Beefy Boxes and Bandwidth Generously Provided by pair Networks
The stupid question is the question not asked
 
PerlMonks  

Re^2: cross scope gotos?

by LanX (Canon)
on Apr 06, 2010 at 15:19 UTC ( #833054=note: print w/ replies, xml ) Need Help??


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.

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

see Re^3: cross scope gotos? and goto

Cheers Rolf


Comment on Re^2: cross scope gotos?
Download Code
Re^3: cross scope gotos?
by BrowserUk (Pope) 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' } }"

    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.
      > 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

        Counter-example:

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

        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.

        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; }

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

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://833054]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others lurking in the Monastery: (4)
As of 2015-07-07 04:54 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









    Results (87 votes), past polls