From: Martin DeMello <martindemello@...>
Date: 2012-11-25T17:43:26+09:00
Subject: Re: I'm exploiting Ruby references

Just as an aside, I'm not sure of the full scope of your program, but
you might find Pure interesting.

http://code.google.com/p/pure-lang/

martin

On Sat, Nov 24, 2012 at 6:47 AM, Nokan Emiro <uzleepito@gmail.com> wrote:
>
>> Smalltalk supports this with the `become` method.
>
>
> Wow!  become is a great thing.  Why don't we have a built-in become in Ruby?
> Or a general replace on every object?  The latter would be a bit more
> general,
> because swapping to objects (that's what become does if I'm right) could be
> done with three replaces.
>
>> Here's one ruby
>> implementation I found on github: https://github.com/cout/become
>
>
> Unfortunately it does not work for me.
>
> irb(main):023:0> x.become y
> irb: symbol lookup error: /...../become.so: undefined symbol: STR2CSTR
> $ _
>
>> > eq['x'][0] = eq['y']
>> >
>> >
>> > The equation system changes to this:
>> > {
>> >  "k"=>12,
>> >  "y"=>["k", :+, 1],
>> >  "a"=>"y",
>> >  "x"=>[["k", :+, 1], :*, ["a", :+, "k", :+, 1]]
>> > }
>>
>> If you're doing this sort of symbolic equation manipulation I'd
>> actually advise you to express an equation as a tree,
>
>
> It is actually a tree represented by arrays and subtrees by
> array elements in the array.
>
>>
>> and implement
>> some explicit tree rewriting code for variable substitution and
>> simplifications. It's a bit of extra work up-front, but you'll have
>> complete control of the way things are done.
>
>
> The thing is that I have to solve a huge equation system with more
> than 60 000 equations, and I'm trying to keep the memory footprint
> of the whole thing as low as possible.  The lexer already produces
> arrays in a similar format shown in my examples, and references
> make substitution "parallel" on different equations. (It's not really
> parallel, but thanks to references I can make substitutions in one
> equation, and it also happens in many other.  I don't want to build
> custom classes around it, that would just slow down things, and
> generate unnecessary metadata.
>
>>
>> values
>> (numbers or variables) are always arrays, and that an operator
>> combines two arrays to give a third array. Your use of ruby references
>> will then work happily enough -
>
>
> Yes, that is my "rescue" idea too.  It is just not very nice to have
> things in equations like [13], or what's worse [[[[13]]]], which just
> means 13.  My simplifier (which is at the moment recursive) has to
> dig through these extra layers.
>
>> one of your current problems is that
>> fixnums are immediate values, so there is no way for two variables to
>> point to the same fixnum.
>
>
> Oh, yes, you are right, but that's just because my example was wrong.
> I can deal with that.  (I can represent numbers as strings, or create a
> wrapper class around numbers to solve this.)  My main problem was
> to figure out how to replace an object with more than one references
> to it and access the new object via all the original references, even if
> the new object has a different type.  (The Fixnum 13 was an unlucky
> chice. :-)
>