Problem with LEFT function...

I wonder if I'm not facing to a bug in PostgreSQL.

I defined for convenience a LEFT function like this :

----------------------------------------------------------------------------
----------------------------
CREATE OR REPLACE FUNCTION LEFT( text, int) RETURNS text AS '

DECLARE
_STRori ALIAS FOR $1;
_INTlength ALIAS FOR $2;

BEGIN

RETURN SUBSTRING( _STRori, 1, _INTlength );

END'
LANGUAGE 'plpgsql';
----------------------------------------------------------------------------
----------------------------

Then I want to use this function in SQL statements.

SELECT LEFT( 'String1', 3 ) -> Str

SELECT LEFT( 'String1', 3 ) || 'End' -> StrEnd

SELECT 'Begin' || SUBSTRING( 'String1', 1, 3 ) -> BeginStr

BUT

SELECT 'Begin' || LEFT( 'String1', 3 ) -> ERROR: parser: parse error at or
near "LEFT"

Perhaps I misunderstood something but it seems there is a problem in
PostgreSQL parser.

My version is : PostgreSQL 7.2.1 on i686-pc-linux-gnu, compiled by GCC 2.96.

Patrick Fiche
email : patrick(dot)fiche(at)aqsacom(dot)com
tél : 01 69 29 36 18