Subject: Re: merits of Lisp vs Python
From: (Rob Warnock)
Date: Mon, 18 Dec 2006 05:08:20 -0600
Newsgroups: comp.lang.lisp,comp.lang.python
Message-ID: <>
<> wrote:
| Paul Rubin wrote:
| > [...]  There are programs you can write in C but not in Lisp,
| > like device drivers that poke specific machine addresses.
| I should assume you meant Common Lisp, but there isn't really any
| reason you couldn't
|      (poke destination (peek source))
| in some version of Lisp that was meant for writing device drivers
| (perhaps under a Lisp machine or something).

I do this kind of thing *every day* in CMUCL!! It's my primary
user-mode hardware debugging tool. Here's a typical utility function:

    ;;; Used for things like polling for a "done" flag.
    ;;; BUG: Assumes contents of ADDR will change within fixnum polls.
    (defun spin-until-change (addr)
      (declare (optimize (speed 3) (debug 0) (safety 0)))
      (loop with v0 of-type (unsigned-byte 32) = (r32 addr)
	    with counts fixnum = 0
	    while (= v0 (r32 addr))
	 do (setf counts (the fixnum (1+ counts)))
	 finally (return counts)))

| SIOD actually has (%%% memref address) for peek.

CMUCL has SYSTEM:SAP-REF-{8,16,32} and SETFs of same. The R32
above is just my convenience wrapper around SYSTEM:SAP-REF-32:

    (declaim (inline r32))

    (defun r32 (addr)
      (declare (optimize (speed 3) (debug 0) (safety 0)))
      (system:sap-ref-32 (system:int-sap addr) 0))

    (defun w32 (addr &rest values)
      (declare (optimize (speed 3) (debug 0) (safety 0)))
      (loop for i fixnum from 0 by 4
	    and v of-type (unsigned-byte 32) in values
	do (setf (system:sap-ref-32 (system:int-sap addr) i) v))

Most other Common Lisp implementations surely have something similar.


Rob Warnock			<>
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