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

I'm writing a program that I would like to have use a succint and easy to read rule format. The solution I cam up with makes -w scream bloody murder, though. Is there anything wrong with this approach? Any better ideas?

I just love to play with the ?: stuff! I tried several if{} approaches, but none were as readable. My error logs keep filling up with: "Found = in conditional, should be == at program.pl line 254." Any way to get this ignored (if it's not going to shoot me in the foot)?

Here's my sample:

$allowed{action} = 'post|edit|delete|long|short';
$query->{action} eq "post"    ? ($allowed{msgid} = '^(\d+|new)$') && (
+$allowed{data}  = '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$'):1;
$query->{action} eq "edit"    ?  $allowed{msgid} = '^(\d+|new)$':1;
$query->{action} eq "delete"  ?  $allowed{msgid} = '^(\d+)$':1;
$query->{action} eq "long"    ? ($allowed{sort}  = '^(author|date|subj
+ect|expire)$')
                             && ($allowed{msgid} = '^(\d*|all)$'):1;
$query->{action} eq "short"   ? ($allowed{sort}  = '^(author|date|subj
+ect|expire)$')
                             && ($allowed{msgid} = '^(\d+|all)$'):1;

foreach $key (keys %$query)
{   exists $allowed{$key} ? 1 : return 0;
    return 0 if $query->{$key}!~/$allowed{$key}/;
    1;
}

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BTW, I iterate over the $allowed hash to

Replies are listed 'Best First'.
RE: How to write a nice rule base?
by reptile (Monk) on Aug 30, 2000 at 02:57 UTC

    hmm... how about a suggestion on a different approach? You could put your rule base into a hash, with the 'action' possibilities as keys, storing a hashref with the 'sort' and 'msgid' etc. keys, like this (truncated) example: 

    my %RULES = (
    'post' => { 'msgid' => '^(\d+|new)$', 'data' => '...', },
    'edit' => { 'msgid' => '^(\d+|new)$', },
    ...,
};

my $allowed = $RULES{ $query->{'action'} };

foreach $key (keys %$query) {
    exists $allowed->{'key'} ? 1 : return 0;
    ...
}

    [download]

    Or, since it seems pretty obvious there can be only one action type at a time, you could probably cascade the trinary operator, like so: 

    for ($query->{'action'}) {
    $allowed = /post/    ? { ... } :
               /edit/    ? { ... } :
               /delete/  ? { ... } :
                           die "that action isn't supported";
}

    [download]

    or any variation you like there. The hash-based one is probably faster. 

    local $_ = "0A72656B636148206C72655020726568746F6E41207473754A";
while(s/..$//) { print chr(hex($&)) }

    [download]

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RE: rule base (comma operator / 'switch' construct)
by Russ (Deacon) on Aug 30, 2000 at 02:47 UTC
    The "Found = in Conditional" warning was not from the tertiary, but the logical and. Since you are not really doing a logical test, but just combining statements, I would use the comma operator, here. 
    $allowed{action} = 'post|edit|delete|long|short';
$query->{action} eq "post"
  ? (($allowed{msgid} = '^(\d+|new)$'),
    ($allowed{data}  = '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$'))
  : 1;
$query->{action} eq "edit"
  ? ($allowed{msgid} = '^(\d+|new)$')
  : 1;
$query->{action} eq "delete"
  ? ($allowed{msgid} = '^(\d+)$')
  : 1;
$query->{action} eq "long"
  ? (($allowed{sort}  = '^(author|date|subject|expire)$'),
    ($allowed{msgid} = '^(\d*|all)$'))
  : 1;
$query->{action} eq "short"
  ? (($allowed{sort}  = '^(author|date|subject|expire)$'),
    ($allowed{msgid} = '^(\d+|all)$'))
  : 1;

foreach $key (keys %$query){
  exists $allowed{$key} ? 1 : return 0;
  return 0 if $query->{$key}!~/$allowed{$key}/;
  1;
}

    [download]

    Now, that said, here's another way to handle this: 

    # Map keys to coderefs (used sort of like a switch statement)
my %ActionMap =
  (post => sub{
     $allowed{msgid} = '^(\d+|new)$';
     $allowed{data}  = '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$';
   },
   edit => sub{
     $allowed{msgid} = '^(\d+|new)$';
   },
   delete => sub{
     $allowed{msgid} = '^(\d+)$';
   },
   long => sub{
     $allowed{sort}  = '^(author|date|subject|expire)$';
     $allowed{msgid} = '^(\d*|all)$';
   },
   short => sub{
     $allowed{sort}  = '^(author|date|subject|expire)$';
     $allowed{msgid} = '^(\d+|all)$';
   });
# "Call" the coderef matching the "switch" value
$ActionMap{$query->{action}}->();

for my $key (keys %$query){
  return 0 unless exists $allowed{$key} && $query->{$key} =~ /$allowed
+{$key}/;
}

    [download]
    Notes:
    • I'm concerned about the for loop. It looks like $query->{$key} will never match /$allowed{$key}/. This was just a code example, though, so...
    • This "switch" construct avoids your void-context values. The ternary may feel easier to read, but it leaves the reader wondering what you are doing with that 1 in each ternary.
    • There are, of course, other ways to do "switch" statements...this is merely one of them.

    Russ
    Brainbench 'Most Valuable Professional' for Perl

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RE: How to write a nice rule base?
by adamsj (Hermit) on Aug 30, 2000 at 02:26 UTC
    Instead of: 
    $query->{action} eq "post" ? ($allowed{msgid} = '^(\d+|new)$') && ($al
+lowed{data}  = '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$'):1;

    [download]
    try this: 
    $query->{action} eq "post" ? %allowed = (msgid => '(^\d+|new)$' , data
+  => '^(([^|+]*[^|]+.*\|){4}[^|+]*[^|]+.*)$)', action => 'post|edit|d
+elete|long|short' ):1;

    [download]
    and so on. That works for me, though there may be a better solution. Your message was cut off before you told us why you iterate over %allowed--if you don't need the value of action in the iteration, this can be made simpler. Also, consider doing something about your use of sort as a key--the -w flag doesn't like that, either.
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