful, try the 
stack metaphor and screw it up. (Since Pascal went away, the amount of 
experience with lexical scope out there has diminished dramatically, 
even if gcc does support it, sort of.)

> I recommend to think of a pile of papers except that every programmer 
> has his own secret ink with which to definitions that only he can read. 
> Don't ever throw any of these papers away! You might need them.

Yes, but these papers are written at compile time and read at run time, 
and we don't have these notions when local is introduced in HtDP. At 
least we don't have mutation, either. --PR