From: Logan Capaldo <logancapaldo@...>
Date: 2006-08-29T03:18:26+09:00
Subject: Re: Need - macros feature


On Aug 28, 2006, at 1:11 PM, Henry Savr wrote:

> Matthew Johnson wrote:
>>> Thank you, guys
>>> Although it's not what I wanted, I have a lot of ideas in some
>>> directions. It's good for new in Ruby.
>>> Henry
>>
>> Can you describe some of your ideas?  That would certainly help
>> foster discussion...
>>
>> Matthew
>
> There is nothiing new. It's as old as Univac
> What I want is a classic Macroprocessor tool.
> I mean:
> I keep pieces of souce code in some place.
> They may be included in source code as is. More interesting, you can
> adjust macroprocessor's output (hence, the input for Ruby interpeter)
> using paremters.
>
> E X A M P L E:
> ===============
> You wrote the macro once and put it in macro library
> (here I "invented" the "macrolanguage" on-fly, while writing the
> example. I  hope, the "language" is clear)
>
> ====this is a macro %var with argument %%x definition==============
> macro: %var (%%x)
>
> {def %%x=(value)
> 	@%%x = value
> 	return @%%x
> end}
> ======== end of macro %var definition =============================
> You may consider the macro definition as a template.
>
>
> Now, somewhere in your code you write:
> ...
> %var(my_lovely_var)
> ...
>
> Once found the %var, macroprocessor should make substitutions and
> produce this piece:
>
> def my_lovely_var=(value)
> 	@my_lovely_var = value
> 	return @my_lovely_var
> end
>
> which will be inserted into code on the place, where the statement
> %var(my_lovely_var) was instead of it.
>
>
>
> Ruby style allows to expect, that it may be done on-fly.
>
> So, finally the Ruby interpreter will execute the macroprocessor's
> output, not input. Besides the macroprocessor's input and output are
> saved, so you can return to them and change the simple lines of
> get/set-code to something more complicated and valueable.
>
> Again the get/set operations are just an EXAMPLE, used because  
> everyone
> is familiar with this piece of code. Sure, using attributes is kind of
> solution for this particular case. (BTW. Thank you, Farrel Lifson, you
> post convinced me to learn more about attributes on this very  
> beginning
> stage, and that was very usefull). I want the macro power options
> themselves.
>
I think maybe you underestimate what can be done with meta  
programming in ruby that (almost) obviates the need for macros.

class Module
   # "macro" definition
   def var(symbol)
     define_method("#{symbol}=") { |value| instance_variable_set("@# 
{symbol}", value) }
   end
end

class A
   var :my_lovely_var
end
a = A.new
a.my_lovely_var = 1

Maybe if you can come up with a less trivial example, you can stump  
us, but I doubt it.

> Posted via http://www.ruby-forum.com/.
>