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doc: update the --verbose report format.

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* doc/bison.texinfo (Understanding): Adjust to match the
current format.
(cherry picked from commit 29e20e22e0)
This commit is contained in:
Akim Demaille
2012-03-16 10:13:16 +01:00
parent 56da1e5288
commit 84c1cdc71d
1 changed files with 138 additions and 132 deletions
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doc/bison.texinfo
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@@ -7942,14 +7942,27 @@ creates a file @file{calc.output} with contents detailed below. The
order of the output and the exact presentation might vary, but the order of the output and the exact presentation might vary, but the
interpretation is the same. interpretation is the same.
The first section includes details on conflicts that were solved thanks @noindent
to precedence and/or associativity: @cindex token, useless
@cindex useless token
@cindex nonterminal, useless
@cindex useless nonterminal
@cindex rule, useless
@cindex useless rule
The first section reports useless tokens, nonterminals and rules. Useless
nonterminals and rules are removed in order to produce a smaller parser, but
useless tokens are preserved, since they might be used by the scanner (note
the difference between ``useless'' and ``unused'' below):
@example @example
Conflict in state 8 between rule 2 and token '+' resolved as reduce. Nonterminals useless in grammar
Conflict in state 8 between rule 2 and token '-' resolved as reduce. useless
Conflict in state 8 between rule 2 and token '*' resolved as shift.
@exdent @dots{} Terminals unused in grammar
STR
Rules useless in grammar
6 useless: STR
@end example @end example
@noindent @noindent
@@ -7963,42 +7976,18 @@ State 11 conflicts: 4 shift/reduce
@end example @end example
@noindent @noindent
@cindex token, useless Then Bison reproduces the exact grammar it used:
@cindex useless token
@cindex nonterminal, useless
@cindex useless nonterminal
@cindex rule, useless
@cindex useless rule
The next section reports useless tokens, nonterminal and rules. Useless
nonterminals and rules are removed in order to produce a smaller parser,
but useless tokens are preserved, since they might be used by the
scanner (note the difference between ``useless'' and ``unused''
below):
@example
Nonterminals useless in grammar:
useless
Terminals unused in grammar:
STR
Rules useless in grammar:
#6 useless: STR;
@end example
@noindent
The next section reproduces the exact grammar that Bison used:
@example @example
Grammar Grammar
Number, Line, Rule 0 $accept: exp $end
0 5 $accept -> exp $end
1 5 exp -> exp '+' exp 1 exp: exp '+' exp
2 6 exp -> exp '-' exp 2 | exp '-' exp
3 7 exp -> exp '*' exp 3 | exp '*' exp
4 8 exp -> exp '/' exp 4 | exp '/' exp
5 9 exp -> NUM 5 | NUM
@end example @end example
@noindent @noindent
@@ -8015,14 +8004,15 @@ $end (0) 0
'/' (47) 4 '/' (47) 4
error (256) error (256)
NUM (258) 5 NUM (258) 5
STR (259)
@end group @end group
@group @group
Nonterminals, with rules where they appear Nonterminals, with rules where they appear
$accept (8) $accept (9)
on left: 0 on left: 0
exp (9) exp (10)
on left: 1 2 3 4 5, on right: 0 1 2 3 4 on left: 1 2 3 4 5, on right: 0 1 2 3 4
@end group @end group
@end example @end example
@@ -8039,11 +8029,11 @@ the location of the input cursor.
@example @example
state 0 state 0
$accept -> . exp $ (rule 0) 0 $accept: . exp $end
NUM shift, and go to state 1 NUM shift, and go to state 1
exp go to state 2 exp go to state 2
@end example @end example
This reads as follows: ``state 0 corresponds to being at the very This reads as follows: ``state 0 corresponds to being at the very
@@ -8069,27 +8059,27 @@ you want to see more detail you can invoke @command{bison} with
@example @example
state 0 state 0
$accept -> . exp $ (rule 0) 0 $accept: . exp $end
exp -> . exp '+' exp (rule 1) 1 exp: . exp '+' exp
exp -> . exp '-' exp (rule 2) 2 | . exp '-' exp
exp -> . exp '*' exp (rule 3) 3 | . exp '*' exp
exp -> . exp '/' exp (rule 4) 4 | . exp '/' exp
exp -> . NUM (rule 5) 5 | . NUM
NUM shift, and go to state 1 NUM shift, and go to state 1
exp go to state 2 exp go to state 2
@end example @end example
@noindent @noindent
In the state 1... In the state 1@dots{}
@example @example
state 1 state 1
exp -> NUM . (rule 5) 5 exp: NUM .
$default reduce using rule 5 (exp) $default reduce using rule 5 (exp)
@end example @end example
@noindent @noindent
@@ -8101,24 +8091,24 @@ jump to state 2 (@samp{exp: go to state 2}).
@example @example
state 2 state 2
$accept -> exp . $ (rule 0) 0 $accept: exp . $end
exp -> exp . '+' exp (rule 1) 1 exp: exp . '+' exp
exp -> exp . '-' exp (rule 2) 2 | exp . '-' exp
exp -> exp . '*' exp (rule 3) 3 | exp . '*' exp
exp -> exp . '/' exp (rule 4) 4 | exp . '/' exp
$ shift, and go to state 3 $end shift, and go to state 3
'+' shift, and go to state 4 '+' shift, and go to state 4
'-' shift, and go to state 5 '-' shift, and go to state 5
'*' shift, and go to state 6 '*' shift, and go to state 6
'/' shift, and go to state 7 '/' shift, and go to state 7
@end example @end example
@noindent @noindent
In state 2, the automaton can only shift a symbol. For instance, In state 2, the automaton can only shift a symbol. For instance,
because of the item @samp{exp -> exp . '+' exp}, if the lookahead is because of the item @samp{exp: exp . '+' exp}, if the lookahead is
@samp{+} it is shifted onto the parse stack, and the automaton @samp{+} it is shifted onto the parse stack, and the automaton
jumps to state 4, corresponding to the item @samp{exp -> exp '+' . exp}. jumps to state 4, corresponding to the item @samp{exp: exp '+' . exp}.
Since there is no default action, any lookahead not listed triggers a syntax Since there is no default action, any lookahead not listed triggers a syntax
error. error.
@@ -8129,14 +8119,14 @@ state}:
@example @example
state 3 state 3
$accept -> exp $ . (rule 0) 0 $accept: exp $end .
$default accept $default accept
@end example @end example
@noindent @noindent
the initial rule is completed (the start symbol and the end the initial rule is completed (the start symbol and the end-of-input were
of input were read), the parsing exits successfully. read), the parsing exits successfully.
The interpretation of states 4 to 7 is straightforward, and is left to The interpretation of states 4 to 7 is straightforward, and is left to
the reader. the reader.
@@ -8144,35 +8134,38 @@ the reader.
@example @example
state 4 state 4
exp -> exp '+' . exp (rule 1) 1 exp: exp '+' . exp
NUM shift, and go to state 1 NUM shift, and go to state 1
exp go to state 8
exp go to state 8
state 5 state 5
exp -> exp '-' . exp (rule 2) 2 exp: exp '-' . exp
NUM shift, and go to state 1 NUM shift, and go to state 1
exp go to state 9
exp go to state 9
state 6 state 6
exp -> exp '*' . exp (rule 3) 3 exp: exp '*' . exp
NUM shift, and go to state 1 NUM shift, and go to state 1
exp go to state 10
exp go to state 10
state 7 state 7
exp -> exp '/' . exp (rule 4) 4 exp: exp '/' . exp
NUM shift, and go to state 1 NUM shift, and go to state 1
exp go to state 11 exp go to state 11
@end example @end example
As was announced in beginning of the report, @samp{State 8 conflicts: As was announced in beginning of the report, @samp{State 8 conflicts:
@@ -8181,17 +8174,17 @@ As was announced in beginning of the report, @samp{State 8 conflicts:
@example @example
state 8 state 8
exp -> exp . '+' exp (rule 1) 1 exp: exp . '+' exp
exp -> exp '+' exp . (rule 1) 1 | exp '+' exp .
exp -> exp . '-' exp (rule 2) 2 | exp . '-' exp
exp -> exp . '*' exp (rule 3) 3 | exp . '*' exp
exp -> exp . '/' exp (rule 4) 4 | exp . '/' exp
'*' shift, and go to state 6 '*' shift, and go to state 6
'/' shift, and go to state 7 '/' shift, and go to state 7
'/' [reduce using rule 1 (exp)] '/' [reduce using rule 1 (exp)]
$default reduce using rule 1 (exp) $default reduce using rule 1 (exp)
@end example @end example
Indeed, there are two actions associated to the lookahead @samp{/}: Indeed, there are two actions associated to the lookahead @samp{/}:
@@ -8205,7 +8198,7 @@ NUM}, which corresponds to reducing rule 1.
Because in deterministic parsing a single decision can be made, Bison Because in deterministic parsing a single decision can be made, Bison
arbitrarily chose to disable the reduction, see @ref{Shift/Reduce, , arbitrarily chose to disable the reduction, see @ref{Shift/Reduce, ,
Shift/Reduce Conflicts}. Discarded actions are reported in between Shift/Reduce Conflicts}. Discarded actions are reported between
square brackets. square brackets.
Note that all the previous states had a single possible action: either Note that all the previous states had a single possible action: either
@@ -8224,72 +8217,85 @@ with some set of possible lookahead tokens. When run with
@example @example
state 8 state 8
exp -> exp . '+' exp (rule 1) 1 exp: exp . '+' exp
exp -> exp '+' exp . [$, '+', '-', '/'] (rule 1) 1 | exp '+' exp . [$end, '+', '-', '/']
exp -> exp . '-' exp (rule 2) 2 | exp . '-' exp
exp -> exp . '*' exp (rule 3) 3 | exp . '*' exp
exp -> exp . '/' exp (rule 4) 4 | exp . '/' exp
'*' shift, and go to state 6 '*' shift, and go to state 6
'/' shift, and go to state 7 '/' shift, and go to state 7
'/' [reduce using rule 1 (exp)] '/' [reduce using rule 1 (exp)]
$default reduce using rule 1 (exp) $default reduce using rule 1 (exp)
@end example @end example
Note however that while @samp{NUM + NUM / NUM} is ambiguous (which results in
the conflicts on @samp{/}), @samp{NUM + NUM * NUM} is not: the conflict was
solved thanks to associativity and precedence directives. If invoked with
@option{--report=solved}, Bison includes information about the solved
conflicts in the report:
@example
Conflict between rule 1 and token '+' resolved as reduce (%left '+').
Conflict between rule 1 and token '-' resolved as reduce (%left '-').
Conflict between rule 1 and token '*' resolved as shift ('+' < '*').
@end example
The remaining states are similar: The remaining states are similar:
@example @example
@group @group
state 9 state 9
exp -> exp . '+' exp (rule 1) 1 exp: exp . '+' exp
exp -> exp . '-' exp (rule 2) 2 | exp . '-' exp
exp -> exp '-' exp . (rule 2) 2 | exp '-' exp .
exp -> exp . '*' exp (rule 3) 3 | exp . '*' exp
exp -> exp . '/' exp (rule 4) 4 | exp . '/' exp
'*' shift, and go to state 6 '*' shift, and go to state 6
'/' shift, and go to state 7 '/' shift, and go to state 7
'/' [reduce using rule 2 (exp)] '/' [reduce using rule 2 (exp)]
$default reduce using rule 2 (exp) $default reduce using rule 2 (exp)
@end group @end group
@group @group
state 10 state 10
exp -> exp . '+' exp (rule 1) 1 exp: exp . '+' exp
exp -> exp . '-' exp (rule 2) 2 | exp . '-' exp
exp -> exp . '*' exp (rule 3) 3 | exp . '*' exp
exp -> exp '*' exp . (rule 3) 3 | exp '*' exp .
exp -> exp . '/' exp (rule 4) 4 | exp . '/' exp
'/' shift, and go to state 7 '/' shift, and go to state 7
'/' [reduce using rule 3 (exp)] '/' [reduce using rule 3 (exp)]
$default reduce using rule 3 (exp) $default reduce using rule 3 (exp)
@end group @end group
@group @group
state 11 state 11
exp -> exp . '+' exp (rule 1) 1 exp: exp . '+' exp
exp -> exp . '-' exp (rule 2) 2 | exp . '-' exp
exp -> exp . '*' exp (rule 3) 3 | exp . '*' exp
exp -> exp . '/' exp (rule 4) 4 | exp . '/' exp
exp -> exp '/' exp . (rule 4) 4 | exp '/' exp .
'+' shift, and go to state 4 '+' shift, and go to state 4
'-' shift, and go to state 5 '-' shift, and go to state 5
'*' shift, and go to state 6 '*' shift, and go to state 6
'/' shift, and go to state 7 '/' shift, and go to state 7
'+' [reduce using rule 4 (exp)] '+' [reduce using rule 4 (exp)]
'-' [reduce using rule 4 (exp)] '-' [reduce using rule 4 (exp)]
'*' [reduce using rule 4 (exp)] '*' [reduce using rule 4 (exp)]
'/' [reduce using rule 4 (exp)] '/' [reduce using rule 4 (exp)]
$default reduce using rule 4 (exp) $default reduce using rule 4 (exp)
@end group @end group
@end example @end example