I tried coming up with an example of what you describe and was able to get output of 8 with what I show below. [This example is completely stripped down so that it only works for [1] and [- 1 ], but I believe it's equivalent logically to what you said you did.]
However, I also notice that your example's debug string in your example does not have an explicit flush with %! at the end, so that the debugging output might not be flushed to the terminal until later than you expect.
Here's what I used:
Test.mll:
{
open Ytest
open Lexing
}
rule test =
parse
"-" { MINUS }
| "1" { ONE 1 }
| "[" { LB }
| "]" { RB }
| [ ' ' '\t' '\r' '\n' ] { test lexbuf }
| eof { EOFTOKEN }
Ytest.mly:
%{
%}
%token <int> ONE
%token MINUS LB RB EOFTOKEN
%start item
%type <int> index item
%%
index:
ONE { 2 }
| MINUS ONE { Printf.printf "%n" 8; $2 }
item : LB index RB EOFTOKEN { $2 }
Parse.ml
open Test;;
open Ytest;;
open Lexing;;
let lexbuf = Lexing.from_channel stdin in
ignore (Ytest.item Test.test lexbuf)