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Postings from December 2017
On Mon, Dec 25, 2017 at 01:19:59AM -0800, KES wrote:
> # New Ticket Created by KES
> # Please include the string: [perl #132653]
> # in the subject line of all future correspondence about this issue.
> # <URL: https://rt.perl.org/Ticket/Display.html?id=132653 >
>
>
> Very often in the program there are consecutive ifs. Like this:
>
> $x = <>;
>
> if( !$x ) {
> print 1;
> }
> elsif( $x eq 'asdf' ) {
> print 2;
> }
> elsif( $x ne 'asdf' ) {
> print 3;
> }
> else {
> print 4;
> }
>
> And this is unhandy when 's' debugger command skip all ifs and do not stop on each.
> For example 'elsif' is skipped on line 8:
>
> $ perl -d ./t.pl
>
> Loading DB routines from perl5db.pl version 1.49_04
> Editor support available.
>
> Enter h or 'h h' for help, or 'man perldebug' for more help.
>
> main::(./t.pl:3): $x = <>;
> DB<1> s
> df
> main::(./t.pl:5): if( !$x ) {
> DB<1> s
> main::(./t.pl:12): print 3;
> DB<1>
>
> expected debugging:
>
> main::(./t.pl:3): $x = <>;
> DB<1> s
> df
> main::(./t.pl:5): if( !$x ) {
> DB<1> s
> main::(./t.pl:8): elsif( $x eq 'asdf' ) {
> DB<1> s
> main::(./t.pl:12): print 3;
> DB<1>
's' is documented as:
Single step. Executes until the beginning of another
statement
Perl compiles if/else chains into ?: expressions; for example,
if (C1) {
S1;
} elsif (C2) {
S2;
} elsif (C3) {
S3;
} else {
S4;
}
gets compiled to the equivalent of:
C1 ? do { S1; } : C2 ? do { S2; } : C3 ? do { S3 } : do { S4 };
which the debugger sees as a single expression.
--
More than any other time in history, mankind faces a crossroads. One path
leads to despair and utter hopelessness. The other, to total extinction.
Let us pray we have the wisdom to choose correctly.
-- Woody Allen
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