Re: OT(slightly): parser generator for expression with custom operators

[Lorenzo Donati <lorenzodonatibz@...>]

On 29/06/2011 18.09, steve donovan wrote:
> On Wed, Jun 29, 2011 at 5:48 PM, Lorenzo Donati
> <lorenzodonatibz@interfree.it>  wrote:
> > For example, consider math vectors:
> >
> > W = V1 :x: V2 + V3
> > W = V1:cross_product(V2) + V3   -- less readable
>
> OK, good one. But you could overload ^ for that, and * for dot
> product. (And % is also available)

Oh yes. I did it sometimes.

> True, :x: is cute. To answer your question, one thing that LuaMacro
> can not do is parse infix expressions. You could define ':x:' as a
> lexical token and replace it by '%', that kind of thing.  But for such
> a simple step, gsub is your friend ;)

Yes. I also read the stuff about "pseudo-custom" operators in the WIKI 
with all those tricks with higher order functions to capture arguments 
and the like.

I use those tricks sometimes, but to tame the syntax of a DSL, but not 
for custom operators, since they are too ugly anyway.

With gsub the problem begin when mixing prefix/postfix/infix operators 
and when the expression gets complex (just where a custom math-dsl 
should help!), so I never pushed it too far.

> steve d.

-- Lorenzo