Support for implicit tokens

[ptersilie]

In Yacc we can define implicit tokens like. From the documentation:

date  :  month_name  day  ','  year   ;

The comma , is enclosed in single quotes; this implies that the comma is to appear literally in the input.

From what I can tell, double quotes do the same thing.

[ltratt]

We've agreed that this is expected behaviour: in grmtools, the lexer is expected to lex everything, whereas Yacc does some lexing itself. We should document this in an "differences from Yacc" section.