## Safety

The keyword `UNSAFE` can precede the declaration of any interface or module to indicate that it is unsafe; that is, uses the unsafe features of the language. An interface or module not explicitly labeled `UNSAFE` is called safe.

An interface is intrinsically safe if there is no way to produce an unchecked runtime error by using the interface in a safe module. If all modules that export a safe interface are safe, the compiler guarantees the intrinsic safety of the interface. If any of the modules that export a safe interface are unsafe, it is the programmer, rather than the compiler, who makes the guarantee.

It is a static error for a safe interface to import an unsafe one or for a safe module to import or export an unsafe interface.

    Last modified on Wed Apr  3 09:38:56 PST 1996 by heydon
         modified on Mon Apr 18 14:07:05 PDT 1994 by kalsow