Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!aero!srt
From: srt@aerospace.aero.org (Scott "TCB" Turner)
Newsgroups: comp.lang.lisp
Subject: Re: AKCL declarations
Message-ID: <93512@aerospace.AERO.ORG>
Date: 5 Dec 90 18:04:30 GMT
References: <127126@linus.mitre.org>
Organization: The Aerospace Corporation, El Segundo, CA
Lines: 50
Keywords:

Try:

	(proclaim '(function foo (fixnum) fixnum))
	(defun foo (x)
	  (declare (fixnum x))
	  (the fixnum (* x x)))

That should produce what you expect.  I went through this whole
business a few months ago.  It can be tricky to figure out exactly
what declarations AKCL needs to perform optimizations, but you rarely
can go wrong if you declare everything in sight.  Once you get the
hang of it, it becomes obvious what you need.

In this case, I think you are a little confused over declarations inside
a function and outside the function.  For example, 

	(defun test4 (x)
	  (declare (fixnum x))
	  (the fixnum (* x x)))

This declaration does *not* tell AKCL that test4 will be called with a
fixnum argument.  What it says is that *test4* assumes that the
argument will be a fixnum.  So AKCL generates code on the assumption
that x could be anything, and needs to be turned into a fixnum.

The proclaim tells AKCL about how a function will be called.  The 
proclamation

	(proclaim '(function test4 (fixnum) fixnum))

tells AKCL that the arguments to test4 will be fixnums and that the 
returned result will also be a fixnum.

Incidentally, if you are worried about speed, I've found that the three
biggest factors in AKCL code are:

	(1) GC.  My personal experience has been that frequent
	small GCs win *big* over infrequent large GCs.  (On a Sun
	4/110.)

	(2) Explicit operations wherever possible.  Avoiding object
	conversions and generic functions is not only much faster,
	but it greatly reduces the amount of garbage generated.  
	"Foo" with the fixnum declarations above produces *no* 
	garbage.  Without it generates three ephemeral objects.

	(3) Declaration of functions with fixed arguments.  In AKCL,
	function calls of fixed arguments are much faster than 
	generic function calls.

					-- Scott Turner


Brought to you by Super Global Mega Corp .com