perl5ever has asked for the wisdom of the Perl Monks concerning the following question:

In Perl 5.010, I'd like to write: 
my $suffix = given ($type) {
  when ("csv") { "txt" }
  when ("xml") { "xml" }
};

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I know I can effectively accomplish the same thing with a do statement and introducing a dummy lexical: 
my $suffix = do { my $result; given ($type)
  when ("csv") { $result = "txt" }
  when ("xml") { $result = "xml" }
  ... 
} $result };

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Is there another way to use given...when... in a "functional" way which avoids introducing a do statement and a dummy lexical?

Replies are listed 'Best First'.
Re: functional "given...when..."?
by BrowserUk (Patriarch) on Mar 15, 2010 at 19:43 UTC

    Making it data driven would be easier to maintain: 

    my %suffixes = ( 
    csv => 'txt', 
    xml => 'xml',
);

my $type = ...;
my $suffix = $suffixes{ $type };

    [download]
    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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[d/l]
      In general I'd like to use the full power of smart matching.
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Re: functional "given...when..."?
by almut (Canon) on Mar 15, 2010 at 20:02 UTC

    Just for kicks you could write 

    my $suffix = sub {
    given ($type) {
       when ("csv") { return "txt" }
       when ("xml") { return "xml" }
    }}->();

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    (in which case you can't use continue, of course)

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[d/l]
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Re: functional "given...when..."?
by JavaFan (Canon) on Mar 16, 2010 at 11:32 UTC
    You can of course write: 
    my $suffix = $type ~~ "csv" ? "txt"
           : $type ~~ "xml" ? "xml"
           : ....;

    [download]
    No do, no extra variable.
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[d/l]
Re: functional "given...when..."?
by JavaFan (Canon) on Mar 16, 2010 at 11:30 UTC
    Is there another way to use given...when... in a "functional" way which avoids introducing a do statement and a dummy lexical?
    No, in the same way you cannot do 
    my $r = if ($foo) then {"bar"} else {"baz"};

    [download]
    or 
    my $r = for (1, 2, 3) {$_ + 4};

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    But you can in ALGOL 68! ;-)
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[d/l]
[select]

      I guess he was hoping that given when would work line if/then: 

      print do{ if( $_ ){ 'foo' }else{ 'bar' } } for 0,1;;
bar
foo

      [download]
      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.
[reply]
[d/l]

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