############
# SPY_SUBS #
############

sub spy_subs {
  my ( $pack , $callback ) = @_ ;
  $pack =~ s/::$// ;
  
  my $stash = *{"$pack\::"}{HASH} ;
  
  foreach my $Key ( keys %$stash ) {
    my $sub = "$pack\::$Key" ;
    if ( defined &$sub ) {
      my $org_sub = \&$sub ;
      *{$sub} = sub { &$callback(@_) ; &$org_sub(@_) ;} ;
    }
  }
}

###############
# PACKAGE FOO #
###############

package foo ;

  sub call {
    print "call>> @_\n" ;
  }
  
  sub foo {
    print "foo>> @_\n" ;
  }
  
  main::spy_subs('foo',\&call) ;
  
  foo(123);