From: Mat Schaffer <schapht@...>
Date: 2006-06-04T00:19:27+09:00
Subject: Re: Can you do Lisp-like macros in Ruby?

On Jun 3, 2006, at 8:52 AM, Pat Maddox wrote:
> 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/

It seems like just giving a Proc a copy of the code used to create it  
would do this.  There might even be a nice way to do it behind the  
scenes that wouldn't require actually storing a string.  But I don't  
see any way to do this myself right now.  Maybe some tricks with  
stack tracing?
I do agree that Lisp has some neat tricks, but it made my eyes hurt  
trying to figure out where all the parens in that code started and  
stopped....
-Mat