[jcranmer]

> For example, you can still write C code without libc because C is a language libc is just a library libcore is pretty much the same. Though Rust makes alot of assumptions that libcore _should_ be there but its possible for it not to be.

The same core/std distinction exists in C. The headers float.h, iso646.h, limits.h, stdalign.h, stdarg.h, stdbit.h, stdbool.h, stddef.h, stdint.h, stdnoreturn.h, and parts of string.h, stdlib.h, fenv.h, and math.h are required to be supported in freestanding mode.

And, frankly, just about every language has this kind of core library/standard library distinction; at some point, parts of the compiler implementation of the language need to work with the library implementation details, and vice versa. Languages like Rust and C are somewhat unusual in actually identifying a subset of the standard library that is usable without a complete implementation of the standard library.