[antlr-interest] Control of tab settings in ANTLR 2.7

[Wigg, J D]

Hello,
 
I am disappointed in not receiving any response to my query (Vol.36,
Issue 41, No. 9) about the use and control of tab settings in ANTLR
(2.7) which I repeat below.
 
Is this because there is a perfectly good description somewhere? If
so, I have not been able to find it by searching the ANTLR2 website
and I would be grateful if someone could tell me where it is.
 
Thank you.
 
Question 1.

I want to use a tabsize of 4 characters instead of 8 as assumed in the
constructors in CharScanner.cpp which I have changed to 4.  Is there
any other way of altering this value without altering a library
function?

Question 2.

In order to adjust column numbers correctly I have inserted an action
after detecting a tab character in the lexer of "tab()" as required
which should adjust the column number appropriately.

When there is a tab at the beginning of a line, but not elsewhere, the
column number is incorrect (too many by the tabsize) and the reason
seems to be that when the tab is at the beginning of a line the tab
function is entered twice so that the column number is advanced to 9
instead of only 5 (in my case).

I cannot see any reason for this (there appears to be only one tab at
the beginning of the line) but I can cure the problem in tab() by
first
checking if the column number is 1 then setting the new column to 2 so
that on the second entry of tab() the column number is only advanced
by tabsize once (to 5 in my case) .

Is the function working correctly and, if so, what am I doing wrong?

Thanks,

David.





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