Prior to Perl version 5.10, a  BEGIN block could also be used to initialize 'static' lexical variables in a subroutine closure. The  state variable of 5.10 implements 'static' lexicals. See Persistent Private Variables in perlsub.

Prior to 5.10:

>perl -wMstrict -le
"S();
 S();
 {
   my $s = 'hiya';
   sub S { print $s++ }
   }
 S();
"
0
1
hiya

>perl -wMstrict -le
"S();
 S();
 BEGIN {
   my $s = 'hiya';
   sub S { print $s++ }
   }
 S();
"
hiya
hiyb
hiyc
[download]

With 5.10 (the -E switch enables 5.10 features):

>perl -wMstrict -lE
"S();
 S();
 sub S { state $s = 'hiya';  print $s++ }
 S();
"
hiya
hiyb
hiyc
[download]