[Asdf-devel] syntax-control branch

Robert P. Goldman rpgoldman at sift.info
Sun Jun 1 22:25:12 UTC 2014

I haven't fully grokked the code changes in the syntax-control branch
yet.  However, I have read over the design notes in TODO, and pulled
them out into a separate file, which I am attaching here.  I have
annotated with a number of open questions, and added a bullet point to
document rationale, which is currently mostly a place-holder for a

WRT my concerns about the syntax-control modifications:

I have done some rooting around and have found a few libraries that are
intended to set up a system for interactive use with a special
readtable.  These are things like expert system shells, etc.

So at some point near the end of their system load, they will set
*READTABLE* prior to finishing the load and dropping out for the user to
deal with them.

I can see that someone might not like this -- indeed, I'd rather there
was a (START-FOO-SHELL) command instead.  On the other hand, note that
these are not really LIBRARIES; these are SYSTEMS.  These are not
intended to be slurped into something else: the programmer expects that
his/her system will load, set up things for an interactive user, and
then hand back control to the user through the REPL.

Isn't the syntax control approach fundamentally incompatible with this?

I don't think this is an especially tasty thing to do, but I'm also not
convinced that it's ASDF's job to break arbitrary CL anti-patterns.
Changing this behavior is likely to give very confusing bugs that won't
be obvious to the poor user.

On the other hand, I see files where there's something that sets the
READTABLE obviously where what's intended is to simply set the readtable
for the compiling and loading of this one file, and leaking that change
is wrong.

Note that a programmer who wants to be clean about this, in the current
world, can set the readtable at the top of a file, and restore it at the
bottom. If we take away the current behavior, the programmer who wants
to set things up for the user is just completely out of luck. Or, maybe
not: the very sophisticated ASDF user could add a PERFORM method on
LOAD-OP on the interactive system.  I think.  I haven't grokked what's
going on in syntax-control well enough.

I am in a quandary about this. IMO the problem is a hole in the CL spec,
which doesn't provide a good way to distinguish between two different
intended uses for readtables.

Before merging the syntax-control mods, I need to be convinced that it's
appropriate for the ASDF community to force a solution to this problem
on the CL community, instead of leaving the CL community to pick its way
through the issue as it has to date.

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