COSC 152 Programming Languages
Fall 2007
Homework Assignment #6
Bindings and Closures
Due: Friday, Oct 26, 12:00PM CDT
Submit: E-mail electronic
copy to professor, with a subject header "COSC 152 HW#6".
Work may be completed in pairs. Each team should submit only once. Be
certain to put both team member names on work submitted. It would be
courteous to carbon-copy your partner when e-mailing the final
submission.
The Grammar
For this assignment, extend the grammar from
HW #5
to include the following productions:
<expr> |
   ::=    |
( let ( { ( <id> <expr> ) }* )
<expr> ) |
Add primitive operators cons, car, cdr,
list, empty-list, and empty?.
Parser
Use the SLLGEN parser generator system to specify your lexical and syntax
rules, and automatically build your
parse function.
Modify your existing unparse function to work with the new
abstract syntax and parse function.
Interpreter
Modify your
evaluate function to operate over the new syntax,
and enable
lambda expressions and applications.
Notes:
Introduce an abstract data type to represent closures, as
discussed in lecture. Check for proper numbers of parameters when
applying a closure to its arguments.
Introduce an abstract data type to represent general S-Expressions
of the type manipulated by cons, car, cdr,
and list. The empty-list primitive takes no arguments,
and should return your abstract data type for an empty list. The
empty? predicate evaluates to true if and only if
its argument is an empty list, false otherwise.
Check rigorously for errors in the input, or for invalid expressions.
Appropriate errors should be thrown if your interpreter
encounters any trouble. See the eopl:error construct
used in the text. Think carefully about what kinds of errors the
interpreter can encounter.
Here's an excellent testcase once your interpreter is fully functional:
>
(run "((car (car (cdr (list (lambda (x) (add x 1))
(cons (lambda (y) (mul y 2))
(lambda (z) (mod z 3))) ))))
(let ((x 5) (y 10) (z 20))
(if (lesser y z)
(div 100 y)
(sub 100 x))))")
> 20
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[Revised 2007 Oct 17 20:38 DWB]