Re^3: cross scope gotos?

[LanX]

in reply to Re^2: cross scope gotos?
in thread cross scope gotos?

Maybe this code makes it clearer:

 
sub jump { print "in\n"; goto BACK };
 
sub jump2 {goto &jump }
 
sub cont {
  for $i (0..1) {
    for $j ("a".."b") {
      print "$i,$j\t";
      jump2();          # works
      #goto &jump;      # fails
    BACK:
    }
  }
}
 
cont();

OUTPUT

0,a    in
0,b    in
1,a    in
1,b    in

in simple words:

It's not only possible to jump within the same scope, but also into the scope of previous ("outer") call frames.

(Pity I thought I found an easy pattern for continuations...)

[Anonymous Monk]

No serious application whatsoever for this nonsense...

[LanX]

> No serious application whatsoever for this nonsense...

sigh, YOU again...

you may use it for

1. easily leaving deeply nested recursions, without the need to return step by step

    perl -e '
   my $x; sub rec { goto STOP if ++$x>10; print $x; rec()};rec();STOP:' 
   12345678910
   

2. easily defining specific labels and jump-commands in DSLs (Domain Specific Languages) and encapsulating all the logic within the subs.

   For instance if you want to emulate and/or compile an assembler language you can easily implement it as valid perl-code then easily using Perl as macro language:

   use Assembler::6502;     # fictitious module 
                            # implementing Mnemonics as subs
    
   MARK:      LDX 10;
              ADD 3;
    
              macro1();     # Perl sub to include/call mnemonics 
    
              JSR SUB2;
              JMP MARK;
    
   SUB2:      ...
              ...
              RET              
   

serious enough?

UPDATE: added examples