perl4 to perl5.004 converion with debugger problem

jmm@elegant.com (John Macdonald) wrote
> The other issue is an annoyance rather than a stopper.  As cited
> in perl425traps, "stuff${'var}more stuff" is no longer
> supported, only $::var and ${::var} are recognized with a
> string.  Changing the ' to :: means that the code is no longer
> perl4 compatible.  I don't want to have ongoing work on two
> versions (perl4 and perl5), so the only good workaround, for
> now, is to break the string into:
>
>     "stuff" . $'var . "more stuff"
>
> As I said, it's an annoyance - there's lots of them in the code
> and a significant proportion of the conversions to . would cause
> lines that ought to be wrapped for readability purposes.
>
> Is there any hope of getting the $' syntax recognized within
> strings?  (Sigh, I'm sure it's too late for it to go into
> 5.004_01, though.)

I think it would be a very bad idea to retrofit this.    Having single
quotes which don't start quoted strings is a syntactic ambiguity
nightmare.    Consider soft references such as "stuff${'var'}more stuff".
(I presume that's why it had to be removed.)

You can avoid this problem, and not extend the lines quite as much, by
explicitly including the package name:

     "stuff${main'var}more stuff"

which works compatibly in perl4 and perl5.

Attached is a suggested patch for perltrap.

p5p-msgid: E0wdKJY-00010w-00@taurus.cus.cam.ac.uk

diff --git a/pod/perltrap.pod b/pod/perltrap.pod
index 7ba57d0..9382789 100644 (file)
--- a/pod/perltrap.pod
+++ b/pod/perltrap.pod
@@ -438,6 +438,12 @@ whether this should be classed as a bug or not.
     # perl4 prints: x=10
     # perl5 prints: Can't find string terminator "'" anywhere before EOF
 
+You can avoid this problem, and remain compatible with perl4, if you
+always explicitly include the package name:
+
+    $x = 10 ;
+    print "x=${main'x}\n" ;
+
 Also see precedence traps, for parsing C<$:>.
 
 =item * BugFix