Class 34: Implementing LISP

Held: Monday, 25 April 2011

Summary: Today we continue to explore the techniques used to implement Lisp.

Related Pages:

• EBoard.
• Reading: Graham, Paul. (2002). The Roots of Lisp..

Notes:

• 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 should implement quote but 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.

Overview:

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

Quoting

• A few of you asked why we didn't do more quoting in CSC151. Here's the example I tend to give of how quoting confuses students.
• What do you expect for each of the following:
  • (symbol? (car '('a))
• (caar '('a))

Eval, Continued

• We'll continue our translation of eval into pseudo-Scheme.
• The legendary label.

Flaws

• Graham mentions two significant flaws in McCarthy's definition.
• What are they?
• How hard will they be to resolve?
• Sam's contrived scoping example

  ((lambda (x)
    ((lambda (f x) (f x))
     (lambda (y) (cons x y))
     a))
   b)
  

  vs.

  ((lambda (x)
    ((lambda (f z) (f z))
     (lambda (y) (cons x y))
     a))
   b)
  

Detour: Graham's Claims

• Graham claims that other languages (median languages) are getting closer to Lisp.
• Graham also claims that eval is central to what makes Lisp Lisp.
• What does he mean by these claims.

Implementing Lisp

• What does all of this say about the ease or difficulty of implementing Lisp?
• In particular, what do you need to write (in assembly or C or ...)?