Yesterday I wrote the following "opinion":

| print gets its "arguments in reverse order", similar to C.
| The above call would (in C) look like
|(pseudocode): 
| ...
| XPUSH( "\n" );
| XPUSH( $| );
| $|--;               # plus true/false magic
| XPUSH( "second=" );
| XPUSH( $| );
| XPUSH( "first=" );
| PUTBACK;
| call_pv("print", G_ARRAY);
| ...
| (please correct here me if I'm wrong)

which turned out to be completely wrong.
After reading the other posts and looking further
into the topic, I came to the conclusion that perl
evaluates the argument list before calling into a sub-
routine always left-to-right.

This can be shown by reading the deparsed output
from B::Bblock /1/. If used on the following lines: 
1:     $| = 1;
2:     print "first=", $|, " second=", $|--, "\n";

[download]
the important output will be: 
  OP (0x824de58) enter
  COP (0x81f3290) nextstate
#1   $| = 1
  SVOP (0x824dc80) const [6] IV (0x8167cdc) 1
  PADOP (0x818ae48) gvsv  GV (0x8168894) *|
  BINOP (0x8189398) sassign
#
  COP (0x824c638) nextstate
  OP (0x8250178) pushmark
# 2
  SVOP (0x8189428) const [7] PV (0x816881c) "first="
  PADOP (0x818c6f0) gvsv  GV (0x8168894) *|
  SVOP (0x818de00) const [8] PV (0x8168828) " second="
  PADOP (0x824ff88) gvsv  GV (0x8168894) *|
  UNOP (0x824fe50) postdec [4]
  SVOP (0x824de38) const [9] PV (0x81688b8) "\n"
  LISTOP (0x8250150) print
#
  LISTOP (0x824dac0) leave [1]

[download]
from where it can be learned that the $| decrement
occurs (postdec [4]) where it should.

Sorry for writing such a mess without checking before :-(

Regards

mwa

/1/ perl -MO=Bblock mysource.pl

In reply to Re: Puzzling $| behavior by mwah
in thread Puzzling $| behavior by saintmike

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