use strict;
use warnings;

BEGIN {
    push @DB::typeahead,"b testsub","r";
}


sub testsub {
   warn "inside";
}


warn "outside";

testsub();
[download]

> perl -d d:/tmp/pm/db_demo.pl 

Loading DB routines from perl5db.pl version 1.57
Editor support enabled.

Enter h or 'h h' for help, or 'perldoc perldebug' for more help.

auto(-2)  DB<1> b testsub
auto(-1)  DB<2> r
outside at d:/tmp/pm/db_demo.pl line 14.
 at d:/tmp/pm/db_demo.pl line 14.
  DB<2> s
inside at d:/tmp/pm/db_demo.pl line 10.
 at d:/tmp/pm/db_demo.pl line 10.
    main::testsub() called at d:/tmp/pm/db_demo.pl line 16
  DB<2>
[download]

all it needs is more syntactic sugar to be able to read a history file.

and a wrapper module could handle the fact that

> @DB::typeahead is not a supported interface and is subject to change in the future

update

here a list of older discussions regarding typeahead, the older the better: click <Search>