Thanks for the responses. In case anybody is interested, I came up with the
following implementation. Since (at least in this simple implementation)
there is an obvious symmetry between explicit renaming and implicit
renaming I added the er-macro-transformer also. They seem to work
correctly. One minor difference to the ir-macro-transformer in Chicken
though is that parameters also need to be injected (which kind of logically
makes sense).
I am not exactly sure whether datum->syntax and syntax->datum go through
the entire expression but if they do, the implementation will be very
inefficient. (If anybody knows more on that, I would be interested.)
Implementation:
#lang racket
(provide (for-syntax ir-macro-transformer er-macro-transformer))
(begin-for-syntax
(require (for-syntax (only-in racket/base lambda syntax with-syntax)))
(define-syntax ir-macro-transformer
(lambda (stx)
(with-syntax ([(_ proc) stx])
#'(lambda (x)
(datum->syntax #'proc (proc (syntax->datum x) (lambda (v)
(datum->syntax x v))))))))
(define-syntax er-macro-transformer
(lambda (stx)
(with-syntax ([(_ proc) stx])
#'(lambda (x)
(datum->syntax x (proc (syntax->datum x) (lambda (v)
(datum->syntax #'proc v)))))))))
Examples:
; loop example from Shu-Hung's post is now working as expected
(define-syntax loop
(ir-macro-transformer
(lambda (expr inject)
(let ((body (cdr expr)))
`(call-with-current-continuation
(lambda (,(inject 'exit))
(let f () (begin .,(inject body)) (f)))))))) ; notice the
(inject body) here... dropping the inject will break the code
;=> 543210
; the following suggests that the lexical environments work as they should
(let ([x 1]
[y 2])
(swap! x y)
x)
=> 2
(define t 3)
(define-syntax tripple
(ir-macro-transformer
(lambda (expr inject)
(let ([a (cadr expr)])
`(* t ,(inject a))))))
(let ([t 29]
[* -])
(tripple 2))
;=> 6
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