From: Brian Candler <b.candler@...>
Date: 2008-10-28T06:12:38+09:00
Subject: Re: automatic code conversion from Ruby to C ?

Axel Etzold wrote:
> I am looking for a (semi-)automatic conversion of a Ruby script to C or 
> C++, so
> that readable source code for a human C/C++ programmer is produced.
> 
> The program should read in text from a file as a string, split and 
> search it using regular expressions,
> convert some numbers into floats and perform some calculations on them
> (the latter part is done using some existing C code).

It sounds like you think that you can use Ruby as a shorthand way of 
writing C. Unfortunately it doesn't work that way.

Bear in mind that the biggest pain with C is to do with memory 
allocation. Ruby has a whole run-time environment for creating and 
manipulating Ruby objects. So this mechanically-generated C code would 
just be calling Ruby libraries to create objects or dispatch methods.

So in that case, why not just write it in Ruby and run it?

The other part you say is that you want to interact with existing C 
code. This may be easier than you think. A good starting point is 
http://www.ruby-doc.org/docs/ProgrammingRuby/html/ext_ruby.html

Look also at the RubyInline gem, which lets you write C directly inside 
your Ruby (yes!)

> Is there some gem that would ...  translate it for 
> me into
> readable C/C++, such that I'd have to specify as few as possible size 
> and variable
> type declarations ?

If it did, it would just be

   VALUE foo;
   VALUE bar;
   VALUE baz;

/* VALUE is a reference to a Ruby object, whether it be an Array, a 
String, or an integer */

> and I'd have a hard time defending the use of a scripting language with 
> the people
> I am collaborating here.

Prototype it in Ruby. If it works fast enough, then you've saved 
yourself a lot of work. Even if it's too slow, you'll have a more 
concrete idea what you're trying to do and how to achieve it.

Reading 100,000 lines in Ruby doesn't take very long.

Another option would be to write a Ruby script to "normalise" your input 
into a format which is easier for your C program to read. For example, 
it could output

   point1 point2 distance

tuples. This would probably be sufficient:

src_point = nil
while line = $stdin.gets
  line.chomp!
  if line =~ /^-/
    src_point = nil
  elsif src_point.nil?
    src_point = line
  elsif line =~ /^(\S+)\s*(\d+)$/
    puts "#{src_point} #{$1} #{$2}"
  else
    STDERR.puts "Invalid line: #{line.inspect}"
  end
end

Output:

P1 P2 23
P1 P4 27
P2 P3 1
P2 P5 457
P2 P6 3
P2 P377 56

Your C program would still need to build a graph data structure from 
this though. There are probably existing C libraries to work on data 
sets like this, if you hunt hard enough.
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