[slime-devel] Re: swank:eval-string in wrong package?

[Helmut Eller]

Peter Seibel <peter at javamonkey.com> writes:

> > You are right.  The docstring isn't quite correct.  We could probably
> > remove one level of printing/reading by passing a form instead of the
> > string.  We could then rename the function to EVAL-FOR-EMACS.
> 
> Hmmm. I'm not sure that's a good idea--I was looking at this because I
> specifically needed to evaluate a form containing symbols I grabbed
> from my emacs buffer. But I need those to be read by CL in the proper
> package. Given the emacs s-exps and CL s-exps are *not* exactly the
> same it seems better to let the communication between emacs and CL be
> via strings. Or maybe I misunderstand you.

Perhaps the issue becomes clearer with some examples.  Evaluating 
(+ 1 2) with C-x C-e proceeds as follows:

1. Emacs sends the string 
   "(:emacs-rex \"(swank:interactive-eval \\\"(+ 1 2)\\\")\" nil t 477)"
   with a 3 byte header indicating the length to Lisp.

2. Lisp reads the 3 bytes, allocates a string and copies the string
   from the socket into the string.

3. Lisp READs from the string in the swank-io-package and gets the form:
   (:emacs-rex "(swank:interactive-eval \"(+ 1 2)\")" nil t 477)

4. DISPATCH-EVENT (or READ-FROM-SOCKET-IO depending on the
   communcation style) calls EVAL-STRING with 
   "(swank:interactive-eval \"(+ 1 2)\")"

5. EVAL-STRING READs the string in the swank-io-package and calls EVAL with:
   (swank:interactive-eval "(+ 1 2)")

6. INTERACTIVE-EVAL reads the "(+ 1 2)" in the *buffer-package* and
   sends the result back to Emacs.

I think we can get rid of the READ in 5. by sending 
"(:emacs-rex (swank:interactive-eval \"(+ 1 2)\") nil t 477)"
in 1.  The :emacs-rex message is created by the slime-rex macro, and
the argument there is conceptually a form (where all symbols are
fully qualified) and not a string.  So I think we wouldn't lose 
any flexibility. 

If you need to READ in a particular package, you can use the same
approach as we do for INTERACTIVE-EVAL.

Helmut.