[antlr-interest] internal error

Gavin Lambert antlr at mirality.co.nz
Fri Feb 1 23:26:54 PST 2008


At 17:01 2/02/2008, Olivier Lefevre wrote:
 >
 >In fairness to me you didn't quite say that: rather, you said
 >"it's perfectly fine to bomb in this scenario", which didn't
 >give much confidence that the issue will be addressed even
 >after it becomes possible to ;-)

Actually Jim didn't say that -- I did.  And that was only half of 
what I said.

To rephrase: "It is reasonable behaviour for the parser to throw 
an exception in that case, because it is a case that it should 
never have to deal with in the first place.  This is because it is 
not an error in the input, it is an error in the code itself, and 
thus not the responsibility of that code.  (It is not possible to 
write code that can defend itself from errors in its own 
source.)  Where the defensive line should be drawn is at the 
compiler generating that code, which should detect that incorrect 
generated code will result and report it as an error to the 
grammar author.  However this is not yet possible due to the 
structure of ANTLR (since it's still using an old version 
internally), so fixing it will have to wait until the structure is 
updated."



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