On Sep27, 2011, at 10:44 , andurkar wrote: > Currently I am working on Postgresql... I need to study the gram.y and > scan.l parser files...since I want to do some qery modification. Can anyone > please help me to understand the files. What should I do ? Is there any > documentation available ?
scan.l defines the lexer, i.e. the algorithm that splits a string (containing an SQL statement) into a stream of tokens. A token is usually a single word (i.e., doesn't contain spaces but is delimited by spaces), but can also be a whole single or double-quoted string for example. The lexer is basically defined in terms of regular expressions which describe the different token types. gram.y defines the grammar (the syntactical structure) of SQL statements, using the tokens generated by the lexer as basic building blocks. The grammar is defined in BNF notation. BNF resembles regular expressions but works on the level of tokens, not characters. Also, patterns (called rules or productions in BNF) are named, and may be recursive, i.e. use themselves as sub-patters. The actual lexer is generated from scan.l by a tool called flex. You can find the manual at http://flex.sourceforge.net/manual/ The actual parser is generated from gram.y by a tool called bison. You can find the manual at http://www.gnu.org/s/bison/. Beware, though, that you'll have a rather steep learning curve ahead of you if you've never used flex or bison before. best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
