[Xapian-tickets] [Xapian] #521: Precedence of HATE is surprising

[Xapian]

#521: Precedence of HATE is surprising
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 Reporter:  olly         |       Owner:  olly 
     Type:  defect       |      Status:  new  
 Priority:  normal       |   Milestone:  1.2.x
Component:  QueryParser  |     Version:  1.2.3
 Severity:  normal       |    Keywords:       
Blockedby:               |    Platform:  All  
 Blocking:               |  
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Comment(by dcolish):

 After looking briefly at the grammar, I think a good refactoring will be
 needed to support this style of precedence. The main issue is that the
 grammar will branch on the boolean operators before ever considering the
 hate/love operators. This means that even with precedence weight changes,
 the grammar could not support the expected output. One way to resolve this
 is to classify all binary expressions and reduce those. This way, the
 potential reduction of  '-' before 'AND' will be controlled by the
 precedence of operators. Another approach would be to structure the
 grammar to ensure the LOVE/HATE operators are reduced before the boolean
 ones; however, this could also have unintended side-effects. I did dump
 out the lemon grammar as it stands::

 // Reprint of input file "queryparser.lemony".
 // Symbols:
 //   0 $               10 HATE_AFTER_AND  20 BRA             30 stop_prob
 //   1 ERROR           11 SYNONYM         21 KET             31 stop_term
 //   2 OR              12 TERM            22 EMPTY_GROUP_OK  32
 compound_term
 //   3 XOR             13 GROUP_TERM      23 error           33 phrase
 //   4 AND             14 PHR_TERM        24 query           34
 phrased_term
 //   5 NOT             15 WILD_TERM       25 expr            35 group
 //   6 NEAR            16 PARTIAL_TERM    26 prob_expr       36 near_expr
 //   7 ADJ             17 BOOLEAN_FILTER  27 bool_arg        37 adj_expr
 //   8 LOVE            18 RANGE           28 prob
 //   9 HATE            19 QUOTE           29 term
 query ::= expr.
 query ::=.
 expr ::= prob_expr.
 expr ::= bool_arg AND bool_arg.
 expr ::= bool_arg NOT bool_arg.
 expr ::= bool_arg AND NOT bool_arg. [NOT]
 expr ::= bool_arg AND HATE_AFTER_AND bool_arg. [AND]
 expr ::= bool_arg OR bool_arg.
 expr ::= bool_arg XOR bool_arg.
 bool_arg ::= expr.
 bool_arg ::=. [ERROR]
 prob_expr ::= prob.
 prob_expr ::= term.
 prob ::= RANGE.
 prob ::= stop_prob RANGE.
 prob ::= stop_term stop_term.
 prob ::= prob stop_term.
 prob ::= LOVE term.
 prob ::= stop_prob LOVE term.
 prob ::= HATE term.
 prob ::= stop_prob HATE term.
 prob ::= HATE BOOLEAN_FILTER.
 prob ::= stop_prob HATE BOOLEAN_FILTER.
 prob ::= BOOLEAN_FILTER.
 prob ::= stop_prob BOOLEAN_FILTER.
 prob ::= LOVE BOOLEAN_FILTER.
 prob ::= stop_prob LOVE BOOLEAN_FILTER.
 stop_prob ::= prob.
 stop_prob ::= stop_term.
 stop_term ::= TERM.
 stop_term ::= compound_term.
 term ::= TERM.
 term ::= compound_term.
 compound_term ::= WILD_TERM.
 compound_term ::= PARTIAL_TERM.
 compound_term ::= QUOTE phrase QUOTE.
 compound_term ::= phrased_term.
 compound_term ::= group.
 compound_term ::= near_expr.
 compound_term ::= adj_expr.
 compound_term ::= BRA expr KET.
 compound_term ::= SYNONYM TERM.
 phrase ::= TERM.
 phrase ::= phrase TERM.
 phrased_term ::= TERM PHR_TERM.
 phrased_term ::= phrased_term PHR_TERM.
 group ::= TERM GROUP_TERM.
 group ::= group GROUP_TERM.
 group ::= group EMPTY_GROUP_OK.
 near_expr ::= TERM NEAR TERM.
 near_expr ::= near_expr NEAR TERM.
 adj_expr ::= TERM ADJ TERM.
 adj_expr ::= adj_expr ADJ TERM.

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Ticket URL: <http://trac.xapian.org/ticket/521#comment:2>
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