Recursive evaluation of consteval functions seem even more natural than using control flow structures for traversing parameter packs.
Recursion termination is done by providing a more specialized overload of the function.

On December 4, 2023 7:24:31 p.m. EST, Frederick Virchanza Gotham via Std-Proposals <std-proposals_at_[hidden]> wrote:
>Fold expressions are fantastic and it's great what we can do with
>them. Sometimes though, some really simple operations turn into a
>really complicated fold expression involving a template lambda. That
>which could have been a very simple 'for' loop gets turned into a
>pretty elaborate fold expression, possibly with a lambda and some
>extra helper classes and helper functions to get the job done.
>
>I'm not the first person to suggest that we should have "for..." in
>the language, and so just to stir things up again, here's 3 possible
>uses of it:
>
>(1) Iterating over compile-time constants in a parameter pack
>
> #include <cstddef> // size_t
> template<std::size_t... indices>
> consteval bool contains_multiple_of_eight(std::size_t const arg)
> {
> for... ( i : indices )
> {
> if ( 0u == (i % arg) ) return true;
> }
>
> return false;
> }
>
>(2) Iterating over runtime arguments
>
> template<typename... Params>
> consteval bool contains_at_least_one_true(Params&&... args)
> {
> for... ( arg : args )
> {
> if constexpr ( requires { static_cast<bool>(arg); } )
> {
> if ( static_cast<bool>(arg) ) return true;
> }
> }
>
> return false;
> }
>
>(3) Iterating over types
>
> template<typename... Params>
> consteval bool
>all_implicitly_convert_to_false_after_default_initialisation(void)
> {
> for typename... ( P : Params )
> {
> if constexpr ( !requires { static_cast<bool>( P{} ); } )
>return false;
> }
>
> return true;
> }
>
>I'm not trying to argue here that these three examples are impossible
>to implement with normal fold expressions. I'm saying that we could
>write much more simple code if we had "for..." in the language.
>--
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