From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>
Subject: Re: Adding wc to Bournish
Date: Tue, 14 Jun 2016 11:57:26 +0200
Message-ID: <idjeg80xfcp.fsf@bimsb-sys02.mdc-berlin.net>
References: <20160524184720.GA27449@debian-netbook>
	<20160605124033.GB859@debian-netbook> <87eg8bpe2v.fsf@gnu.org>
	<20160607074155.GB32264@debian-netbook>
	<878tyfelf6.fsf@gnu.org> <20160614092713.GA2832@debian-netbook>
Mime-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: quoted-printable
Return-path: <guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org>
Received: from eggs.gnu.org ([2001:4830:134:3::10]:33286)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <Ricardo.Wurmus@mdc-berlin.de>) id 1bCl86-0002G7-Rg
	for guix-devel@gnu.org; Tue, 14 Jun 2016 05:59:31 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <Ricardo.Wurmus@mdc-berlin.de>) id 1bCl82-0007DV-Mf
	for guix-devel@gnu.org; Tue, 14 Jun 2016 05:59:29 -0400
In-Reply-To: <20160614092713.GA2832@debian-netbook>
List-Id: "Development of GNU Guix and the GNU System distribution."
	<guix-devel.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/guix-devel>,
	<mailto:guix-devel-request@gnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/archive/html/guix-devel/>
List-Post: <mailto:guix-devel@gnu.org>
List-Help: <mailto:guix-devel-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/guix-devel>,
	<mailto:guix-devel-request@gnu.org?subject=subscribe>
Errors-To: guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org
Sender: "Guix-devel" <guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org>
To: Efraim Flashner <efraim@flashner.co.il>
Cc: guix-devel@gnu.org


Efraim Flashner <efraim@flashner.co.il> writes:

> +(define wc-command-implementation
> +  (lambda files
> +    (let ((files (filter (lambda (file)
> +                           (catch 'system-error
> +                             (lambda ()
> +                               (stat file))
> +                             (lambda args
> +                               (let ((errno (system-error-errno args))=
)
> +                                 (format (current-error-port) "~a: ~a~=
%"
> +                                         file (strerror errno))
> +                                 #f))))
> +                         files)))
> +      (for-each
> +        (lambda (file)
> +          (let-values (((lines chars)
> +                        (call-with-input-file file lines+chars)))
> +                      (format #t "~a ~a ~a~%" lines chars file)))
> +        files))))
> +
> +(define wc-l-command-implementation
> +  (lambda files
> +    (let ((files (filter (lambda (file)
> +                           (catch 'system-error
> +                             (lambda ()
> +                               (stat file))
> +                             (lambda args
> +                               (let ((errno (system-error-errno args))=
)
> +                                 (format (current-error-port) "~a: ~a~=
%"
> +                                         file (strerror errno))
> +                                 #f))))
> +                         files)))
> +      (for-each
> +        (lambda (file)
> +          (let-values (((lines chars)
> +                        (call-with-input-file file lines+chars)))
> +                      (format #t "~a ~a~%" lines file)))
> +        files))))
> +
> +(define wc-c-command-implementation
> +  (lambda files
> +    (let ((files (filter (lambda (file)
> +                           (catch 'system-error
> +                             (lambda ()
> +                               (stat file))
> +                             (lambda args
> +                               (let ((errno (system-error-errno args))=
)
> +                               (format (current-error-port) "~a: ~a~%"
> +                                       file (strerror errno))
> +                               #f))))
> +                         files)))
> +      (for-each
> +        (lambda (file)
> +          (let-values (((lines chars)
> +                        (call-with-input-file file lines+chars)))
> +                      (format #t "~a ~a~%" chars file)))
> +        files))))

It looks to me that the filter function is the same in all of these
procedures.  Even the actual implementation, i.e. the for-each over the
resulting files is almost exactly the same.

This could be simplified.  If only the format expression differs then
you could abstract this difference away.  You could still have three
different procedures, but they can be the result of evaluating a
higher-order function.

It also seems to me that you could use syntactic sugar to simplify
=E2=80=9C(define something (lambda ...))=E2=80=9D to =E2=80=9C(define (so=
mething ...))=E2=80=9D.

~~ Ricardo