Is there any function like 'try' in Racket

Question

Now I'm leaning schemer by looking the book The Seasoned Schemer. I writed the code by racket, however when I using the try, the schemer didn't have this method or macro. And It reported expand: unbound identifier in module in: try. The code as the below: (in the page 89)

(define (remove-member-first* a lat)
   (try oh (rm a lat oh) lat))

I've search the racket documents, but didn't find smiliar function.

So who does know whether there are kinda function like the 'try'?

Answer 1

I've just found someone who has already written all code snippets from the book The Seasoned Schemer in github.

And it is his answer: ( It is not non-hygienic and don't require other model)

(define-syntax letcc
  (syntax-rules ()
    ((letcc var body ...)
     (call-with-current-continuation
       (lambda (var)  body ... )))))


(define-syntax try 
  (syntax-rules () 
    ((try var a . b) 
     (letcc success 
       (letcc var (success a)) . b))))

The link is https://github.com/viswanathgs/The-Seasoned-Schemer

Answer 2

You don't mention it, but I'm guessing that the book you're talking about is "The Seasoned Schemer". Use the following macro definitions for implementing try as defined in the book:

(require mzlib/defmacro)

(define-macro (letcc c . body)
  `(call/cc (lambda (,c) ,@body)))

(define-macro (try x a b)
  `(letcc *success*
     (letcc ,x
       (*success* ,a))
     ,b))