From: ptkwt@... (Phil Tomson)
Date: 2006-02-18T05:18:38+09:00
Subject: Re: recontextualizing a block (looking for deep magic)

In article <45lhnsF707hgU1@individual.net>,
Robert Klemme <bob.news@gmx.net> wrote:
>Phil Tomson wrote:
>
>How ugly do you feel about
>
>define_behavior {|in,out,var|
>  if in[:rst]
>    var[:count]=0
>  elsif in[:clk]
>    var[:count]+=1
>  end
>}

I'd rather just go ahead and use the '@'.

>
>This has the added benefits of
>
> - giving you the choice what to provide as arguments (could be simply
>hashes but anything else that supports the interface)
>
> - introducing separate namespaces for each type of variable
>
>But then again, using plain instance variables might be even simpler and
>less cluterrish...
>
>> So that's why I was trying to dynamically create a method that would
>> have the variables in the scope of the method and then the proc bound
>> to that scope.
>>
>> I suppose another way to do it would be to do:
>>
>>   class Counter < RHDL
>>     inputs    :clk, :rst
>>     outputs   :count_out
>>
>>     def initialize
>>       count = 0
>>       define_behavior {
>>         #.... do something with count ...
>>       }
>>     end
>>   end
>>
>> This is sort of how RHDL is now.  There's no need for a 'variables'
>> method since you just declare your variables in the 'initialize'
>> method.  I was trying to get away from the explicit 'initialize'
>> definition.  But maybe it's not such a bad thing.  'count' would then
>> be available to the block passed to define_behavior.
>
>IMHO explicit is not bad.  Often it makes code more readable and
>maintainable.

True, but.... but since this is a DSL it seems to add a bit of clutter.  With 
the other 'syntax' shown earlier, the 'initialize' method is generated 
automatically so that it takes the inputs and outputs:

  ag = AndGate.new(a,b,result)

that seems kind of nice...

>
>> The other alternative is the one that Jim Freeze mentioned:
>>
>>   class Counter < RHDL
>>     inputs    :clk, :rst
>>     outputs   :count_out
>>     variables :count=>0, :foo=>42
>>
>>     define_behavior %q{
>>       #.... do something with count, foo ...
>>     }
>>   end
>>
>> In that case defne_behavior takes a string instead of a block.  That
>> solves the problem because the string can be evaluated later in
>> different contexts.
>> But the '%q' is kind of ugly ;-)
>
>Yes. :-)

....but it could be the least of the evils.

Phil