Crystals, as it allows you to specify zero types in your entire project should you want to, whilst still type checking in a language where every type is implicitly a union (eg. "this is a string or an int or null").

The result of that is a cyclical graph where nodes are traversed several times over per pass, for several passes, with increasingly more information until it reaches a state where all callers have been accounted for.

Julia allows you to specify no types, and it still supports incremental compilation.

Wow.

Thanks for both of your replies.

The last paragraph of your reply above reminds me somewhat of a part of this talk, somewhere near the end:

Lang NEXT 2014 Panel Systems Programming in 2014 and Beyond

https://youtu.be/ZQR32nTVF_4?si=zQNTWBXcp4TkSnRh

It is the part where Bjarne Stroustrup talks about the issue of the huge compilation times of multi-file C++ projects, due to the number of times that header files are repeatedly included, IIRC. The section is a bit funny, with the responses from the other participants.

There may be a solution for by now (modules), but I am not a C++ guy, so don't know if it exists or is good enough.

Interested to know what others think of this.