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Postings from March 2000
Tom wrote:
> >} switch structures
>
> >Everyone wants a switch statement but nobody can agree on the right
> >way to do it.
>
> There will be something at the Perl Conference regarding this. I
> don't feel ethical pre-announcing details of unpublished work not
> my own, but perhaps the author shall, upon reading this response,
> choose to offer the group a synopsis, sample, or snapshot of his
> experiences with this.
I'm the author in question, but I'm not keen to telegraph too much
of the punch before the conference (nor do I want to have to defend
my proposal here until I have raised the unthinking masses behind me ;-)
Here's the abstract of the paper:
Where Angels Fear To Tread: A C<switch> Statement for Perl
Damian Conway
Abstract
This paper proposes a syntax and semantics for an explicit case
mechanism for Perl. The syntax is minimal, introducing only the
keywords C<switch> and C<case> and conforming to the general
pattern of existing Perl control structures. The semantics are
particularly rich, allowing any one (or more) of nearly 30 forms
of matching to be used when comparing a switch value with its
various cases. A prototype implementation of the proposed
addition is also described.
And here's an example of what you can do with the module:
%tagline = ( woohoo => 1, d'oh => 1, 'eat my shorts' => 0 );
while (<>) {
switch ($_);
case %tagline { print "homer\n"; next } # if $tagline{$_}
case /a-z/i { print "alpha\n"; next } # if $_ =~ /a-z/i
case [1..9] { print "small num\n"; next } # if 1<=$_<=9
case { $_[0] >= 10 } # if $_ >= 10
{
my $age = <>;
switch __ < $age;
case 20 { print "teens\n"; next } # if 20 < $age
case 30 { print "twenties\n"; next } # if 30 < $age
else { print "history\n"; next }
}
print "aha\n" case 42; # if $_ == 42
print "huh\n" case '?'; # if $_ eq '?'
}
The "how" and "why" I will defer until the Perl Conference.
Damian