There are a couple of gripes in the pgsql-sql list this morning about
being unable to enter CREATE RULE commands that specify multiple
actions --- those folk are getting parser: parse error at or near ""
from what appears to be perfectly valid syntax. I suppose they are
getting burnt by a broken vendor-supplied yacc. But while looking at
this, I couldn't help noticing how crufty the syntax is:
RuleActionList: NOTHING { $$ = NIL; } | SelectStmt { $$ = lcons($1, NIL); }
| RuleActionStmt { $$ = lcons($1, NIL); } | '[' RuleActionBlock ']' { $$ = $2; } |
'('RuleActionBlock ')' { $$ = $2; } ;
RuleActionBlock: RuleActionMulti { $$ = $1; } | RuleActionStmt { $$ = lcons($1, NIL); }
;
RuleActionMulti: RuleActionMulti RuleActionStmt { $$ = lappend($1, $2); } | RuleActionMulti
RuleActionStmt';' { $$ = lappend($1, $2); } | RuleActionStmt ';' { $$ = lcons($1,
NIL);} ;
RuleActionStmt: InsertStmt | UpdateStmt | DeleteStmt | NotifyStmt ;
What's wrong with that you say? Well, it allows a RuleActionBlock to
be made up of RuleActionStmts that aren't separated by semicolons.
Specifically stmt1 ; stmt2 stmt3 stmt4
has a production sequence.
I don't know if that was intentional or not, but it sure looks like
a shift/reduce conflict waiting to happen, as soon as the possible
RuleActionStmts get any more complicated. In any case, it's pretty
bizarre that a semi is only required after the first statement.
I suggest that we require separating semicolons and simplify the
RuleActionBlock production to a more conventional list style,
RuleActionBlock: RuleActionStmt | RuleActionBlock ';' RuleActionStmt | RuleActionBlock ';'
(the last alternative isn't normal list style, but it allows a trailing
semicolon which is accepted by the existing grammar).
Aside from forestalling future trouble with syntax extensions, this
might make us work a little better with old versions of yacc. I don't
know exactly why this area is a trouble spot for vendor yaccs, but it
seems to be. Simplifying the syntax may well help.
Comments? Anyone really in love with semicolon-less rule lists?
regards, tom lane
