Re: Appropriate case for a macro?
- From: Chris Riesbeck <Chris.Riesbeck@xxxxxxxxx>
- Date: Mon, 31 Mar 2008 12:31:18 -0500
Brian Adkins wrote:
I program primarily in Ruby and have been trying to find time to learn
Lisp. One of the things that attracts me to Lisp is the macro
facility. Consider the following pattern:
if a_long_expression > value
foo(a_long_expression)
bar(a_long_expression)
else
baz(a_long_expression)
end
This can be made more concise via an assignment:
if (x = a_long_expression) > value
foo(x)
bar(x)
else
baz(x)
end
However, this seems like a pragmatic hack since a new variable is
introduced simply for conciseness. Would you consider this an
appropriate case for a macro in Common Lisp?
Certainly if you're going to do it, you'd do it with macros. Whether you should do it is a matter of debate.
Perhaps used as follows:
(my-if (> a-long-expression value)
(progn
(foo lhs)
(bar lhs))
(baz lhs))
where a-long-expression has been replaced by lhs
See Anaphoric Macros for a common approach to this:
http://www.bookshelf.jp/texi/onlisp/onlisp_17.html#SEC111
.
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