On 03-08-2022 11:12, Damien Mattei wrote:
> scheme@(guile-user)> (define str2 "hello")
> scheme@(guile-user)> (string-set! str2 4 #\a)
> ice-9/boot-9.scm:1669:16: In procedure raise-exception:
> string is read-only: "hello"

It's not -- the existence of read-only strings is implied by 
substring/read-only, and also see:

>   (guile)Object File format
> Typically all segments of an ELF file are marked as read-only, except
> that part that represents modifiable static data or static data that
> needs load-time initialization.  Loading an ELF file is as simple as
> mmapping the thing into memory with read-only permissions, then using
> the segment table to mark a small sub-region of the file as writable.
> This writable section is typically added to the root set of the garbage
> collector as well.

I'm not aware of explicit documentation that string literals may not be 
modified (and in this case, cannot be modified). However, see the 
following mail on string mutability and program text:

https://lists.gnu.org/archive/html/guile-devel/2012-01/msg00135.html

and maybe surrounding definitions.

Greetings,
Maxime.