ERB as a macro pre-processor?

ruby-talk
1

"The Ruby Way" (pp. 43-45) shows a couple of different ways
to generate methods dynamically (using eval). Looking at the
examples, I began to wonder about different Ways To Do It.

One possibility that occurred to me is to use ERB as a macro
pre-processor. The book suggests the following code:

  if platform == Windows
    def my_action
      action1
    end
  if platform == Linux
    def my_action
      action2
    end
  else
    def my_action
      default_action
    end
  end

Although this is approach is direct and simple, it seems like it
wouldn't scale very well, given multiple variations. However, I
think that the following approach might:

% cat erb_ml
#!/usr/bin/env ruby

  require 'erb'

  def action_D; print "default action\n"; end
  def action_L; print "Linux action\n"; end
  def action_W; print "Windows action\n"; end

  action = { :Linux => 'action_L',
             :Windows => 'action_W' }

  template = ERB.new <<-EOF
    def my_action
      <%= action[platform] || 'action_D' %>
    end
  EOF

  for platform in [ :Linux, :Windows, :Plan9 ] do
    eval template.result(binding)
    print "#{platform.to_s}: "
    my_action
  end

% erb_ml
Linux: Linux action
Windows: Windows action
Plan9: default action

Obviously, the "action" hash could be replaced by other
code-generation and/or -retrieval methods. Is anyone
here using ERB in this manner? Are there any caveats
or alternative approaches that I should be aware of?

-r

···

--
http://www.cfcl.com/rdm Rich Morin
http://www.cfcl.com/rdm/resume rdm@cfcl.com
http://www.cfcl.com/rdm/weblog +1 650-873-7841

Technical editing and writing, programming, and web development

2

Bah I say! How does that saying go, "Replace conditionals with
polymorphism"?

class Platform
end

class Linux < Platform
  def define_methods
    def a
      puts "linux"
    end
  end
end

class Windows < Platform
  def define_methods
    def a
      puts "windows"
    end
  end
end

class Platform
  def self.get_platform
    case RUBY_PLATFORM
      when /linux/
        Linux
      when /win32/
        Windows
     end
  end
end

platform = Platform.get_platform.new
platform.define_methods

···

On Wed, Oct 11, 2006 at 02:40:58PM +0900, Rich Morin wrote:

"The Ruby Way" (pp. 43-45) shows a couple of different ways
to generate methods dynamically (using eval). Looking at the
examples, I began to wonder about different Ways To Do It.

One possibility that occurred to me is to use ERB as a macro
pre-processor. The book suggests the following code:

  if platform == Windows
    def my_action
      action1
    end
  if platform == Linux
    def my_action
      action2
    end
  else
    def my_action
      default_action
    end
  end

Although this is approach is direct and simple, it seems like it
wouldn't scale very well, given multiple variations. However, I
think that the following approach might:

% cat erb_ml
#!/usr/bin/env ruby

  require 'erb'

  def action_D; print "default action\n"; end
  def action_L; print "Linux action\n"; end
  def action_W; print "Windows action\n"; end

  action = { :Linux => 'action_L',
             :Windows => 'action_W' }

  template = ERB.new <<-EOF
    def my_action
      <%= action[platform] || 'action_D' %>
    end
  EOF

  for platform in [ :Linux, :Windows, :Plan9 ] do
    eval template.result(binding)
    print "#{platform.to_s}: "
    my_action
  end

% erb_ml
Linux: Linux action
Windows: Windows action
Plan9: default action

Obviously, the "action" hash could be replaced by other
code-generation and/or -retrieval methods. Is anyone
here using ERB in this manner? Are there any caveats
or alternative approaches that I should be aware of?

3

"The Ruby Way" (pp. 43-45) shows a couple of different ways
to generate methods dynamically (using eval). Looking at the
examples, I began to wonder about different Ways To Do It.

<snip>

Obviously, the "action" hash could be replaced by other
code-generation and/or -retrieval methods. Is anyone
here using ERB in this manner? Are there any caveats
or alternative approaches that I should be aware of?

http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/4e2f0f29308c9647/d985a8bf050d88d5?lnk=gst&q=r4&rnum=1#d985a8bf050d88d5

i did quite a bit more work on it but never released...

cheers.

-a

···

On Wed, 11 Oct 2006, Rich Morin wrote:
--
my religion is very simple. my religion is kindness. -- the dalai lama

4

interesting stuff; why not put out a WIP snapshot?

Both r4 and ERB allow the use of arbitrary Ruby code. It
would be interesting to see which features of each work
better for what kinds of problems.

-r

···

At 11:36 PM +0900 10/11/06, ara.t.howard@noaa.gov wrote:

i did quite a bit more work on it but never released...

--
http://www.cfcl.com/rdm Rich Morin
http://www.cfcl.com/rdm/resume rdm@cfcl.com
http://www.cfcl.com/rdm/weblog +1 650-873-7841

Technical editing and writing, programming, and web development