Hello,
I am working on a project in which I am trying to implement a Common Lisp-style
package system. A simple example of usage would be as follows:
(in-package FOO
(define BAR 2))
; ...
(in-package FOO
(define BAZ (add1 BAR)))
; ...
(in-package FOO
(add1 BAZ)) ; => 4
; ...
(in-package QUUX
(add1 FOO:BAZ)) ; => 4
I was able to get something to this effect by doing the following:
1. Create a namespace during phase 1 for each package
2. Wrap the (in-package ...) body in a submodule
(to remove any local bindings in other parts of the file)
3. Wrap the body in the following:
(require (for-syntax syntax/parse) racket/splicing)
(parameterize ((current-namespace #,(package-namespace resolved-package)))
(splicing-let-syntax ((#%top (λ(stx)
(syntax-parse stx
[(_ . id) #'(namespace-variable-value 'id)]))))
#,@#'body))
This makes all non-local definitions resolve to the current namespace's
definition.
This works great. I ran into a problem, however, when trying to create a
provide transformer for the packages. I wrote the transformer and tried to test
it, only to be greeted by this message:
write: cannot marshal value that is embedded in compiled code value
The value in question was one of the namespaces I had created. Some searching
online led me to http://stackoverflow.com/questions/17437037/what-is-3d-syntax
, which, while telling me what the problem with my code was, still leaves me
wondering, is this a bad place for 3D syntax? More or less, I am trying to
manually link the identifiers in a given environment and export those bindings
as runtime values. Is there another/a better way to do this? While I could
perhaps shoehorn these namespace bindings into purely phase 0 code, I would
rather have more preprocessor overhead and less runtime overhead and link
everything up during phase 1*. If that's a reasonable idea, how might I go
about pushing these namespace values from phase 1 to phase 0?
*Disclaimer: There's a decent chance that any such "placement" of the overhead
is a figment of my imagination and, in reality, pushing it to phase 0 will make
no difference.
Regards,
- Philip Blair (belph)
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