[slime-devel] Re: slime + defsystem

[Luke Gorrie]

This one's from comp.lang.lisp..

Artem Baguinski <artm at v2.nl> writes:

> hi
>
> if i try to load something with defsystem it'll *always* say that
> compiled files are too old or absent. it refers to correct path of
> new compiled 10 min ago files though. where should i dig?

Don't know about that part, but..

> NB: these are the questions it asks:
>
> ;    - Binary file /usr/src/lisp/McCLIM/patch.x86f is old or does not exist. 
> ;      Compile (and load) source file /usr/src/lisp/McCLIM/patch.lisp instead? 
> ;    - Should I bother you if this happens again? 
> ;    - Should I compile and load or not? 
>
> also, when i'm trying to do that in slime and defsystem asks if i
> want stuff recompiled i can't seem to be able to answer. i guess
> slime treats my pressing Return key specially and it never reaches
> the defsystem. is there a solution to this?

This is a bit tricky.

In general SLIME works with user input. When Lisp tries to read input,
a message goes to Emacs saying "I want some user input", and while
Lisp is expecting input pressing return in the REPL will do the right
thing.

The difficulty here is that defsystem wants to read with a timeout so
it is actually _polling_ for input, i.e. most of the time it is not
actually trying to read, but is waiting a while before checking if
input is available. That means that most of the time Emacs thinks Lisp
doesn't want input and so it interprets user input as a REPL
expression to be evaluated instead (since our REPL supports issuing
commands in parallel).

One solution could be to add some flow-control to the REPL and disable
request piplining. Then we would buffer up user input until Lisp tells
us whether it wants user input or the next REPL command. Maybe there's
a better way.

The workaround for now is to hack defsystem so that it does a blocking
read instead of polling. This loses the timeout feature:

  (defun mk::read-char-wait (&optional (timeout 20) input-stream
                         (eof-error-p t) eof-value)
    (declare (ignore timeout))
    (read-char input-stream eof-error-p eof-value))

-Luke