C311 Assignment 5 -- Introduction to Scheme++

Due Monday, February 13th, at 8:55 AM

Read and study carefully the introduction to Scheme++ for C311. Your comments on this introduction are especially welcome. The copper:/u/c311/bin/scheme script should be fixed today to support Scheme++.

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The code for the introduction's lambda calculus example is in copper:/u/c311/ss/lambda.ss. Extend this code to incorporate a substitute method in the classes derived from the syntax class in the same manner as the original classes derived from the syntax class were extended to include rename methods. You will need to redefine the class <syntax>. Also define a <lit> class for numeric literals that is a syntax class and extend the parser to recognize numeric constants (self-evaluating literals). Define global generics for the substitute and unparse methods so they can be used as indicated in the transcript of EOPL Exercise 4.2.3 (except that gensymed values will print differently).

> (unparse (substitute (parse '(lambda (a) (a (b 3))) (parse '(a 5)) 'b)))
(lambda (#:g0) (#:g0 ((a 5) 3)))

Hint: Define a free? method in each new class. Since this method is not a part of the problem specification, it should not be public.

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