Sometimes C compilers can't even agree on what counts as "correct"! With Rust, you can at least be reasonably sure that if your program compiles with your version of the compiler, it will continue to do so with all later versions, because they're coming from the same codebase and made by people who care about backward compatibility.
> Sometimes C compilers can't even agree on what counts as "correct"!
This comes primarily from the fact the C standard itself is hard to interpret right. Standard ML has less issues in this department: since the Definition is clearer and less ambiguous, implementations disagree less on what counts as correct code and what its meaning is. So having only one major language implementation isn't the only way to prevent compatibility issues.
