Comment by jibal

Zig's sub-language and evaluation rules are exactly the same as the Zig language except that `type` is a first class type and the TypeInfo of any type can be both examined and modified. In Zig, generics are implemented by computing types--most often by a function returning a struct that is specialized to a type argument to the function.

I've been writing some D code and, while D "template" functions can take compile-time arguments that are types, they can only produce types via mixins, which are strings that are injected at the point of invocation and then parsed by the compiler. This gives you all of the power of Zig and then some, but it's not nearly as elegant (it would help a lot if D's token quote construct q{...} had lisp-like quasi-quote functionality). OTOH, I found when writing Zig it could become extremely confusing to have the comptime and runtime languages intermixed, which is often done for loop unrolling and "conditional compilation" -- whether it's a comptime or runtime operation is in many cases a function of whether the variables involved are comptime or runtime types. In D it's generally clearer because comptime operations are distinguished with such things as static if for flow control, enum for declaring comptime variables, foo!(comptime args)(runtime args) for function calls, etc.