use of lookaheads

[Pieter Verheyden <pverheyd@vub.ac.be>]

Hi,

I wanted to use a lookahead for variables in my language. As a variable is always followed by the keyword 'in', I defined the variable token as follow:

    in = 'in';
    variable = var / 'in';

where "in" is the token for the in-keyword, and "var" is defined in the Helpers section as:

    var = letter (letter | digit )*;

With both versions, i.e. SableCC2 and SableCC3, I get the following error:

    java.lang.RuntimeException: [146,17] Look ahead not yet supported.

What does this error mean? In other words, what am I possibly doing wrong?


Thanks in advance,
Pieter.