CSC302 2011S, Class 34: Implementing LISP

Overview:
* Detour: Quoting.
* eval, continued.
* Flaws in eval.
* Graham's Claims.
* Implementing Lisp.

Admin:
* Easter weekend consumed my time.  I'm not sure when I'm getting grades to you.
* Those of you who missed one assignment may make up for it by implementing a simple LISP interpreter in C (basically, writing the parser and the N or so key functions).  For the parser, you need not implement the shorthand of '.
* Reading for Wednesday: Trail: The Reflection API, available at 
  http://download.oracle.com/javase/tutorial/reflect/
* Reminder: Projects start Friday.
* Due to prereg and College committee work, I need folks to sign up for appointments.  Times at http://www.cs.grinnell.edu/~rebelsky/Schedule/signup.2011S.txt.  Signup via email.
* CS Picnic: Friday, May 6, 2011.
* EC for Thursday's Bites to Bits.
* EC for Friday's CS table.

Detour: Quoting.
* Why we don't teach it in 151: It's more complicated than you think
* Important lessons on high-level syntax, undelrying representation, and
  interpretation.

eval, continued.
;;; Procedure:
;;;   eval
;;; Parameters:
;;;   expression - to be evaluated
;;;     An atom or list: S-expression
;;;   environment - binds values to names
;;;     Association list: A list of (symbol value) lists
;;; Purpose:
;;;   Returns the value of the expression in that environment

An S expression is either:
* an atom
* a pair of two S expressions

A list is a form of S-expression in which the cdr of the last pair in
the sequence is NIL.

* Flaws in eval.
* Graham's Claims.
* Implementing Lisp.