Re: y.output format

[Akim Demaille]

| At 18:54 +0100 2002/01/09, Bernard Granier wrote:
| > Where can I find a  simple tutorial which explains the y.output file format 
?
| 
| It follows the standard format of bottom up parsing (Bison uses LALR(1)),
| son one can look into standard books describing that method. For example,
| Aho, Sethi & Ullman, "Compilers...".
| 
| Bison generates code for a stack machine, which uses a lookahead token to
| determine what action to take, and to find the next state. For example, in
| state 11
|     command  ->  "rule" expression_list .   (rule 7)
|     expression_list  ->  expression_list . production   (rule 10)
| 
|     "nonterminal"     shift, and go to state 12
| 
|     $default  reduce using rule 7 (command)
| 
|     production        go to state 13
| 
| the dot "." on the RHS means that this is the point the state machine has
| parsed so far, and the list below tells which action to take, and which is
| the next state after that.

$default stands `for any other lookahead', and [reduce ...] stands for
`there is another rule which wanted to be reduced here, but a
conflicting shift, or a conflicting reduce has won over this one'.  In
short, square brackets denote disabled possibilities.

If you are using 1.31 or even better, 1.49, I suggest that you had
--trace to -v: the output is then even more complete, showing the
items (i.e., the rule plus the dot) that are deducible from the
others.