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Re: [PBML] Variable Interpolation

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  • Shawn Corey
    ... You should always use an argument for shift. In this case, shift works on @_ since it is inside a subroutine. Outside any subroutine, shift works on @ARGV.
    Message 1 of 20 , Jan 2, 2006
      KalyanRaj wrote:
      > as mentioned by Randal, we can put elements in a hash...
      > "shift" is a keyword in Perl which gives out first element in an array...I
      > wonder is there anyother use of "shift"
      > when i'm executing the code given by Randal, nothing is printed out....
      >
      > MailMeda --- the below code print out PBML which is what you wanted. Also
      > checkout the scope of the variables. if we place the statement
      > print $result outside reference subroutine, it wont print anything.
      >
      > my %mapping = (group => 'PBML', lang => 'perl', os => 'linux');
      > reference(group);
      > sub reference {
      > my $type = shift;
      > my $result = $mapping{$type};
      > print $result;
      > }

      You should always use an argument for shift. In this case, shift works
      on @_ since it is inside a subroutine. Outside any subroutine, shift
      works on @ARGV. To avoid confusion, always supply it with an argument.

      my $type = shift @_;


      --

      Just my 0.00000002 million dollars worth,
      --- Shawn

      "Probability is now one. Any problems that are left are your own."
      SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_

      * Perl tutorials at http://perlmonks.org/?node=Tutorials
      * A searchable perldoc is available at http://perldoc.perl.org/
    • merlyn@stonehenge.com
      ... Shawn You should always use an argument for shift. That s a bit strong. It s accepted to leave the argument off shift when it s being used in a sane way.
      Message 2 of 20 , Jan 2, 2006
        >>>>> "Shawn" == Shawn Corey <shawn.corey@...> writes:

        Shawn> You should always use an argument for shift.

        That's a bit strong. It's accepted to leave the argument off shift
        when it's being used in a sane way. I presumed the original poster
        knew what he was doing, and didn't comment on that.

        --
        Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
        <merlyn@...> <URL:http://www.stonehenge.com/merlyn/>
        Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
        See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
      • Shawn Corey
        ... Yes, it s strong but all good discipline seems strong until you reap the benefits from it. I don t think it s sane for the implied behaviour of any
        Message 3 of 20 , Jan 2, 2006
          Randal L. Schwartz wrote:
          >>>>>>"Shawn" == Shawn Corey <shawn.corey@...> writes:
          >
          >
          > Shawn> You should always use an argument for shift.
          >
          > That's a bit strong. It's accepted to leave the argument off shift
          > when it's being used in a sane way. I presumed the original poster
          > knew what he was doing, and didn't comment on that.
          >

          Yes, it's strong but all good discipline seems strong until you reap the
          benefits from it. I don't think it's sane for the implied behaviour of
          any construct to change. What it means is that when I'm reading a
          program, I have one more thing to keep track of. Anything that reduces
          this overhead is worth the effort.

          Always write your programs as though you aren't going to see them again
          for 25 years and then have to make a critical change immediately.


          --

          Just my 0.00000002 million dollars worth,
          --- Shawn

          "Probability is now one. Any problems that are left are your own."
          SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_

          * Perl tutorials at http://perlmonks.org/?node=Tutorials
          * A searchable perldoc is available at http://perldoc.perl.org/
        • KalyanRaj
          Hi, Mail Meda - the following code will give you what you want....PBML. another version of code which uses hash and return sub reference { $type = shift;
          Message 4 of 20 , Jan 2, 2006
            Hi,

            Mail Meda - the following code will give you what you want....PBML.
            another version of code which uses hash and return
            sub reference {
            $type = shift;
            %types = (
            group => "PBML",
            lang => "Perl",
            os => "Linux"
            );
            return $types{$type};
            }
            $result = reference("group");
            print "$result\n";

            Cheers,
            KalyanRaj

            -----Original Message-----
            From: perl-beginner@yahoogroups.com
            [mailto:perl-beginner@yahoogroups.com]On Behalf Of Shawn Corey
            Sent: Monday, January 02, 2006 11:28 PM
            To: perl-beginner@yahoogroups.com
            Subject: Re: [PBML] Variable Interpolation


            Randal L. Schwartz wrote:
            >>>>>>"Shawn" == Shawn Corey <shawn.corey@...> writes:
            >
            >
            > Shawn> You should always use an argument for shift.
            >
            > That's a bit strong. It's accepted to leave the argument off shift
            > when it's being used in a sane way. I presumed the original poster
            > knew what he was doing, and didn't comment on that.
            >

            Yes, it's strong but all good discipline seems strong until you reap the
            benefits from it. I don't think it's sane for the implied behaviour of
            any construct to change. What it means is that when I'm reading a
            program, I have one more thing to keep track of. Anything that reduces
            this overhead is worth the effort.

            Always write your programs as though you aren't going to see them again
            for 25 years and then have to make a critical change immediately.


            --

            Just my 0.00000002 million dollars worth,
            --- Shawn

            "Probability is now one. Any problems that are left are your own."
            SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_

            * Perl tutorials at http://perlmonks.org/?node=Tutorials
            * A searchable perldoc is available at http://perldoc.perl.org/


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          • Jenda Krynicky
            From: Shawn Corey ... I would be a bit surprised if anyone wrote: sub foo { my $bar = shift(@_); ... and would wonder why. In this
            Message 5 of 20 , Jan 3, 2006
              From: Shawn Corey <shawn.corey@...>
              > Randal L. Schwartz wrote:
              > >>>>>>"Shawn" == Shawn Corey <shawn.corey@...> writes:
              > >
              > >
              > > Shawn> You should always use an argument for shift.
              > >
              > > That's a bit strong. It's accepted to leave the argument off shift
              > > when it's being used in a sane way. I presumed the original poster
              > > knew what he was doing, and didn't comment on that.
              > >
              >
              > Yes, it's strong but all good discipline seems strong until you reap
              > the benefits from it. I don't think it's sane for the implied
              > behaviour of any construct to change. What it means is that when I'm
              > reading a program, I have one more thing to keep track of. Anything
              > that reduces this overhead is worth the effort.
              >
              > Always write your programs as though you aren't going to see them
              > again for 25 years and then have to make a critical change
              > immediately.

              I would be a bit surprised if anyone wrote:

              sub foo {
              my $bar = shift(@_);
              ...

              and would wonder why. In this case it's a generally accepted that the
              @_ gets omited. OTOH, I'd never make use of the fact that outside
              subroutines shift() means shift(@ARGV). That's something lots of
              people doesn't remember and something that might break easily if I
              tried to move the piece of code into a subroutine.

              Jenda
              ===== Jenda@... === http://Jenda.Krynicky.cz =====
              When it comes to wine, women and song, wizards are allowed
              to get drunk and croon as much as they like.
              -- Terry Pratchett in Sourcery
            • merlyn@stonehenge.com
              ... Jenda I would be a bit surprised if anyone wrote: Jenda sub foo { Jenda my $bar = shift(@_); Jenda ... Jenda and would wonder why. In this case
              Message 6 of 20 , Jan 3, 2006
                >>>>> "Jenda" == Jenda Krynicky <Jenda@...> writes:

                Jenda> I would be a bit surprised if anyone wrote:

                Jenda> sub foo {
                Jenda> my $bar = shift(@_);
                Jenda> ...

                Jenda> and would wonder why. In this case it's a generally accepted that the
                Jenda> @_ gets omited. OTOH, I'd never make use of the fact that outside
                Jenda> subroutines shift() means shift(@ARGV). That's something lots of
                Jenda> people doesn't remember and something that might break easily if I
                Jenda> tried to move the piece of code into a subroutine.

                I agree with you there. However, for a five line program:

                #!/usr/bin/perl
                my $from = shift;
                my $to = shift;
                if (-e $to) { rename $to, "$to~" or warn "cannot backup $to: $!"; }
                rename $from, $to or warn "Cannot rename $from to $to: $!";

                Will anyone really not know what "shift" is doing there? Or confuse
                it with shift(@_)?

                That's the point of defaults... they're the defaults because they're
                the most common thing you would do with that operator *in that context*.

                --
                Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
                <merlyn@...> <URL:http://www.stonehenge.com/merlyn/>
                Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
                See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
              • Shawn Corey
                ... The key phrase being in that context . My issue is that the default depends on the context. If it was the same throughout the regardless of context, I
                Message 7 of 20 , Jan 3, 2006
                  merlyn@... wrote:
                  > That's the point of defaults... they're the defaults because they're
                  > the most common thing you would do with that operator *in that context*.
                  >

                  The key phrase being "in that context". My issue is that the default
                  depends on the context. If it was the same throughout the regardless of
                  context, I wouldn't have a problem. The problem is that when I see a
                  naked shift, I have to stop and remember the context. One more thing to
                  worry about while reading a program.


                  --

                  Just my 0.00000002 million dollars worth,
                  --- Shawn

                  "Probability is now one. Any problems that are left are your own."
                  SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_

                  * Perl tutorials at http://perlmonks.org/?node=Tutorials
                  * A searchable perldoc is available at http://perldoc.perl.org/
                • merlyn@stonehenge.com
                  ... Shawn The key phrase being in that context . My issue is that the default Shawn depends on the context. If it was the same throughout the regardless of
                  Message 8 of 20 , Jan 3, 2006
                    >>>>> "Shawn" == Shawn Corey <shawn.corey@...> writes:

                    Shawn> The key phrase being "in that context". My issue is that the default
                    Shawn> depends on the context. If it was the same throughout the regardless of
                    Shawn> context, I wouldn't have a problem. The problem is that when I see a
                    Shawn> naked shift, I have to stop and remember the context. One more thing to
                    Shawn> worry about while reading a program.

                    That's why I said "10 line program". If this were a 200 line program,
                    I wouldn't bury "shift" in the middle, unless it was within 10 lines
                    of the start of a subroutine.

                    I believe it is reasonable to ask a programmer to look back about
                    ten lines to figure out the general flow of the program. I don't
                    think it's reasonable to have to maintain "state" further than that,
                    which is why I argue for 10-20 line subroutines instead of most of
                    the monoliths that I see most people write.

                    --
                    Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
                    <merlyn@...> <URL:http://www.stonehenge.com/merlyn/>
                    Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
                    See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
                  • Shawn Corey
                    ... Large monoliths have given me the willies ever since 2001: A Space Odyssey came out ;) -- Just my 0.00000002 million dollars worth, ... Probability is
                    Message 9 of 20 , Jan 3, 2006
                      Randal L. Schwartz wrote:
                      > I believe it is reasonable to ask a programmer to look back about
                      > ten lines to figure out the general flow of the program. I don't
                      > think it's reasonable to have to maintain "state" further than that,
                      > which is why I argue for 10-20 line subroutines instead of most of
                      > the monoliths that I see most people write.
                      >

                      Large monoliths have given me the willies ever since "2001: A Space
                      Odyssey" came out ;)


                      --

                      Just my 0.00000002 million dollars worth,
                      --- Shawn

                      "Probability is now one. Any problems that are left are your own."
                      SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_

                      * Perl tutorials at http://perlmonks.org/?node=Tutorials
                      * A searchable perldoc is available at http://perldoc.perl.org/
                    • mail meda
                      Hi Frnds, Thanks for your response. Bye. ... [Non-text portions of this message have been removed]
                      Message 10 of 20 , Jan 5, 2006
                        Hi Frnds,

                        Thanks for your response.

                        Bye.


                        On 1/4/06, Shawn Corey <shawn.corey@...> wrote:
                        >
                        > Randal L. Schwartz wrote:
                        > > I believe it is reasonable to ask a programmer to look back about
                        > > ten lines to figure out the general flow of the program. I don't
                        > > think it's reasonable to have to maintain "state" further than that,
                        > > which is why I argue for 10-20 line subroutines instead of most of
                        > > the monoliths that I see most people write.
                        > >
                        >
                        > Large monoliths have given me the willies ever since "2001: A Space
                        > Odyssey" came out ;)
                        >
                        >
                        > --
                        >
                        > Just my 0.00000002 million dollars worth,
                        > --- Shawn
                        >
                        > "Probability is now one. Any problems that are left are your own."
                        > SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_
                        >
                        > * Perl tutorials at http://perlmonks.org/?node=Tutorials
                        > * A searchable perldoc is available at http://perldoc.perl.org/
                        >
                        >
                        > Unsubscribing info is here:
                        > http://help.yahoo.com/help/us/groups/groups-32.html
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                        >
                        >
                        >
                        >
                        >
                        >
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                        >


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