Perl period vs comma operator

Question

Why does

print "$str is " , ispalindrome($str) ? "" : " not" , " a palindrome\n" 

print "madam is a palindrome", but

print "$str is " . ispalindrome($str) ? "" : " not" . " a palindrome\n"

prints ""?

Answer 1

The conditional operator (? :) has higher precedence than the comma, but lower than the period. Thus, the first line is parsed as:

print("$str is " , (ispalindrome($str) ? "" : " not"), " a palindrome\n")

while the second is parsed as:

print(("$str is " . ispalindrome($str)) ? "" : (" not" . " a palindrome\n"))