On the other hand, type-checking the function bodies before macro expansion has other issues. For one, the declarations to which an attached macro is attached are generally not type-checked at all prior to expansion, so type-checking the body prior to expansion would be a departure from that. Additionally, type-checking a function body can be expensive at compile time, and doing that work twice (once for the function body as-written, once after expansion) could increase compile times unacceptably. Finally, type-checking the function body before macro expansion limits what can be expressed by function body macros.