faster (make-prompt-tag); default-prompt-tag is a parameter

* module/ice-9/boot-9.scm (default-prompt-tag): Once parameters have
  booted, redefine as a parameter.
  (make-prompt-tag): Change from a gensym to a list.  Thanks to Mark
  Weaver for the suggestion.

* doc/ref/api-control.texi (Prompt Primitives): Update docs.

1 files changed, 6 insertions, 3 deletions

diff --git a/doc/ref/api-control.texi b/doc/ref/api-control.texi
index ca7ad4af6..6eac8726f 100644
--- a/doc/ref/api-control.texi
+++ b/doc/ref/api-control.texi
@@ -494,14 +494,17 @@ those passed to @code{abort-to-prompt}.
 @end deffn
 
 @deffn {Scheme Procedure} make-prompt-tag [stem]
-Make a new prompt tag.  Currently prompt tags are generated symbols.
-This may change in some future Guile version.
+Make a new prompt tag.  A prompt tag is simply a unique object.
+Currently, a prompt tag is a fresh pair.  This may change in some future
+Guile version.
 @end deffn
 
 @deffn {Scheme Procedure} default-prompt-tag
 Return the default prompt tag.  Having a distinguished default prompt
 tag allows some useful prompt and abort idioms, discussed in the next
-section.
+section.  Note that @code{default-prompt-tag} is actually a parameter,
+and so may be dynamically rebound using @code{parameterize}.
+@xref{Parameters}.
 @end deffn
 
 @deffn {Scheme Procedure} abort-to-prompt tag val1 val2 @dots{}