[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
PROG1 as a function
Date: Wed, 4 Jan 89 14:17 EST
From: Michael Greenwald <Greenwald@stony-brook.scrc.symbolics.com>
Date: Wed, 4 Jan 89 13:49 EST
From: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>
Date: Tue, 3 Jan 89 20:10 EST
From: Barry Margolin <barmar@Think.COM>
One of our users noticed today that Symbolics defines PROG1 as a
function, rather than as a macro as CLtL specifies. The definition is
(defun prog1 (first-form &rest rest-forms)
(declare (ignore rest-forms))
This works because CL requires left-to-right evaluation of function
CLtL is vague about the order of evaluation of function arguments. In
chapters 5 and 7 it neither says that the order is left-to-right nor
that the order is undefined, and I suspect that the person who made
PROG1 a macro thought the order was undefined; I can't see any other
reason that it would need to be a macro. The place in CLtL that says
that all function arguments are evaluated left-to-right is page 194,
buried in the middle of a discussion on numeric contagion.
Actually, CLtL pg 61 says that the arguments and parameters are
processed in order, from left to right. I don't know if "processed"
implies "evaluated", but I always assumed (perhaps incorrectly) it did.
I interpret this as referring to how the (fully evaluated) arguments
are processed during lambda-binding, not to the order in which argument
forms in a function call are evaluated. After all, the arguments referred
to on page 61 might have come from a list given to APPLY, rather then
from EVAL on a function call.