Re: need for macros (was Re: Icon)

[Matthias Felleisen <address@hidden>]

Scheme 84 had this, and I don't see why this isn't in most Lisps. 

Still, I believe that some features should not be in programming languages
because neither the designers nor the super programmers nor the average
programmers know how to reason about them systematically. I have come to
believe that 3D macros are one such thing. They co-mingle two radically
different phases: compilation and execution. You cannot possibly deploy a
program that is expanded like that on a different machine. The very idea
doesn't make sense. I guess in short, I believe in the strict separation of
passes. Otherwise I am open to pretty much everything :-) 

-- Matthias

  > Date: Fri, 21 Dec 2001 15:38:55 -0800 (PST)
  > From: Paul Graham <paulgraham@yahoo.com>
  > Cc: ll1-discuss@ai.mit.edu
  > Content-Type: text/plain; charset=us-ascii
  > 
  > 
  > --- Matthias Felleisen <matthias@ccs.neu.edu> wrote:
  > > 
  > > Yes, Dan used to assign this as a puzzle in 1983/84 and I posed it to
  > > Guy
  > > at my first POPL: it's called ONCE. You are creating a 3-dimensional
  > > value
  > > that tunnels its way from expansion to run-time. Is this a good
  > > thing? 
  > 
  > Sure, why not?  It solves my problem in this case, and solving
  > problems is what language are for.  
  > 
  > In Arc it is explicitly part of the language that you can insert
  > objects (not just expressions) into macroexpansions.  Also 
  > that anything that isn't a list or a symbol evaluates to itself.
  > 
  > I'm not sure if/which other Lisps have done this before, but
  > it gives you a small but significant boost in expressive power.
  > It may also help make programs faster, because it means you
  > can build things at compile time that would otherwise have to
  > be built at runtime.
  > 
  > Of course if people don't want to do this they don't have to.
  > Arc's philosophy is, let the programmer decide.
  > 
  > --p "Arc: It's not just free, it's libertarian!" g
  > 
  > 
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