Re: cannot compile: srfi-10 define-reader-ctor 'hash '#,(

[Neil Jerram <neil@ossau.homelinux.net>]

On 2014-07-30 23:27, Jan Nieuwenhuizen wrote:
> Ludovic Courtès writes:
> 
> Hi,
> 
>> In this example, you want the reader extension to be available at
>> compile time, and not necessarily at run time.  However, by writing 
>> the
>> code as is, the reader extension is available only at run time, hence
>> the error.
> 
> Alright, that makes sense when you think about it...
> 
>> To require evaluation of the ‘define-reader-ctor’ form at compile 
>> time,
>> change the code to (info "(guile) Eval When"):
> 
> Wow, many thanks!  This works for me; would it be nice to have some of
> this more explicitly in the srfi-10 manual?

This same problem just came up in another thread, too (look for 
"ossaulib").  In that case the thing that needed to be enclosed in an 
'eval-when' form was adding a directory to the load path.

I wonder about possibly having some magic that would automatically match 
certain top-level forms and evaluate them at compile time.  The case for 
this for 'define-reader-ctor' feels quite strong.  For the load path 
case, it feels too hacky to try to recognize patterns like '(set! 
%load-path (append %load-path ...))', but perhaps OK if we defined an 
'add-to-load-path' procedure and applied the magic to that.

What do you think?  Would that be too magical?

Regards,
      Neil