On Fri, Sep 26, 2003 at 11:04:21AM -0400, Dan Anderson wrote:
> > BEGIN blocks do not take precedence over one another--they are all
> > still executed. They are, however, executed immediately after perl
> > finishes compiling them. So, if you have the following code:
>
> Ok, so I'm guessing that the reason that 3214 is displayed is not
> because of precedence, but that every begin block is pushed into a stack
> of some kind, and when perl starts executing code, code on the top of
> the stack ends up being run first. Is that right?
>
> So it's sort of like precedence but really isn't. Which explains when
> things printed off are printed off from innermost begin to outermost
> begin, but a subroutine declared in a begin nested in other begins
> creates an error when called before the sequence in the code.
>
> Correct?
Close; it's not precedence, it's just order of execution. Much like
in math, you do multiplacation before addition--here, you do BEGIN
blocks as soon as possible, then you do "normal" code. Let me clarify
my earlier example, and maybe that will help.
1 { # (Block Outer)
2 print "A\n"; # Will be executed at runtime (since not in BEGIN block)
3 foo(); # Also a run-time execution; Not defined yet, but that's ok
4
5 BEGIN { # (Block 1)
6 print "B\n"; # Not finished compiling block yet, so not printed
7 BEGIN { # (Block 2)
8 print "C\n"; # Not finished compiling block yet, so not printed
9 sub foo { print "D\n"; }
10 }
# Finished compiling block 2, so print C
11 }
# Finished compiling block 1, so print B
12 }
RUNTIME BEGINS HERE: print A, then call foo() which prints D
Another way to say that: When perl goes to compile/execute this, it
does so in the following order (pseudocode):
____
open block Outer;
compile line 2, to be executed at runtime
compile line 3, to be executed at runtime
open block 1;
compile line 6, to be executed as soon as Block 1 finishes compilation
open block 2;
compile line 6, to be executed as soon as Block 2 finishes compilation
compile line 7, to be executed as soon as Block 1 finishes compilation
compile line 8, to be executed when called
close block 2
execute line 8 -> C
close block 1
execute line 6 -> B
BEGIN RUNTIME
execute line 2 -> A
execute line 3 (call line 'foo()' on line 9) -> D
close block Outer;
____
Does that help?
--Dks
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