From: User Name <martin@...>
Date: 2006-08-29T06:34:22+09:00
Subject: Re: Need - macros feature

Henry Savr <hsavr@yahoo.com> writes:

> <a desire for macros in ruby>

What about this?  It's still a far cry from lisp macros, as it only
lets you define macros that work at the module level, and you need to
appropriately quote the input to a macro yourself, but I think with a
bit more reworking we could get "macros" to work at whatever level was
desired.

class Module
  def defmacro(symbol, &block)
    methodproc = Proc.new {|*a|self.class_eval(block.call(*a))}
    self.send(:define_method, symbol, methodproc)
  end

  # Example macro that does what was mentioned in the long request:

  defmacro(:var){|name,init|%Q{
    def #{name}
      @#{name} = #{init.inspect} unless defined? @#{name}
      @#{name}
    end
    def #{name}=(val)
      @#{name}=val
    end
  }}

  # A silly macro - creates some number of attributes all
  # with the same prefix, and initial values nil

  defmacro(:varfamily){|name,n|
    (1..n).map{|i|"var :#{name}_#{i}"}.join("\n")
  }
end


Now let's test this out:

irb(main):033:0> class Foo; varfamily :foo,10; end
=> nil
irb(main):034:0> g = Foo.new
=> #<Foo:0x299b668>
irb(main):036:0> g.methods.select{|m|m=~/^foo/}.sort
=> ["foo_1", "foo_10", "foo_10=", "foo_1=", "foo_2", "foo_2=",
"foo_3", "foo_3=", "foo_4", "foo_4=", "foo_5", "foo_5=", 
"foo_6", "foo_6=", "foo_7","foo_7=", "foo_8", "foo_8=", 
"foo_9", "foo_9="]
irb(main):037:0> g.foo_5
=> nil
irb(main):038:0> g.foo_5=6
=> 6
irb(main):039:0> g.foo_5
=> 6

I still think that you're almost always better off using some already
present meta-programming tool, but if you really want a string-parsing
macro soup, this might do the trick.

-- 
s=%q(  Daniel Martin -- martin@snowplow.org
       puts "s=%q(#{s})",s.map{|i|i}[1]       )
       puts "s=%q(#{s})",s.map{|i|i}[1]