@samoht pointed me your restartable lexer let-def/ocamllex-refill#1. There is a problem with this solution: when raising the exception, you lose the local state the lexer is into, and when you resume you restart from the initial state.

This is clearly visible when using this input seq 100000 100148 | ./restartable_lexer: on my computer, number 100146 is truncated to 146.