In D which has CTFE support since ages, you'd debug such functions by invoking them at runtime. https://tour.dlang.org/tour/en/gems/compile-time-function-evalua

In D which has CTFE support since ages, you'd debug such functions by invoking them at runtime. https://tour.dlang.org/tour/en/gems/compile-time-function-evaluation-ctfe https://tour.dlang.org/tour/en/gems/compile-time-function-ev... There are also tools to print values at compile time. A compile time debugger for the CTFE interpreter is on our extended feature list for the current interpreter rewrite, but it's less of a priority atm.