Re: Patch for HalfOrder, help please!

On 11/26/06, Nobuyoshi Nakada <[e-mail]> wrote:
>
> Hi,




<cut>
> lib/tsort.rb may help you?


No but  I have to appologize for the confusion.

> [2 halforder.patch.tar.bz2 <application/x-bzip2 (base64)>]
>
> It was empty.


Sorry about that, I will try to be less confused this time

--
> Nobu Nakada
>
> I have patched my ruby with a HalfOrder module thaught as an optional
replacement of the  #== paradigm.

<explanation of my motivation>
Halforder relies on the definition of <= to define all other comparision
operators.
Note that if for all a,b in a class  a <=b || b <=a holds we have the normal
order, only that we can implement domains where a <= b || b <=a is not true
for all a,b.
This cannot be done with <=> where a<=>b has to return x from {-1,0,1}.
Performance is not a concern.
</explanation>

As this seemed to be a very easy task for someone who never has looked at
the ruby code before off I went :)
<code>
VALUE rb_mHalfOrder;
static ID less_than;
...
static VALUE
ho_gt(x, y)
    VALUE x, y;
{
    VALUE c;

    if (x == y) return Qfalse;

    // y <= x ?
    c = rb_funcall(y, less_than, 1, x);

    if (NIL_P(c)) return Qfalse;
    if ( c == Qfalse ) return c;

    // x <= y ?
    c = rb_funcall(x, less_than, 1, y);

    if (NIL_P(c)) return Qtrue;
    if ( c == Qfalse ) return Qtrue;

    return Qfalse;
}
</code>

The only problem is that the following definition
<code>
static VALUE
ho_equal(x, y)
    VALUE x, y;
{
    VALUE c;

    if (x == y) return Qtrue;

    // x <= y ?
    c = rb_funcall(x, less_than, 1, y);
    if ( NIL_P(c) ) return Qfalse;
    if ( c == Qfalse ) return c;

    // y <= x ?
    c = rb_funcall(y, less_than, 1, x);
    if ( NIL_P(c) ) return Qfalse;
    if ( c == Qfalse ) return c;
    return Qtrue;
}
...
void
Init_HalfOrder()
{
    rb_mHalfOrder = rb_define_module("HalfOrder");
    rb_define_method(rb_mHalfOrder, "==", ho_equal, 1);
    rb_define_method(rb_mHalfOrder, ">", ho_gt, 1);
    rb_define_method(rb_mHalfOrder, ">=", ho_ge, 1);
    rb_define_method(rb_mHalfOrder, "<", ho_lt, 1);

    less_than = rb_intern("<=");
}
</code>
does not override the #== of the class we are mixed in.


I found no way to do this but I would love to do this.

Thank you
Robert
-- 
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.

- George Bernard Shaw