I'm trying to write a macro that will turn a list of hex literals into a 
byte string.

(hex a b c 1 2 3) ; #"\n\v\f\1\2\3"

After many hours I have finally come up with this:

#lang racket
(define-syntax hex
  (syntax-rules ()
    [(_ num ...)
      (let ([e (syntax-e #'num)])
        (if (number? e) num
            (string->number (symbol->string e) 16))) ...)]))

(hex a b c 1 2 3)

Of course there are many issues with checking the parameters etc. My 
problem is this generates "a: unbound identifier in: a" because the 
arguments are evaluated? If I remove the last line it works in the REPL OK.

I suspect this is a small matter of my phases being mixed up, or a 
misunderstanding of when macros can be defined and used, or just outright 
ignorance on my part. I couldn't find any clues in the many, many 
references and tutorials I have read. I want to master them but I loathe 
creating macros, they always make me feel like an idiot, and I hope Racket2 
simplifies them somehow.

Thanks for any help sorting this one out.

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