Condensed, yes. But also not easy on the eyes :)

Note that terse code does not always translate to good performance. Compare this code at:
https://godbolt.org/
with fx my code that uses char const* inside the FSM with a simple if / else.
The difference in assembly lines is:
370 vs >1800.
(Though this does not necessarily mean the same scaling in performance).

Watch out! You do not allocate enough space for the struct in the general case. You allocate only for the size of the pointer, which is a constant (probably 8 bytes here).