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 racket-users+unsubscr...@googlegroups.com. > 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 racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
