[plt-scheme] continuing to write newbie notes on units; feedback?

Hi everyone,

I'm still trying to write a tutorial on Units for people who've never seen
them before.  Here are the state of the notes now:

    http://hkn.eecs.berkeley.edu/~dyoo/plt/unit-notes.text

I finished writing a section on treating units as functors.  This has to
be obvious to everyone else, but for folks who haven't had much experience
with ML-style functors, this is exciting stuff.  *grin*

I'm about to start diving into the use of units in others parts of the PLT
Scheme system, and would like some suggestions before I jump in too
deeply.  I think the next part I'll need to cover is signed units, but
we'll see... I want to jump into how units are applied in PLT Scheme as
soon as I can.

Is there anything in the notes that I have so far that need elaboration,
or anything that is just wrong and needs correction?



Also, I did have a question about mixins; are they intrinsically tied to
units still?  I got that impression from the paper "Modular
Object-Oriented Programming With Units and Mixins", but from the class.ss
documentation,

http://download.plt-scheme.org/doc/299.100/html/mzlib/mzlib-Z-H-4.html#node_sec_4.6

it sounds that lambda is sufficient to construct mixin classes
parameterized on the superclass.  I'm still a little confused on this
point.



Thanks for any help!