Re: Designing a language in which a class can define (not just overload) operators

Vidar Hokstad <vidar@hokstad.name> wrote:
>tmk@netvision.net.il (Michael Tiomkin) wrote in message news:03-08-083...
>> > [Write your parser with generic expression rules like this:
>> >
>> > expr: expr OP5 expr /* precedence 5 operator */
>> >
>> > Then when you define a new operator at level 5, have the lexer return
>> > an OP5 for it with semantic info so the parser can figure out which
>> > operator it was. I'm pretty sure this trick was used in extensible
>> > languages before 1980. -John]
>>
>> Unfortunately, this will need 100 rules for 100 priorities.
>> [It's true. But since a language with 100 priorities would be unusable,
>> so what? -John]
>
>My solution to this problem years ago was to make the parser entirely
>dynamic. Instead of hardwiring rules to specific priorities, I defined
>almost the entire language I was working on in terms of operators with
>variable priorities. I started out with arithmetic expressions, and
>then went a little bit overboard and made everything including control
>structures expressions that were defined by:


Since nobody seems to have mentioned it - Algol 68!


You clearly have gone further but, as far as I know, Algol 68 wwas the
source of all this.


Regards,
Nick Maclaren.

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