From: Yehuda Katz <wycats@...>
Date: 2008-12-03T02:36:18+09:00
Subject: [ruby-core:20214] Proposal: deferred blocks

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Several people have played around with solutions that use ParseTree or
RubyParser to extract the contents of a lambda and perform certain
operations.
For instance,

Article.select {|a| a.title =~ /Some title/ }

would generate "select * from articles where title ~ 'Some title'"

This requires access to the ParseTree at runtime, which requires converting
a proc to a ParseTree at runtime. I've been toying with the idea of an
explicit language feature, like lisp quoting, that would explicitly pass the
ParseTree to the method called.

Example:

Article.select(defer {|a| a.title =~ /Some title/ })

class Article
  def self.select(sexp)
    # sexp is: s(:defer, s(:lasgn, :a), s(:match3, s(:lit, /Some title/),
s(:call, s(:lvar, :a), :title, s(:arglist))))
  end
end

I understand that this would require a more explicit definition of the parse
tree, but it seems like UnifiedRuby has provided a viable starting point for
that work.

Is this a terrible idea? Has it already been proposed and rejected
innumerable times?

-- 
Yehuda Katz
Developer | Engine Yard
(ph) 718.877.1325

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Several people have played around with solutions that use ParseTree or RubyParser to extract the contents of a lambda and perform certain operations.<div><br></div><div>For instance,</div><div><br></div><div>Article.select {|a| a.title =~ /Some title/ }</div>
<div><br></div><div>would generate &quot;select * from articles where title ~ &#39;Some title&#39;&quot;</div><div><br></div><div>This requires access to the ParseTree at runtime, which requires converting a proc to a ParseTree at runtime. I&#39;ve been toying with the idea of an explicit language feature, like lisp quoting, that would explicitly pass the ParseTree to the method called.</div>
<div><br></div><div>Example:</div><div><br></div><div>Article.select(defer {|a| a.title =~ /Some title/ })</div><div><br></div><div>class Article</div><div>&nbsp;&nbsp;def self.select(sexp)</div><div>&nbsp;&nbsp; &nbsp;# sexp is:&nbsp;s(:defer, s(:lasgn, :a), s(:match3, s(:lit, /Some title/), s(:call, s(:lvar, :a), :title, s(:arglist))))</div>
<div>&nbsp;&nbsp;end</div><div>end<br clear="all"><br></div><div>I understand that this would require a more explicit definition of the parse tree, but it seems like UnifiedRuby has provided a viable starting point for that work.</div>
<div><br></div><div>Is this a terrible idea? Has it already been proposed and rejected innumerable times?</div><div><br>-- <br>Yehuda Katz<br>Developer | Engine Yard<br>(ph) 718.877.1325<br>
</div>

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