Re: [Boost-users] [Proto] Extracting types of sub-expression in transform

Subject: Re: [Boost-users] [Proto] Extracting types of sub-expression in transform
From: Eric Niebler (eric_at_[hidden])
Date: 2008-10-19 13:29:27

Ivan Godard wrote:
> 
> VWG was invented for and used to define Algol68. Personally, I find it 
> easiest to understand a formal system when I have a worked out example 
> in front of me. If you're the same way, I suggest starting with:
> 
>     http://en.wikipedia.org/wiki/Algol68

I don't see any discussion there of van Wijngaarden grammars, or even 
anything that is recognizable as a formal grammar. What am I supposed to 
be looking at on that page?

>     http://burks.brighton.ac.uk/burks/language/other/a68rr/rrtoc.htm
>     Lindsey, C.H. and van der Meulen, S.G., /Informal Introduction to
>     ALGOL 68/, North-Holland, 1971 (also sometimes known as "Algol68
>     without Tears")

I see a large table of contents there. Care to narrow it down for me?

> I'm biased here - I was on the working group that produced the second 
> reference above - 

Very cool.

> but I think that the only way to introduce semantics 
> into a practical and general DSEL system is via formal means. However, 
> both VWG and its exemplar in Algol68 have a very high intellectual 
> tractability barrier

Confirmed. ;-)

> , akin to the barrier facing newcomers to Functional 
> Programming or Metaprogramming. But a casual note in Boost has already 
> turned up three people who at least see the problem. That's a start :-)

I want to learn this stuff, but the references you've provided so far 
haven't helped. How badly do you want to see something like this in 
Boost? Badly enough to jump in and get your hands dirty with some code? 
Maybe you could help me to add two-level grammar support to Proto.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com