[antlr-interest] RFC re/ Left factoring and Syntactic Predicate

[Subhobroto Sinha]

The FLOAT vs INT issue is an often repeated topic, and as I am currently in the same trap, I wish to resolve it as much as possible (to benefit me as well as others)

Intutively defn. of an INT is : ('0' .. '9')+;
A FLOAT is : : INT '.' INT;

Let's write that again :

coefficient : INT | INT DOT INT;

Left Factoring :

coefficient : INT leftNumFactor;

leftNumFactor : DOT INT | /* epsilon */;

However, ANTLR barks at me in a rule in my TreeWalker :

csvCoeffs : (coefficient)+;

It says :

DSD.mail.g:40: warning:nondeterminism upon
DSD.mail.g:40:     k==1:INT
DSD.mail.g:40:     between alt 1 and exit branch of block

I am really in the dark here. I am sure I left factored right, so where is the problem ?
I might mention that the program is working just as I wanted, but I feel bad about any warnings ;)

The complete grammar is available at http://www.geocities.com/subhobrotosinha/dsdmail.txt
The version employing syntactic predicate is at http://www.geocities.com/subhobrotosinha/dsd.txt

On the other hand, an alternate version of mine, which employs syntactic predicate on FLOAT and INT seems to work too, but issues similar nondeterminism warnings in the TreeWalker ?

What am I doing wrong in the tree walker ?

Also, what are your views on left factoring vs. syntactic predicates ?

Regards

Subhobroto Sinha
http://www.geocities.com/subhobrotosinha
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