Re: Lisp reader syntax and bootstrap

[Paul Eggert <eggert@cs.ucla.edu>]

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On 2023-07-13 22:05, Ulrich Mueller wrote:
> Maybe some wording like "approximates positive and negative infinities
> with the largest and smallest representable finite numbers" would be
> more accurate?

Unfortunately "smallest" connotes being close to zero. Also, I just 
looked at the C Standard again, and it doesn't guarantee that HUGE_VAL 
is the maximum 'double' on a VAX (!).

Anyway, thanks for pointing out the confusion. I installed the attached 
to try to clear matters up.

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From be501f468ed36cddf01305b88bab44366b447c03 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 13 Jul 2023 23:36:33 -0700
Subject: [PATCH 1/2] Improve doc for VAX reading NaN, INF

* doc/lispref/numbers.texi (Float Basics): Improve description of
how Lisp reads infinities and NaNs on a VAX.
---
 doc/lispref/numbers.texi | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi
index bcf89fc9ab1..a49afb73539 100644
--- a/doc/lispref/numbers.texi
+++ b/doc/lispref/numbers.texi
@@ -280,9 +280,9 @@ Float Basics
 @code{(= 0.0 -0.0)} returns @code{t}.
 
   Infinities and NaNs are not available on legacy systems that lack
-IEEE floating-point arithmetic.  On a circa 1980 VAX, for example, the
-Lisp reader approximates an infinity with the nearest finite value,
-and a NaN with some other non-numeric Lisp object that provokes an
+IEEE floating-point arithmetic.  On a circa 1980 VAX, for example,
+Lisp reads @samp{1.0e+INF} as a large but finite floating-point number,
+and @samp{0.0e+NaN} as some other non-numeric Lisp object that provokes an
 error if used numerically.
 
 Here are read syntaxes for these special floating-point values:
-- 
2.39.2


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From 01b80a6f0e40a4390717a79a73c61899e2ec2968 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 13 Jul 2023 23:55:50 -0700
Subject: [PATCH 2/2] Reorder NaN, INF paras

* doc/lispref/numbers.texi (Float Basics):
Reorder paragraphs so that examples follow defns.
---
 doc/lispref/numbers.texi | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi
index a49afb73539..071ec0f518d 100644
--- a/doc/lispref/numbers.texi
+++ b/doc/lispref/numbers.texi
@@ -279,12 +279,6 @@ Float Basics
 conversely, @code{(equal 0.0 -0.0)} returns @code{nil} whereas
 @code{(= 0.0 -0.0)} returns @code{t}.
 
-  Infinities and NaNs are not available on legacy systems that lack
-IEEE floating-point arithmetic.  On a circa 1980 VAX, for example,
-Lisp reads @samp{1.0e+INF} as a large but finite floating-point number,
-and @samp{0.0e+NaN} as some other non-numeric Lisp object that provokes an
-error if used numerically.
-
 Here are read syntaxes for these special floating-point values:
 
 @table @asis
@@ -294,6 +288,12 @@ Float Basics
 @samp{0.0e+NaN} and @samp{-0.0e+NaN}
 @end table
 
+  Infinities and NaNs are not available on legacy systems that lack
+IEEE floating-point arithmetic.  On a circa 1980 VAX, for example,
+Lisp reads @samp{1.0e+INF} as a large but finite floating-point number,
+and @samp{0.0e+NaN} as some other non-numeric Lisp object that provokes an
+error if used numerically.
+
   The following functions are specialized for handling floating-point
 numbers:
 
-- 
2.39.2