why is PHP not throwing a parse error?

Question

There are lots of "Why does PHP throw an error here?" questions. Well, this is a little different. I found the following code while reworking some code written by a coworker:

foreach($arr as $key => $value) {http://google.com/
  echo $value;
  // ...
}

My first thought: "Umm...how embarrassing; he must have accidentally pasted that in there..." followed by: "Wait...there's no way this code actually runs...that should be a syntax error". And yet:

 $ php -l test.php
 No syntax errors detected

And indeed, (like so much PHP code that seemingly shouldn't run) it runs in production without trouble. So I did a little testing:

foreach($arr as $key => $value) {http://google.com/ <-- original, no error
foreach($arr as $key => $value) {http: <-- also no syntax error
foreach($arr as $key => $value) {http  <-- bingo! "Unexpected T_ECHO..."

What little tidbit of PHP's grammar is producing such strange results?

(I am using PHP 5.3.5)

Answer 1

The http: is being interpreted as a label (which are used for goto statements), and the //google.com/ as a comment (which can easily be seen through syntax highlighting).

Documentation on goto:

The goto operator can be used to jump to another section in the program. The target point is specified by a label followed by a colon, and the instruction is given as goto followed by the desired target label.