From: Paul Brannan <pbrannan@...>
Date: 2004-08-06T05:30:39+09:00
Subject: Re: Macros in Ruby

On Fri, Aug 06, 2004 at 04:18:41AM +0900, David A. Black wrote:
> which bugs me in some way involving levels of indirection that I can't
> quite put my finger on....

The way I see it, & and unary * (and possibly in the future unary **)
are related operators in the sense that they transform their argument to
or from a particular representation.

For example, *array transforms array into a list inline, so that an
array can be turned into an argument list for use in passing to a
method.  However, *param in a method definition takes a list of
arguments and transforms it into an array.  Similarly, it has been
proposed to have **hash turn hash into a list of named arguments, and
**param in a method definition to be used to transform unused named
arguments into a hash.  A similar symmetry exists with the & operator;
when called using &proc it turns a proc object into a block and when
used in a method's paramter list it turns a passed block back into a
proc object.

Using &{ ... } as a shorthand for creating proc objects would break this
symmetry.  We do currently use * and ** for both the above uses and for
multiplication/exponentiation, but with these operations it is the
binary versions of the operator, not the unary one, so there is no break
in symmetry.

Paul