Hello!
This is a follow-up to the excellent answer by Alex Knauth on StackOverflow
here: http://stackoverflow.com/a/38032107/324969 and this mailing-list thread:
https://groups.google.com/forum/#!topic/racket-users/sS-pUUGp9o4
I'm trying to write a module meta-language mylang, which accepts a second
language to which is passes the modified body, such that:
(module foo mylang typed/racket body)
is equivalent to:
(module foo typed/racket transformed-body)
The real-world goal is to transform the fully-expanded body (e.g. add a
submodule, like the "doc" module added by scribble/lp2).
Alex came up with the implementation below. It puts the body into a dummy
module, fully expands it, and extracts the (#%plain-module-begin . mod-body),
patching it to require the user-provided lang. This works very well in all
cases except when the body contains submodules.
In that case, I get an "require: namespace mismatch; reference to a module that
is not available" error.
I'm rather clueless about how to solve that problem. I tried using local-expand
with a 'module-begin context, but it then complains that x is unbound when the
user-supplied language is typed/racket, and the error seems to be related to
the submodules generated by TR.
Any suggestions?
Georges Dupéron
#lang racket
;; The language definition
(module mylang racket
(provide (rename-out [-#%module-begin #%module-begin]))
(define-syntax (-#%module-begin stx)
(syntax-case stx ()
[(_ lng . rest)
(with-syntax ([#%module-begin (datum->syntax #f '#%module-begin)])
;; put the code in a module form, and fully expand that module
(define mod-stx
(local-expand
#'(module ignored lng (#%module-begin . rest))
'top-level
(list)))
;; pattern-match on the #%plain-module-begin form to insert a require
(syntax-case mod-stx (module #%plain-module-begin)
[(module _ lng (#%plain-module-begin . mod-body))
#`(#%plain-module-begin
(#%require lng)
.
#,((make-syntax-introducer) #'mod-body))]))])))
;; A module using that language
(module foo (submod ".." mylang) typed/racket/base
(module a-submod typed/racket/base
(define x 1)
(provide x))
(require 'a-submod)
(ann (+ x 1) Number))
(require 'foo)
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