[antlr-interest] Interesting Problem

[Hensley, Richard]

I have an interesting parsing problem. I want dig certain context free
constructs out of a file, while ignoring all the other constructs in the
file. My specific case is that I have a file with a bunch of SQL in it,
but all I really care about are the create table statements. The create
table statements I'm concerned with can be parsed with the following
rules:

createTable 
    :   "create" (ID)* "table" ID LPAREN columns RPAREN 
    ; 
    
columns 
    :   column (COMMA column)* 
    ; 
    
column 
    :   name datatype (ID)* 
    ; 
    
datatype 
    :   (   "varchar" (size)* 
        |   "varchar2" (size)* 
        |   "number" (size)* 
        |   "date" 
        |   "integer" 
        |   "long" ("raw")* 
        ) 
    ; 
    
size 
    :   LPAREN CARDINAL RPAREN 
    ; 

To solve this problem, I'm thinking of using token stream filters, but I
can't look ahead in a token stream filter so that I could recognize when
I'm in a create table statement.

My basic design would be to use a filter that turns on output of tokens
when in a create table statement, and the parser grammar would have a
semantic rule that would turn off token output when the create table
statement has been fully recognized.

Does anybody have any experience with such a thing? 

Richard Hensley 

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