remove internal treatment of default prompt tag, it seems there was no need

* libguile/control.h (scm_sys_default_prompt_tag):
* libguile/control.c (scm_init_control): Remove the logic that defined
  %default-prompt-tag.
  (scm_c_abort): Remove check for default prompt tag, it wasn't useful.

* libguile/throw.c (sym_pre_init_catch_tag): Define as the pre-init
  prompt tag.
  (pre_init_catch, pre_init_throw): Use sym_pre_init_catch_tag.

* module/ice-9/boot-9.scm (default-prompt-tag): Define as a simple
  value, not a fluid. Perhaps we can expose it as a fluid later.

libguile/control.c

@@ -28,8 +28,6 @@
 
 
 
-SCM scm_sys_default_prompt_tag;
-
 
 SCM
 scm_c_make_prompt (SCM k, SCM *fp, SCM *sp, scm_t_uint8 *abort_ip,
@@ -207,19 +205,9 @@ scm_c_abort (SCM vm, SCM tag, size_t n, SCM *argv, scm_t_int64 cookie)
         }
     }
   
-  /* If we didn't find anything, print a message and abort the process
+  /* If we didn't find anything, raise an error. */
-     right here.  If you don't want this, establish a catch-all around
-     any code that might throw up. */
   if (scm_is_false (prompt))
-    {
+    scm_misc_error ("abort", "abort to unknown tag", scm_list_1 (tag));
-      if (scm_is_eq (tag, scm_fluid_ref (scm_sys_default_prompt_tag)))
-        {
-          fprintf (stderr, "No prompt found for abort to default prompt tag!\n");
-          abort ();
-        }
-      else
-        scm_misc_error ("abort", "abort to unknown tag", scm_list_1 (tag));
-    }
 
   cont = reify_partial_continuation (vm, prompt, winds, cookie);
 
@@ -285,9 +273,6 @@ void
 scm_init_control (void)
 {
 #include "libguile/control.x"
-  scm_sys_default_prompt_tag = scm_make_fluid ();
-  scm_fluid_set_x (scm_sys_default_prompt_tag, scm_gensym (SCM_UNDEFINED));
-  scm_c_define ("%default-prompt-tag", scm_sys_default_prompt_tag);
 }
 
 /*

libguile/control.h

@@ -41,9 +41,6 @@ struct scm_prompt_registers
 };
 
 
-SCM_INTERNAL SCM scm_sys_default_prompt_tag;
-
-
 SCM_INTERNAL SCM scm_c_make_prompt (SCM k, SCM *fp, SCM *sp,
                                     scm_t_uint8 *abort_ip,
                                     scm_t_uint8 escape_only_p,

libguile/throw.c

@@ -498,6 +498,9 @@ scm_ithrow (SCM key, SCM args, int noreturn SCM_UNUSED)
 /* Unfortunately we have to support catch and throw before boot-9 has, um,
    booted. So here are lame versions, which will get replaced with their scheme
    equivalents. */
+
+SCM_SYMBOL (sym_pre_init_catch_tag, "%pre-init-catch-tag");
+
 static SCM
 pre_init_catch (SCM tag, SCM thunk, SCM handler, SCM pre_unwind_handler)
 {
@@ -510,7 +513,7 @@ pre_init_catch (SCM tag, SCM thunk, SCM handler, SCM pre_unwind_handler)
     abort ();
 
   vm = scm_the_vm ();
-  prompt = scm_c_make_prompt (scm_fluid_ref (scm_sys_default_prompt_tag),
+  prompt = scm_c_make_prompt (sym_pre_init_catch_tag,
                               SCM_VM_DATA (vm)->fp, SCM_VM_DATA (vm)->sp,
                               SCM_VM_DATA (vm)->ip, 1, -1, scm_i_dynwinds ());
   scm_i_set_dynwinds (scm_cons (prompt, SCM_PROMPT_DYNWINDS (prompt)));
@@ -532,7 +535,7 @@ pre_init_catch (SCM tag, SCM thunk, SCM handler, SCM pre_unwind_handler)
 static SCM
 pre_init_throw (SCM args)
 {
-  return scm_at_abort (scm_fluid_ref (scm_sys_default_prompt_tag), args);
+  return scm_at_abort (sym_pre_init_catch_tag, args);
 }
 
 void

module/ice-9/boot-9.scm

@@ -48,10 +48,13 @@
 ;; Define delimited continuation operators, and implement catch and throw in
 ;; terms of them.
 
-(define (default-prompt-tag)
-  (fluid-ref %default-prompt-tag))
 (define (make-prompt-tag . stem)
   (gensym (if (pair? stem) (car stem) "prompt")))
+(define default-prompt-tag
+  ;; not sure if we should expose this to the user as a fluid
+  (let ((%default-prompt-tag (make-prompt-tag)))
+    (lambda ()
+      %default-prompt-tag)))
 
 (define (call-with-prompt tag thunk handler)
   (@prompt tag (thunk) handler))