Problems with macro-defining macros

[Luis Casillas <luis at casillas dot org>]

Following Kjetil and Per's discussion, I tried the experiment below,  
but I can't get it to work (I've tried it only in the REPL).  I did  
manage to get a trivially modified version of it to work in PLT  
Scheme 360 (changes in comments).


(define (alter-syntax-datum proc stx)
  ;; must use define-syntax-datum in PLT
  (datum->syntax-object stx (proc (syntax-object->datum stx))))

(define-syntax define-symbol-altering-macro
  (syntax-rules ()
    ((_ (macro-name arg) expr . exprs)
     (define-symbol-altering-macro macro-name (lambda (arg) expr .  
exprs)))
    ((_ macro-name proc)
     (define-syntax macro-name
       (lambda (stx)
         (syntax-case stx ()
           ((_ sym . args)
            (let ((new-sym (alter-syntax-datum proc (syntax sym))))
              ;; must use #, in PLT
              #`(,new-sym . args)))))))))

(define-symbol-altering-macro (call-reversename sym)
  (string->symbol
   (list->string
    (reverse
     (string->list
      (symbol->string sym))))))

(call-reversename yalpsid 50)
=> <stdin>:40:1: circular list is not allowed after #<syntax mys in  
#171>