Hello,
I was wondering what people thought about the idea of asserting the
success of the application of a production rule (fact) into the cache
(fact database) as a means of local error detection and recovery.
By local I mean in such cases where we've past a point where a failure
implies a parse error. Recovery is local and would hopefully allow the
parser to continue; however, the behavior of the parser when it
continues might be strange.
The key idea is that we want to tell the parser to continue, but that
if we simply recoded a successful application of a production rule
(i.e. matching the empty string) then there would be no indication of
a parse error, and so a marker of sorts is needed. Consider the
following simplistic example for matching nested balanced parentheses:
Expr
: '(' ExprTail
: ''
;
ExprTail
: Expr ')'
: Assert(UnmatchedParenError)
;
An assert statement is equivalent to matching the empty string with
the side-effect of adding an entry to the cache marking the successful
application of whatever is being asserted at the current input
position.
Best Regards,
Peter Goodman,
http://ioreader.com
70 Winston Circle,
Montreal, Quebec
H9S 4X6
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