Re: Complex conditional statements

What do "if" and "undef" mean? What's the relative precedence of "unless", "or" and "if"? If your snippet is equivalent to

if (not B) {
   A 
} else {
   if (E and F) {   
      C and D
   } else {         
      undef
   }
}
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it can be written as

(not B and A)
or
(B and (
   ((E and F) and (C and D))
   or
   (not (E and F) and undef)
))
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and simplified (through logic arithmetic) to

(not B and A) or (B and E and F and C and D)
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Notes:

For convertion to single expressions:
if (A) { B } else { C } === (A and B) or (not A and C)

For simplification:
X and undef === undef
X or undef  === X
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Re^2: Complex conditional statements by bofh_of_oz (Hermit) on Jun 16, 2005 at 15:01 UTC
A great explanation, thanks a lot! It raised another question, though: if one or more of those statements (A, B etc) is a print "..." statement, how can I make it print only if B is false (as in not B and A)? UPDATE: Here's how my test code looks: `$test = $comment = 1; ($a = 3 and print "--> $a\n") if ($comment or $test) or print "no way! +\n";` [download] It works if ($comment or $test) gives true, but both print statements are executed if it gives false... -------------------------------- An idea is not responsible for the people who believe in it...	[reply] [d/l]
Re^3: Complex conditional statements by ikegami (Patriarch) on Jun 16, 2005 at 15:12 UTC
`not B and print("...")` Unlike C, every Perl function can be used in an expression, even those that don't normally return a value. But that's moot since `print` actually does return a value: true on success, false (and sets $!) otherwise. Keep in mind that using these techniques is almost guaranteed to make your code less readable or unreadable. For expressions of that magnitude, I encourage you to treat this discussion as an academic excercise. Update: Answer to Updated question: `($a = 3 and print "--> $a\n") if ($comment or $test) or print "no way!";` is the same as `($a = 3 and print "--> $a\n") if ($comment or $test or print "no way!");` Keep in mind that `print` pretty much always returns true, so the above doesn't do what you want. You could fix it by changing the return value of `print`: `($a = 3 and print "--> $a\n") if ($comment or $test) or (print("no way!"), 0);` But that's aweful code! What's wrong with `if ($comment or $test) { $a = 3; print "--> $a\n"; } else { print "no way!\n"; }` You could shorten it a little to `$comment or $test ? ( $a = 3, print "--> $a\n" ) : print "no way!\n";` but you're starting to mess with people's ability to read your code if you do that.	[reply] [d/l] [select]