Date: Wed, 24 Sep 1997 10:45:53 -0400
From: Binoy Samuel <binoy@ccs.neu.edu>
To: Karl Lieberherr <lieber@ccs.neu.edu>
CC: binoy@ccs.neu.edu
Subject: Lookahead ll(k) usage

** *lookahead* keyword

Parser lookahead directives can be specified at choice points in the
class dictionary grammar with "*lookahead* (@ <directive> @)".  A
choice point is one of:

    * An alternation:  		Foo : *lookahead* (@ 2 @) Bar 
				    | Baz.
    // lookahead 2 applies only to Bar
    * An optional part:		Foo = [ *lookahead* (@ 2 @) Bar ].
    * A repetition part:	Foo ~ { *lookahead* (@ 2 @) Bar }.

A lookahead directive is one of:

    * An integer: the number of tokens to look ahead. (default is 1)
    * A parser rule or set of rules: each class Foo has a rule _Foo();
	a lookahead directive (@ _Foo() _Bar() @) means to look ahead
	until Foo and Bar have been matched.
    * A lookahead directive (@ ("x" | "y") "z" @) means to lookahead 
	until you find token 'x' followed by 'z' or 'y' followed by 'z'.
    * An arbitrary boolean Java expression, inside curly brackets. 

See the file examples/Lookahead/README in the JavaCC distribution for
more detail on how this works and when it is needed.

-------
We recommend that you make your class dictionaries LL(1)
(use no lookahead rules) if the language is under your control.
The language will be easier to learn and read.