From: Logan Capaldo <logancapaldo@...>
Date: 2006-02-23T07:33:11+09:00
Subject: Re: Dynamic code generation and linking

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On Feb 22, 2006, at 4:51 PM, Benjohn Barnes wrote:

> I'm very interested in being able to dynamically generate, compile,  
> and link in c code (and potentially other languages, including  
> assembly - but c is my primary interest), from within Ruby. When I  
> say "link in", I mean have the compiled code immediately become  
> available for use by the Ruby script that asked for the compilation.
>
> So, I'm imagining something like...
>
> # Creating a parameterless c function.
> compiler.compile( 'printf( "Rock on, dudes!" );'  ).call
>
> # A c function with an integer argument.
> proc = compiler.compile( 'x' => Int, 'printf( "%d * %d = %d", x, x,  
> x*x);' )
> (1..10).each {|x| proc.call(x)}
>
> A module that encapsulated this (particularly as part of the Ruby  
> standard distribution) would allow a "pure ruby" module to have  
> native speed [1].
>
> It would also be awesome for dynamic code generation for building  
> an algorithm optimised for a very specific situation. Coming from  
> an image processing background, I find the idea quite exciting :)  
> As an example, I could be using artificial evolution to grow  
> functions that evaluate to a pretty picture. To evaluate these  
> functions at maximum speed, I could compile them down to c, and  
> execute them.
>
> Another example would be creating a parser from a BNF like  
> notation. It should be possible (making use of this module) to  
> specify a grammar with a Rubyish domain specific language, and then  
> compile that to native code and immediately make use of it from  
> within the same Ruby program.
>
> A further possibility is that it could pull all that pesky linking  
> with external libraries (well I don't get on with it anyway, but  
> it's not really my bag) in to the domain of Ruby, and make it a fun  
> thing to explore from within IRB, for example. An offshoot from  
> that would be an explorative SWIG like system: a simple c parser  
> that you can point at a library's header file, allowing you to  
> start hacking about with the c library as if you were back  
> programming BASIC on your BBC [2] :)
>
> Has anyone come across work in this direction, or is anyone working  
> on it themselves? Could anyone comment on difficulties involved, or  
> serious practical problems? I think the major issues are likely to be:
>
> 	Interfacing with the native linker.
> 	Passing stuff in and out of the c easily.
> 	Giving the c compiler header files (or bundles, or whatever it  
> needs on OS X).
>
> It's likely I'm completely missing many problems though - I'm  
> coming to this having never written a c extension for Ruby!
>
> My dream would be to encapsulate all of the platform specific nitty  
> gritty in one place, and so make it reasonably simple for anyone  
> with some c and Ruby knowledge to just dive in and start writing  
> super fast code, or linking with a library they want to play with.
>
> Sorry for a long post. I hope it will give you ideas, or stimulate  
> interest.
>
> Thank you for your time,
> 	Benjohn Barnes
>
>
> [1] Although one would want a mechanism to be able to cache  
> compiled code between runs eventually, as the compile time could  
> become annoying.
>
> [2] I think Ruby is such an enjoyable experience for me because it  
> recreates the fun, and frankly joy, I used to have with BASIC, when  
> I first learnt to program, but it allows me to concisely specify my  
> ideas in ways that I've come to need after 20 years of programming.  
> What I want to do here is get close to having BBC BASIC's build in  
> assembly :) Total expressiveness, and raw touching the metal speed  
> and control.
>

Sounds like you're looking for RubyInline:
class MyTest

   def factorial(n)
     f = 1
     n.downto(2) { |x| f *= x }
     f
   end

   inline do |builder|
     builder.c "
     long factorial_c(int max) {
       int i=max, result=1;
       while (i >= 2) { result *= i--; }
       return result;
     }"
   end
end

http://www.zenspider.com/ZSS/Products/RubyInline/
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