Re: Dynamically add tokens

[Hans Aberg]

On 28 Jul 2009, at 10:02, Alex Duller wrote:

> In the language that I'm parsing it's possible to define custom  
> 'types';  I have the following two rules:
>
> type_defn:
> yTYPE yID yIS var_type ';'
>
> use_type:
> yID "=>" sig_type
>
> So, I want to somehow store whatever the user enters as yID in the  
> first rule and use it as an alias for the specified var_type when  
> yID is used in the second rule.
>
> Hope that makes sense :)

You need a lookup table which stores the grammar type. When the lexer  
reads an identifier, it checks if it has been defined, and returns its  
grammar type. If not it returns just identifier, giving the parser the  
chance to define it. So the grammar looks like this:
  definition:
    type identifier ...
  ;
Then define tokens like int_variable, double_variable, etc. This works  
also if you want to make new types: creating a variable that acts as a  
type.

  Hans