load: new *load-hooks* feature.

*load-hooks* lets a .txr, .tl or .tlo file specify actions to be taken
when the loading of that file completes, whether normally or via
an exception. They are also honored by process exit.

For instance, with this, we can have a Lisp file that behaves like
a script which cleans up after itself (e.g. removing temporary files)
even if it is not run as a stand-alone program, but invoked
via (load ...). Because it's not a stand-alone program, it cannot
simply use the at-exit-call mechanism. The unwind-protect operator could
be used, but it's inconvenient because it protects a single form.
The *load-hooks* feature in effect protects all the top level forms of a
load, similarly to unwind-protect. Also, unwind-protect does not
guard against a process exit. (However, *load-hooks* does not guard
against an abnormal exit, only normal termination).

* eval.c (load_hooks_s): New symbol variable.
(run_load_hooks): New function.
(run_load_hooks_atexit): New static function.
(load): bind *load-hooks* to nil around load. Implement
the hooks processing via run_load_hooks, taking care to pass the
load-time dynamic environment that has already been undone.
(eval_init): Initialize load_hooks_s and register the *load-hooks*
variable. Register run_load_hooks_atexit with atexit, so the
current value of *load-hooks* is processed on process exit.

* eval.h (load_hooks_s, run_load_hooks): Declared.

* match.c (v_load): Similar changes as in load.

* txr.c (txr_main): Run the load hooks with run_load_hooks immediately
after processing the .txr or .tl file, before entering the listener.

* tests/019/load-hook.tl: New directory and file

* tests/load-hook.tl: New file.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.

1 files changed, 2 insertions, 1 deletions

diff --git a/eval.h b/eval.h
index 3c8fa3bc..14cd6578 100644
--- a/eval.h
+++ b/eval.h
@@ -34,7 +34,7 @@ extern val eval_error_s, if_s, call_s, identity_s;
 extern val eq_s, eql_s, equal_s, less_s;
 extern val car_s, cdr_s;
 extern val last_form_evaled;
-extern val load_path_s, load_recursive_s;
+extern val load_path_s, load_hooks_s, load_recursive_s;
 extern val special_s, struct_s;
 
 extern val dyn_env;
@@ -82,6 +82,7 @@ void trace_check(val name);
 val format_field(val string_or_list, val modifier, val filter, val eval_fun);
 val subst_vars(val forms, val env, val filter);
 val expand_quasi(val quasi_forms, val menv);
+void run_load_hooks(val load_dyn_env);
 val load(val target);
 val expand(val form, val menv);
 val expand_forms(val forms, val menv);