problems with parser

Massimo Dal Zotto ha scritto:

Hi,

I have some problems with the parser.

1) Of the following queries, submitted with libpgtcl, the first two are
parsed correctly while the third gives a parse error:

1. select 1
2. select 1; select 2;
3. select 1; select 2
ERROR: parser: parse error at or near ""

It seems that when a query consiste of two or more statements the
last one must be terminated by ';'. In my opinion this is not
correct because it is not consistent with case 1) and because it
breaks many existing programs compatible with previous versions
of pgsql where the syntax of point 2) was considered valid.

The same problem applies also to the body of sql functions, while it
doesn't apply to query submitted by psql because they are splitted
in separate statements submitted one by one.

2) The following query does't work:

create operator *= (
leftarg=_varchar,
rightarg=varchar,
procedure=array_varchareq);
ERROR: parser: parse error at or near "varchar"

The query should work because it is consistent with the documented
syntax of the create operator:

Command: create operator
Description: create a user-defined operator
Syntax:
CREATE OPERATOR operator_name (
[LEFTARG = type1][,RIGHTARG = type2]
,PROCEDURE = func_name,
[,COMMUTATOR = com_op][,NEGATOR = neg_op]
[,RESTRICT = res_proc][,JOIN = join_proc][,HASHES]
[,SORT1 = left_sort_op][,SORT2 = right_sort_op]);

and varchar is a valid type name (it is in pg_type).
After a litte experimenting it turned out that varchar is also a
reserved word and therefore not acceptable as a type name. To have
the above statement work you must quote the word "varchar".

Yes but some times the parser understands the keyword varchar without "" as in:

create function "varchar"(float) returns varchar as
^^^^^^ ^^^^^^
'begin
return $1;
end;
' language 'plpgsql';
CREATE

drop table a;
DROP
create table a (a float8);
CREATE
insert into a values (1.2);
INSERT 128074 1

or in the CAST()...

select cast(a as varchar) from a;
varchar
-------
1.2
(1 row)

select varchar(a) from a;
ERROR: parser: parse error at or near "a"
select "varchar"(a) from a;
varchar
-------
1.2
(1 row)

This is somewhat inconsistent with the syntax of create operator
and may confuse the user.

3) The above query introduces another problem. How can the user know
what is wrong in the input. In the example "parse error at or near"
is not a very explicative message. If I had read "reserved keyword"
instead I would not have spent time trying to figure out what's
wrong in my query.

The parser should be made more verbose and helpful about errors.

4) And another related question: if the casual user can be confused
by obscure parser messages how can the postgres hacker debug the
parser grammar? I tried with gdb but it is completely useless given
the way the parser work.
Is there any tool or trick to debug the grammar?

--
Massimo Dal Zotto

+----------------------------------------------------------------------+
|  Massimo Dal Zotto               email: dz@cs.unitn.it               |
|  Via Marconi, 141                phone: ++39-0461534251              |
|  38057 Pergine Valsugana (TN)      www: http://www.cs.unitn.it/~dz/  |
|  Italy                             pgp: finger dz@tango.cs.unitn.it  |
+----------------------------------------------------------------------

PostgreSQL 6.5.0 on i586-pc-linux-gnu, compiled by gcc 2.7.2.3
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Jose'

[Charset ISO-8859-1 unsupported, filtering to ASCII...]

Hi,

I have some problems with the parser.

1) Of the following queries, submitted with libpgtcl, the first two are
parsed correctly while the third gives a parse error:

1. select 1
2. select 1; select 2;
3. select 1; select 2
ERROR: parser: parse error at or near ""

It seems that when a query consiste of two or more statements the
last one must be terminated by ';'. In my opinion this is not
correct because it is not consistent with case 1) and because it
breaks many existing programs compatible with previous versions
of pgsql where the syntax of point 2) was considered valid.

The same problem applies also to the body of sql functions, while it
doesn't apply to query submitted by psql because they are splitted
in separate statements submitted one by one.

Added to TODO list.

2) The following query does't work:

create operator *= (
leftarg=_varchar,
rightarg=varchar,
procedure=array_varchareq);
ERROR: parser: parse error at or near "varchar"

The query should work because it is consistent with the documented
syntax of the create operator:

Command: create operator
Description: create a user-defined operator
Syntax:
CREATE OPERATOR operator_name (
[LEFTARG = type1][,RIGHTARG = type2]
,PROCEDURE = func_name,
[,COMMUTATOR = com_op][,NEGATOR = neg_op]
[,RESTRICT = res_proc][,JOIN = join_proc][,HASHES]
[,SORT1 = left_sort_op][,SORT2 = right_sort_op]);

and varchar is a valid type name (it is in pg_type).
After a litte experimenting it turned out that varchar is also a
reserved word and therefore not acceptable as a type name. To have
the above statement work you must quote the word "varchar".

This is somewhat inconsistent with the syntax of create operator
and may confuse the user.

Also added to TODO list.

3) The above query introduces another problem. How can the user know
what is wrong in the input. In the example "parse error at or near"
is not a very explicative message. If I had read "reserved keyword"
instead I would not have spent time trying to figure out what's
wrong in my query.

The parser should be made more verbose and helpful about errors.

4) And another related question: if the casual user can be confused
by obscure parser messages how can the postgres hacker debug the
parser grammar? I tried with gdb but it is completely useless given
the way the parser work.
Is there any tool or trick to debug the grammar?

I have not looked at this particular problem, but usually the errror
generated by the parser are poor. Unfortunately, I don't know of any
way to insert our own error messaged based on the type of parser
failure. This is locked up in yacc/bison.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist@candle.pha.pa.us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

I have some problems with the parser.
1) Of the following queries, submitted with libpgtcl,

Massimo, what version of Postgres are you running? Is this a new
problem in the v6.5 beta (which includes a few changes from Stefan
which might have adversely affected the behavior)?

- Tom

--
Thomas Lockhart lockhart@alumni.caltech.edu
South Pasadena, California

I have some problems with the parser.
1) Of the following queries, submitted with libpgtcl,

Massimo, what version of Postgres are you running? Is this a new
problem in the v6.5 beta (which includes a few changes from Stefan
which might have adversely affected the behavior)?

It was a snapshot of 10-15 days ago. I have seen the problem also in
previous snapshots. The problem is in the grammar in the definition
of multiple queries but unfortunately I don't know yacc enough to fix
the bug.

--
Massimo Dal Zotto

+----------------------------------------------------------------------+
|  Massimo Dal Zotto               email: dz@cs.unitn.it               |
|  Via Marconi, 141                phone: ++39-0461534251              |
|  38057 Pergine Valsugana (TN)      www: http://www.cs.unitn.it/~dz/  |
|  Italy                             pgp: finger dz@tango.cs.unitn.it  |
+----------------------------------------------------------------------+

[Charset ISO-8859-1 unsupported, filtering to ASCII...]

I have some problems with the parser.
1) Of the following queries, submitted with libpgtcl,

Massimo, what version of Postgres are you running? Is this a new
problem in the v6.5 beta (which includes a few changes from Stefan
which might have adversely affected the behavior)?

It was a snapshot of 10-15 days ago. I have seen the problem also in
previous snapshots. The problem is in the grammar in the definition
of multiple queries but unfortunately I don't know yacc enough to fix
the bug.

The bug still exists. Just start 'postgres' manually without the
postmaster, and type in a query:

#$ aspg gdb /u/pg/bin/postgres
GNU gdb
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you
are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for
details.
This GDB was configured as "i386-unknown-bsdi4.0"...run -
(gdb) run -D /u/pg/data test
Starting program: /u/pg/bin/postgres -D /u/pg/data test

POSTGRES backend interactive interface
$Revision: 1.111 $ $Date: 1999/05/09 23:31:47 $

select 1; select 2

ERROR: parser: parse error at or near ""
ERROR: parser: parse error at or near ""

select 1;select 2;

blank
1: ?column? (typeid = 23, len = 4, typmod = -1, byval = t)
----
1: ?column? = "1" (typeid = 23, len = 4, typmod = -1, byval = t)
----
blank
1: ?column? (typeid = 23, len = 4, typmod = -1, byval = t)
----
1: ?column? = "2" (typeid = 23, len = 4, typmod = -1, byval = t)
----

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist@candle.pha.pa.us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026