[slime-devel] unexpected behavior of eval-when with CCL when compiling with C-c C-k

Helmut Eller heller at common-lisp.net
Thu Aug 30 09:23:15 UTC 2012

On Thu, Aug 30 2012, Faheem Mitha wrote:

> Hi,
> I recently posted a question at
> http://stackoverflow.com/questions/12156902/unxpected-behavior-with-eval-when
> Brief summary:
> The following code should (I think) set *read-default-float-format* to
> double float. Well, it does compile with C-c C-k, but running
> *read-default-float-format*
> in the REPL afterwards gives SINGLE-FLOAT.
> So the value of *read-default-float-format* in the REPL has not changed
> from the default value of SINGLE-FLOAT.
> Note, however, that the
> (print *read-default-float-format*)
> in the code does return DOUBLE-FLOAT.
> Rainer Joswig, in his answer to this question, says that this is
> because the compilation and the REPL are on different threads (if I
> understand him correctly), but I'd like some evidence of this.

SLIME creates a new thread for C-c C-k.  As compiling could potentially
take a long time, using a new thread seems like a reasonable thing to
do.  Therefore the code that compiles and loads your code is a different
thread than the REPL thread.

For evidence, evaluate (princ ccl:*current-process*) in the REPL and
inside the eval-when form.

> Also,
> this code works fine with SBCL.
> In addition to wanting to understand why this is happening, I'd like
> to know whether it is possible to work around this, and set
> *read-default-float-format* in a file, rather than having to set it on
> the command line.
> I'm not sure whether this issue has something to do with SLIME, so I'm
> posting here first.
> Platform and versions. I'm using Debian squeeze x86. The version of
> SLIME is from Debian unstable, 1:20120525-2. CCL is the 1.8 release. I
> tried it both with the upstream binaries from
> http://svn.clozure.com/publicsvn/openmcl/release/1.8/linuxx86/ccl, and
> a binary package created by me - see Package ccl at
> mentors.debian.net. The result was the same in each case.
> Thanks in advance. Please CC me on any reply.

When CCL creates a new thread it binds some special variables in the new
thread.  *READ-DEFAULT-FLOAT-FORMAT* is one of them.  You can see the
full list of those variables with (ccl::standard-initial-bindings).
Also look at the documentation of MAKE-PROCESS[1].  I think
CCL:DEF-STANDARD-INITIAL-BINDING can be used to change those variables
for future thread, but I know no easy way to change them in all existing


[1] http://ccl.clozure.com/ccl-documentation.html#f_make-process

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