Maybe I should have expressed myself more clearly: The comment I replied to seemed to indicate that PHP must be bad since Facebook had a need to change it. My point was that, given the fact that Facebook has way more users than other sites and mostly serves non-cacheable pages, their needs are different than the needs of 99.9999% of other sites in the world, so the fact that they were forced to change PHP doesn't say anything about PHP's quality as a language.

Speaking as someone who works on a 2 million user enterprise app with standard PHP, i would have to counter that: 1) the footguns are easy to sidestep once you know them and are gradually getting removed, 2) standard php has traits and strict typing, but the typing is not for primitive types (which is what Hack adds) and 3) in nearly a decade i have had a single feature where i could have really used a faster php, whereas in practice my performance issues all come from the Oracle bottleneck because php is so easy to parallellize. Facebook could run on standard php, it would just require more hardware, and since releasing hhvm php has gotten a lot faster without breaking backwards compatibility.

they most probably would have made similar changes if they had used ruby or python. They have very specific problems brought on by massive scale which will expose the flaws in any scripting language.