[plt-scheme] And now for an actual Scheme question (PLAI)

You're a dangerous man, Prabhakar!

I *am* going to excom you now.  Gregory seems to have enough on his
hands.  You're having him go off-track in a Land Rover without knowing
whether he knows how to fix a boiling radiator, shift into 4WD, or use
a hitch to pull himself out of a flooding gully.  That's
irresponsible.

Gregory:

I would suggest that you:

- download the PLAI add-on (available from the book's home page, and
  tested for 4.x)

- use the book's notation

- get on with writing *interpreters* and stop worrying about parsing

After you get the initial parser working (as you have), you will add
at most one line to the parser per chapter, and that line will mostly
be a copy-and-paste job.  So worrying about parsing won't get you
anywhere.  In contrast, using TYPE-CASE will find several bugs for you
(as Eli has nicely described) and help you focus on the
right-hand-sides.  Yes, MATCH will do the same, but

- you don't get as much static checking

- you've veered off from the book: you can no longer just copy code
  from the book and try it out

If you get through half the book and find that you're nailing all the
conceptual material and the interpreters, and your *single biggest
problem* is dealing with s-expression syntax, you can use Prabhakar's
MATCH suggestion.  But not before then.

Yellow card for you, Prabhakar.

Shriram