A catch and throw example

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Lecture 3 - Page 24 : 43

Programming Paradigms
Simulation of other Paradigms and Continuations

A catch and throw example

We now give a Common Lisp like example of catch and throw.

Exit from a list length function in case it discovers a non-empty tail of the list

(define (list-length lst)
  (catch 'exit
    (letrec ((list-length1
               (lambda (lst) 
                 (cond ((null? lst) 0)
                       ((pair? lst) (+ 1 (list-length1 (cdr lst))))
                       (else (throw 'exit 'improper-list))))))
       (list-length1 lst))))

An example using catch and throw. Please notice that the example is not a proper Scheme program. Catch and throw are not defined in Scheme.

Same example with call-with-current-continuation

catch and throw are not available in standard Scheme