print is not a function中文EN

This comes from a seemingly bizarre problem:

if (print("1\n") && print("2\n") && print("3\n") && print("4\n")) {
    ;
}

What do you expect this code to output?
The actual output is:

4
111

Often we overlook the fact that print is a language construct, not a function. Its argument list doesn't require parentheses (even if you write them, the parentheses are ignored during parsing). It's simply an "expression" that always returns 1:

expr :
   T_PRINT expr
 | '(' expr ')'
;

So in PHP's view, the code above is really:

if (print ("1\n" && print ("2\n" && print ("3\n" && print "4\n")))) {
  ;
}

That is, it outputs 4, then outputs "3\n" && the result of print which is 1, then outputs "2\n" && 1, and finally "1\n" && 1.
If we actually want to achieve the original intent of the code above, we should write it like this:

if ((print "1\n") && (print "2\n") && (print "3\n") && (print "4\n")) {
    ;
}