[asdf-devel] Backward incompatible improvements

[Daniel Herring]

On Sat, 29 Mar 2014, Anton Vodonosov wrote:

> 29.03.2014, 02:39, "Daniel Herring" <dherring at tentpost.com>:
>>
>> Would it be possible to have a special header in asdf files indicate that
>> the contained system(s) should be loaded using the new syntax mechanism?
>>
>> [...]
>>
>> ;; asdf:config '(asdf:+clean-readtable+)
>
> No, it's inconvenient, why use special parser if we can just directly specify
> what we want in a lisp expression.

I haven't checked recently, but in the past ASDF files have had 
significant code even before the system definition.  It was common to 
find conditionals based on *features*, comments for users to select 
from a few customization options, numbers being read, etc.

Once you have read the form, it is too late to modify the environment that 
is used to read it.  Thus I suggested that we adopt a convention to check 
for a "magic header" that changes the syntax used for the rest of the 
file.  The suggested syntax was meant to make this header invisible to 
legacy systems, unambiguous in meaning, extensible, and fairly easy to 
parse for new sysetms.

- Daniel