From: Kenichi Asai <email@example.com>
To: "Daniel Bünzli" <firstname.lastname@example.org>
Cc: Gabriel Scherer <email@example.com>, firstname.lastname@example.org
Subject: Re: [Caml-list] string_of_float (0.1 +. 0.2)
Date: Thu, 16 Jun 2022 10:45:58 +0900 [thread overview]
Message-ID: <YqqLVsxjHWWiA51Y@pllab.is.ocha.ac.jp> (raw)
Thank you all for the information.
> Nathanaëlle Courant, with help from Julien Lepiller and myself, wrote a
> rather complete interpreter/evaluator for OCaml parsetrees (in OCaml) as
> part of the Camlboot project
Yes, I read the programming paper. That's an interesting project.
> Kenichi, I don't understand what your own constraints, but
> in general I have the impression that "float" is better than "string"
> to represent double values used for computation.
I am developing an OCaml stepper that executes an OCaml program step
by step. From the OCaml parsetree for
let a = 0.1 +. 0.2 +. 0.4
I want an OCaml parsetree for
let a = 0.3 +. 0.4
let a = 0.300000000000000044 +. 0.4
if this is what OCaml uses internally. I want to produce an OCaml
parsetree rather than my own parsetree that maintains float as is,
because I could then reuse pretty printer of OCaml.
From Andreas' e-mail, I understand what's happening. (Thank you!) I
thought I would use Printf.sprintf "%.18g" in place of string_of_float,
but Daniel's e-mail made me think it could be insufficient, because
even if I use .18 (or .24), it is still an approximation of the float.
(Am I correct?) I tried to use `Format.sprintf "%h"` in place of
string_of_float, but the OCaml pretty printer produces
let a = 0x1.3333333333334p-2 +. 0.4
which is not suitable for a stepper used by novice programmers. For
now, I think I will use Printf.sprintf "%.18g" and see if students see
any difference between OCaml execution and stepper execution.
I agree with Francois that it would be nice if the OCaml manual could
mention a potential loss of information. I first thought that
replacing "%.12g" with "%.18g" solves the problem, but "the" string
representation of a float turned out to be more complicated than I
Thank you all for the discussion!
next prev parent reply other threads:[~2022-06-16 1:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 1:59 Kenichi Asai
2022-06-15 6:22 ` Andreas Rossberg
2022-06-15 7:00 ` François Pottier
2022-06-15 14:07 ` Gabriel Scherer
2022-06-15 14:25 ` Daniel Bünzli
2022-06-16 1:45 ` Kenichi Asai [this message]
2022-06-16 6:24 ` Oleg
2022-06-16 9:01 ` Andreas Rossberg
2022-06-16 9:14 ` [Caml-list] unsubscribe Jean-Denis EIDEN JEAN-DENIS
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).