On 06-01-2023 14:31, yarl baudig wrote:
>>
>> That is also my understanding, confirmed by
>>
>> $ cat lib.scm
>> (define-module (lib)
>>     #:export (test))
>>
>> (define-syntax test
>>     (lambda (sintax)
>>       (syntax-case sintax ()
>>         ((test id)
>>          (datum->syntax sintax (free-identifier=? #'id #'thing))))))
>> [...]
>>
> 
> Thank you both. I am trying to process this. I (re-)read 6.8 Macros and read tspl4. I don't understand why you use "datum->syntax" > I heard your suggestion. I am only trying to grasp things for now. I 
realize I don't know enough (on guile and on guix) to go on a concrete 
goal yet.
> I need to work more on this in order to understand but I wanted to thank you for answering that quickly!
free-identifier=? returns a boolean.  However, the return value of the 
clauses of the syntax-case must be a syntax object.  Hence Jean 
converted the boolean into a syntax form with datum->syntax (IIUC).

Guile's implementation of macros is a little lax with typing,
in the sense that objects like #false and #true (but not symbols, 
because hygiene) can be returned too, but IIUC this is undocumented and 
not standard Scheme (*).

(*): unverified

Greetings,
Maxime.