Re: [boost] De Bruijn Bind (alternate bind syntax) Interest?

Subject: Re: [boost] De Bruijn Bind (alternate bind syntax) Interest?
From: Larry Evans (cppljevans_at_[hidden])
Date: 2010-09-04 07:09:28

On 09/03/10 10:33, David Sankel wrote:
> On Fri, Sep 3, 2010 at 8:04 AM, Stewart, Robert <Robert.Stewart_at_[hidden]>wrote:
> 
>> Larry Evans wrote:
>>> On 09/03/10 06:33, Stefan Strasser wrote:
>>>
>>> In:
>>>
>>>   lam<I>
>>>
>>> I is arity, not nesting, of the lambda expression:
>>>
>>>   http://bitbucket.org/camior/de-bruijn-bind/src#cl-45
>>>
>>> IOW:
>>>
>>>     \(x1,x2,x3).x1+x2+x3
>>> =>
>>>     lam<3>(arg<0,1>+arg<0,2>+arg<0,3>)
>>
>>    lam<3>(_0_1 + _0_2 + _0_3) (using zero-based indices)
>>
>> So much more readable, don't you think? ;-)
>>
> 
> Yes. I've added the following syntactic enhancements to the code (and
> updated README) at http://bitbucket.org/camior/de-bruijn-bind
> 
>    - abs -> lam
>    - var -> arg
>    - some _x_y shorthands for arg<x,y>()
> 

Since most of the time the user will be referring to the
arg<0,I>, why not switch args to arg to allow defaulting
the 2nd arg for the common case?  IOW, something like:

  template
  < unsigned ArgIndex
  , unsigned NestingLevel=0
  >
struct arg
;

instead of:

  template
  < unsigned NestingLevel
  , unsigned ArgIndex
  >
struct arg
;

This would allow:

  typedef arg<1> _1;
  typedef arg<2> _2;
  ...