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

> Basically anywhere in the current program that hasn't been optimised away:

not that easy!

perl -e'
goto INTO;
print "Start";
for $i (0..9) {
  INTO: print "STOP";
};'
Can't "goto" into the middle of a foreach loop at -e line 4.

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You can't jump to a label out of the current or previous frames!

see Re^3: cross scope gotos? and goto

Cheers Rolf

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Re^3: cross scope gotos?
by BrowserUk (Patriarch) on Apr 06, 2010 at 16:04 UTC
    You can't jump to a label out of the current or previous frames!

    I think that's (currently) an over statement: 

    perl -le"goto loop; $x=0; if( $x ){  while(1){ loop: print 'hi' } }"

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    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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      > I think that's (currently) an over statement:

      nope, while has a proper block but not a proper "frame" like foreach or subs.

      (I read somewhere that foreach has internally a frame, but no time to search now...)

      But the confusion is understandable, that's why I started the thread.

      Cheers Rolf

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        Counter-example: 

        perl -le"goto loop; $x=0; if( $x ){  for(;;){ loop: print 'hi' } }"

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        Update: Ah, you did say foreach 

        >perl -le"goto loop; $x=0; if( $x ){  for(1){ loop: print 'hi' } }"
Can't "goto" into the middle of a foreach loop at -e line 1.

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        Mind you, it's not really related to stack frames. Any required frame is created by goto. Since it's an explicit check for OP_ENTERITER, it appears more of a question of there not being any sensible way of initialising the iterator of the iterated loop into which you are jumping. 

        /* push wanted frames */

if (*enterops && enterops[1]) {
    OP * const oldop = PL_op;
    ix = enterops[1]->op_type == OP_ENTER && in_block ? 2 : 1;
    for (; enterops[ix]; ix++) {
        PL_op = enterops[ix];
        /* Eventually we may want to stack the needed arguments
         * for each op.  For now, we punt on the hard ones. */
        if (PL_op->op_type == OP_ENTERITER)
            DIE(aTHX_ "Can't \"goto\" into the middle of a foreach loo
+p");
        CALL_FPTR(PL_op->op_ppaddr)(aTHX);
    }
    PL_op = oldop;
}

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        Update: Improved phrasing of last paragraph and added supporting code.

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