Ian, `oh` is indeed unbound inside the call to `call/cc`.
`oh` is only bound within the body of the `lambda` that is on the right-hand side of the `letrec`; it is not bound in the body of the `letrec`, which is where the call to `call/cc` is. I don't have my copy of TSS handy. Did you make a mistake while transcribing the program? Vincent On Tue, 08 Nov 2016 12:48:14 -0600, Ian Thomas wrote: > > Hello list, > > I've been working through The Seasoned Schemer and have come across code that > I can't access in the Racket REPL: specifically, the version of rember1* > shown on p. 139 of the 17th chapter. > > I'm not sure why there is a complaint about the 'oh' variable being unbound > in the last let form. > > Any suggestions/explanations would be most welcome. > > > Geiser error message. > racket@> ,enter > "/Users/ian/src/Scheme/books/the_seasoned_schemer/017_we_change_therefore_we_are.rkt" > 017_we_change_therefore_we_are.rkt:226:28: oh: unbound identifier in module > in: oh > context...: > /Applications/Racket v6.6/collects/racket/private/more-scheme.rkt:261:28 > standard-module-name-resolver > /Users/ian/.emacs.d/geiser/scheme/racket/geiser/user.rkt:54:0: enter! > /Applications/Racket v6.6/collects/racket/private/misc.rkt:88:7 > > Dr. Racket message. > oh: unbound identifier in module in: oh > > > Below is the code. > ;;rember1* > > (define rember1* > (lambda (l a) > (letrec ([R (lambda (l oh) > (cond > [(null? l) > (oh (quote no))] > [(atom? (car l)) > (if (eq? (car l) > a) > (cdr l) > (cons (car l) > (R (cdr l) > oh)))] > [else > (let ([new-car (call/cc oh > (R (car l) > oh))]) > (if (atom? new-car) > (cons (car l) > (R (cdr l) > oh)) > (cons new-car > (cdr l))))]))]) > (let ([new-l (call/cc oh > (R l > oh))]) > (if (atom? new-l) > l > new-l))))) > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
