C is very safe if you are experienced and don't do anything fancy. What else would you use apart from Ada? I wouldn't trust any language with a large runtime

C is very safe if you are experienced and don't do anything fancy. What else would you use apart from Ada? I wouldn't trust any language with a large runtime like Python, Java, and yes, also not Haskell. C is very amenable to proofs that use Knuth's proof style. Also of course Frama C exists. EDIT: If Rust is more mature, it may be an option, but I'd wait at least 5 more years until (if?) it is widely used.