Re: [Boost-users] Lisp/Scheme DSEL in C++?

Subject: Re: [Boost-users] Lisp/Scheme DSEL in C++?
From: Joel de Guzman (joel_at_[hidden])
Date: 2011-11-14 23:32:50

On 11/15/2011 12:03 PM, Nathan Ridge wrote:
> 
> Hello,
> 
> I came across the following post on boost-users [1]:
> 
>>> hello all,
>>>
>>> does anybody know of an existing spirit/lisp implimentation, and is there
>>> any interest in developing such a project in open source?
>>
>> None yet, AFAIK.

There is now. There's a scheme subset implementation in
the spirit examples dir.

>> I'll be writing an example for Spirit2 to complement the tiny-C
>> virtual machine in there. What's equally interesting though is
>> that scheme (or at least a subset of it) can be implemented in
>> pure c++. No parsing, just pure DSEL in C++. Now, imagine a
>> parser that targets this DSEL (through C++) -- a source to source
>> translator. Essentially, your scheme code will be compiled into
>> highly efficient C++.
> 
> I find this quite intriguing, and I'm naturally led to ask two questions:
> 
> 1. Which subset of Scheme can be implemented in this way, with a DSEL?
> 
> 2. Has anyone actually done this?

We've done this as well. Of course you understand that this does
not really follow the lisp syntax, instead it's pure function
call syntax. What's interesting is that the DSEL generates function
objects which is interoperable with the scheme interpreter which
also generates function objects. This was the subject of our BoostCon
2010 presentation.

This scheme code:

  (define (factorial n)
    (if (<= n 0) 1
      (* n (factorial (- n 1)))))

Generates this C++ code (function objects that can be called
in both C++ and scheme):

  lambda factorial;
  factorial = if_(lte(_1, 0), 1, times(_1, factorial(minus(_1, 1))));

See libs/spirit/example/scheme

Regards,
-- 
Joel de Guzman
http://www.boostpro.com
http://boost-spirit.com