What you can do with macros in Lisp

[Kenny Tilton]

Tim Bradshaw wrote:

> Someone mentioned that there's been the usual futile argumentation
> between Lisp people and you-don't-need-macros-at-all and/or
> you-can-do-it-all-with-HOFs people.

The ancient context for this thread was a prior incarnation arising 
amongst Pythonistas discussing on clp whether or not Python should have 
macros in version 42, due out in fifteen years.

So I am adding clp in this otherwise unmodified version of your original.

Me, I finally realized two things: (a) Graham explains it better:

    http://www.paulgraham.com/onlisp.html

..and two, hey, one of Python's most important design principle is 
visually clean code. I think I use macros more for that than anything else.

kenny


> 
> Here's something I'd like to see non-macro people do.
> 
> Imagine you have a language with a CASE expression.  You're writing
> (or generating: for instance in the output of some kind of FSM system)
> code that has a huge number of large, dense, integer CASE expressions,
> which can obviously be optimised into jump-tables.  But your compiler
> won't do this, so your code is spending lots of time testing integers
> repeatedly.
> 
> So: implement NCASE, which looks exactly like your language's CASE
> expression, but, if all the keys are numeric and if they pass some
> user-definable test - for instance that there are enough keys and they
> are dense enough in their range, will expand to a jump-table.
> Otherwise it should just expand to the ordinary CASE expression.
> 
> Can you do this with macros in Lisp?  Yes: in fact I did this ages
> ago, with results I've now put up at
> http://www.tfeb.org/lisp/toys.html#NCASE.
> 
> Can you do it any other way (in partiucular: in any way which isn't
> equivalent to writing a macro system...)
> 
> --tim
> 
> 

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