From: Pat Maddox <pergesu@...>
Date: 2006-06-03T21:52:20+09:00
Subject: Can you do Lisp-like macros in Ruby?

I've never used lisp before until ~2am last night...and while working
on the very simple unit testing framework in Practical Common Lisp [1]
I came up with this macro:

(defun report-result (result form)
 (format t "~:[FAIL~;pass~] ... ~a~%" result form))

(defmacro test (test-form)
 (let ((result (gensym)))
   `(let ((,result ,test-form))
      (report-result ,result ',test-form)
      ,result)))

Using that macro, I can do:
CL-USER> (test (= (+ 1 2) 3))
pass ... (= (+ 1 2) 3)
T

I really like the syntax of that.  How could I do the same thing in
Ruby?  I took a quick shot and missed...it might be super easy and I'm
just dumb from this apparent insomnia.  I really like using Ruby, but
I would absolutely love it if I could build syntax like I did with
Lisp.

The Ruby translation of the syntax - not the code that actually makes
it work - would be like

irb> test { (1 + 2) == 3 }
pass ... (1 + 2) == 3

Okay here's what I've come up with:

def report_result(result, &block)
 message = result ? "pass" : "FAIL"
 puts "#{message} ... #{block}"
end

def test(&block)
 result = yield
 report_result result, &block
 result
end

irb> test { (1 + 2) == 3 }
pass ... #<Proc:0x00306b58@(irb):55>

So I guess the question is how to make the code show up.

Here's my change:

def report_result(result, code)
 message = result ? "pass" : "FAIL"
 puts "#{message} ... #{code}"
end

def test(code)
 result = eval code
 report_result result, code
 result
end

irb> test "(1 + 2) == 3"
pass ... (1 + 2) == 3

I certainly don't like sticking my code in a string like that.  That
just kind of sucks.

Over all this is kind of a lame example anyway.  Just after spending
some time with Lisp though, I get the feeling that I'll be able to do
some really cool stuff with it, stuff that I don't know how to do in
Ruby, despite using Ruby for several months now.  I don't know exactly
what it is, but somehow I know that - at least with the Ruby coding
style I used above - I won't be able to do some things with Ruby that
I would be able to in Lisp.  I appreciate any feedback...hopefully you
guys don't think I'm out in left field with this.

Pat

[1] http://www.gigamonkeys.com/book/