There are a few differences, depending on how you evolve from the CBPV core, but basically other types may be eager or lazy. Functions can be eager (and thus st

There are a few differences, depending on how you evolve from the CBPV core, but basically other types may be eager or lazy. Functions can be eager (and thus statically know to represent an eager call tree) and sum types can be lazy (deferring choice). These distinctions are all available at the type level. To have thunking only arise from single unit-arg functions kind of depletes the logic of useful structure. But it’s not wrong to see it as an approximation.