[plt-scheme] handle exception

Petros Pissias wrote:

 > I'm trying to make a programm that draws a function.
 > The only problem is that sometimes the function
 > throws a 'divide by zero exception' that must be handled correctly.
 >
 > The user is prompted to give the function  [example:  (lambda (x) (/ 1
 > x))]
 >
 > I don't want the user to give the exception handling details in the
 > function
 > [example: (lambda (x)
 >     (with-handlers ([exn:application:divide-by-zero?
 >                      (lambda (exn) +inf.0)])
 >       (/ 1 x)))  ]
 >
 > I'm trying to 'insert' the exception handling code after the "
 > (define func (read))" which reads the function,
 > but I can't get it right...

There is two options:

  1. Redefine /

   (define prim:/ /)
   (define (/ a b)
      (if (= b 0)
         +inf.0
         (prim:/ a b)))

   2. Insert the with-handlers form where you evaluate the user specified
      function

   > (define (tabulate f from to)
       (if (> from to)
         '()
         (cons (with-handlers ([exn:application:divide-by-zero? (lambda (e) +inf.0)])
                 (f from))
               (tabulate f (+ from 1) to))))
   > (tabulate / -2 2)
   (-1/2 -1 +inf.0 1 1/2)

-- 
Jens Axel Søgaard