[racket] Thought about namespaces

From: Jos Koot (jos.koot at gmail.com)
Date: Sun May 26 13:43:12 EDT 2013

#| Consider: |#
#lang racket
(define (get-from-fresh-namespace var)
 (let ((namespace (make-base-empty-namespace)))
  (parameterize ((current-namespace namespace))
   (namespace-require 'racket)
   (namespace-variable-value var #t (λ () 'error)))))
 (get-from-fresh-namespace 'add1)
 (get-from-fresh-namespace 'add1)) ; -> #t
 (get-from-fresh-namespace 'force)
 (get-from-fresh-namespace 'force)) ; -> #f
It is clear to me why the last form produces #f. Procedure force is a
predicate of a struct and is exported by module
.../collects/racket/promise.rkt. For each fresh empty base-namespace the
form (namespace-require 'racket) uses a distinct instance of this module.
Each instance defines the promise-struct freshly and provides distinct
variable- and syntax-bindings related to promises. Is my observation
It is little bit confusing that procedure get-from-fresh-namespace, when
called with the same variable-name, in some cases returns identical values
and in others does not.
I think it is not easy to make Racket such as to make it procedure
get-from-fresh-namespace always to return distinct objects (not eq?) or
always to return identical objects (eq?) when called with the same
I know, I am comparing procedures, but as
|# (let ((a add1)) (eq? a add1)) #|
is guaranteed to return #t, I wonder what you folks think about to make
modules such as always provide the same instance of a module when required
within the same Racket or DrRacket session. Is it possible? Is it desirable?
What when a module produces side effects (e.g. displayed output)?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20130526/8ebc6a13/attachment.html>

Posted on the users mailing list.