The deterministic automata generated by ocamllex are limited to at most 32767 transitions. The message above indicates that your lexer definition is too complex and overflows this limit. This is commonly caused by lexer definitions that have separate rules for each of the alphabetic keywords of the language, as in the following example.
rule token = parse "keyword1" { KWD1 } | "keyword2" { KWD2 } | ... | "keyword100" { KWD100 } | ['A'-'Z' 'a'-'z'] ['A'-'Z' 'a'-'z' '0'-'9' '_'] * as id { IDENT id}
To keep the generated automata small, rewrite those definitions with only one general "identifier" rule, followed by a hashtable lookup to separate keywords from identifiers:
{ let keyword_table = Hashtbl.create 53 let _ = List.iter (fun (kwd, tok) -> Hashtbl.add keyword_table kwd tok) [ "keyword1", KWD1; "keyword2", KWD2; ... "keyword100", KWD100 ] } rule token = parse ['A'-'Z' 'a'-'z'] ['A'-'Z' 'a'-'z' '0'-'9' '_'] * as id { try Hashtbl.find keyword_table id with Not_found -> IDENT id }