Re: [boost] [proto] transform for flattening an expression - how?

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-18 08:59:53

On 03/17/08 23:45, Larry Evans wrote:
> On 03/17/08 17:55, Eric Niebler wrote:
>> Larry Evans wrote:
>>> Me too!  
>> I couldn't tell from your email -- what are you me too-ing?
> 
> flattening a sequence of binary operators into one list
> with a tag indicating the operator to be applied between
> elements in the list.
[snip]
And also the means for simplifying an expression somewhat
like described by Markus:

> I want to detect simultaneous occurences of
> x and -x and have them dropped from the typelist of my sum.

Use case1:

   translating a grammar expression:

      x | x

   to:

       x

Use case2:

   Step 1:
      translating grammar expression:
         A | B
      to an expression representing if it can derive empty
      string:
         empty<A> | empty<B>
      which, if A is a the epsilon symbol then emptt<A> == true_
      and the whole expression simplifies to:

          true_