Ok thanks for the explanations. I'll try doing one of the last two suggestions.
On Wed, Oct 2, 2013 at 4:09 PM, Ryan Culpepper <ry...@ccs.neu.edu> wrote: > No, the 'racket/pretty' module might be declared even if the symbol isn't > defined (or "mapped") in the namespace: > > > (define ns (make-base-namespace)) > > (define repl-ns (current-namespace)) > > (parameterize ((current-namespace ns)) > (eval '(require (only-in racket/pretty)))) > > (parameterize ((current-namespace ns)) > (namespace-attach-module repl-ns 'racket/pretty)) > namespace-attach-module: a different module with the same name is > already in the destination namespace > module name: "/opt/racket-5.3.6/collects/racket/pretty.rkt" > context...: > /opt/racket-5.3.6/collects/racket/private/misc.rkt:87:7 > > And the symbol can be defined in the namespace even if the module is not > declared: > > > (define ns (make-base-namespace)) > > (define repl-ns (current-namespace)) > > (parameterize ((current-namespace ns)) > (eval '(define pretty-print-handler #t))) > > (parameterize ((current-namespace ns)) > (namespace-variable-value 'pretty-print-handler)) > #t > ;; but racket/pretty is not declared, > ;; and #t is not a good print handler > > Ryan > > > > On 10/02/2013 03:58 PM, Stephen Chang wrote: >>> >>> A namespace is a mapping from top-level identifiers to whatever they are, >>> as >>> well as a separate mapping from module names to modules (roughly). What >>> you >>> care about here is the second mapping, but you're checking the first with >>> the patch. >> >> >> Thanks for the explanation. That helps a lot. So the danger with my >> check is when someone has another definition of pretty-print handler >> but racket/pretty has not been attached? >> >> But given the context, ie the dynamic require on the next line, it >> seems like there's already an assumption about what the identifier I'm >> checking is, so in this specific situation, isnt my check sufficient? >> >> >> >>> >>> Robby >>> >>> >>> On Wed, Oct 2, 2013 at 2:45 PM, Stephen Chang <stch...@ccs.neu.edu> >>> wrote: >>>> >>>> >>>>> Whether that identifier exists in the namespace has nothing to do with >>>>> whether racket/pretty can be attached. >>>> >>>> >>>> Can you explain this a little more because it's a little unintuitive to >>>> me? >>>> >>>> >>>>> >>>>> One option would be for install-pretty-printer! to just catch and >>>>> discard >>>>> the error. Evaluators for some languages would mysteriously not have >>>>> pretty-printing turned on by default. >>>>> >>>>> Another option would be to attach racket/pretty before requiring the >>>>> initial >>>>> language for the namespace. >>>>> >>>>> Another option is use #:pretty-print? #f when attaching racket/pretty >>>>> would >>>>> fail. >>>>> >>>>> Ryan >>>>> >>>> _________________________ >>>> Racket Developers list: >>>> http://lists.racket-lang.org/dev >>> >>> >>> > _________________________ Racket Developers list: http://lists.racket-lang.org/dev
