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From: Patricia Ferreira <pferreira@example.com>
Newsgroups: pt.comp.programacao
Subject: Re: sobre loops em common lisp
Date: Fri, 08 Mar 2024 17:12:25 -0300
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Patricia Ferreira <pferreira@example.com> writes:

> Patricia Ferreira <pferreira@example.com> writes:
>
>> Patricia Ferreira <pferreira@example.com> writes:
>>
>> [...]
>>
>>> Eis meu segundo.  Gere um nome (de arquivo) aleatório e tente usá-lo.
>>> Se calhar de alguém já tê-lo escolhido, tente de novo (com outro nome).
>>> Feito isso, retorne-nos esse nome sortudo e pra que a gente possa
>>> renomeá-lo pro seu nome final---accounts.lisp.
>>>
>>> (defun write-accounts ()
>>>   (let ((name
>>>           (loop 
>>>             (let* ((tmp (random-string 10))
>>>                    (name (format nil "~a.tmp" tmp)))
>>>               (when 
>>>                   (ignore-errors 
>>>                    (with-open-file 
>>>                        (s name
>>>                           :direction :output
>>>                           :if-exists :error
>>>                           :if-does-not-exist :create)
>>>                      (write *accounts* :stream s)))
>>>                 (return name))))))
>>>     (rename-file name "accounts.lisp")
>>>     *accounts*))
>>>
>>> Tecnicamente temos um problema com esse procedimento.  Se o rename-file
>>> não obtiver sucesso, nem vamos saber.
>>
>> Não sei o que fazer se o rename não ocorrer, mas ficamos a versão final:
>>
>> (defun write-accounts ()
>>   (let ((name
>>           (loop 
>>             (let* ((tmp (random-string 10))
>>                    (name (format nil "~a.tmp" tmp)))
>>               (when 
>>                   (ignore-errors 
>>                    (with-open-file 
>>                        (s name
>>                           :direction :output
>>                           :if-exists :error
>>                           :if-does-not-exist :create)
>>                      (write *accounts* :stream s)))
>>                 (return name))))))
>>     (if (ignore-errors (rename-file name "accounts.lisp"))
>>         *accounts*
>>         (format t "could not rename ~a to account.lisp" name))))
>
> Lol.  Não é isso que quero, não.  O que quero é:
>
> (defun write-accounts ()
>   (let ((name
>           (loop 
>             (let* ((tmp (random-string 10))
>                    (name (format nil "~a.tmp" tmp)))
>               (when 
>                   (ignore-errors 
>                    (with-open-file 
>                        (s name
>                           :direction :output
>                           :if-exists :error
>                           :if-does-not-exist :create)
>                      (write *accounts* :stream s)))
>                 (return name))))))
>     (if (ignore-errors (rename-file name "accounts.lisp"))
>         *accounts*
>         (format nil "could not rename ~a to accounts.lisp" name))))
>
> PACKAGE> (write-accounts)
> "could not rename wqjjpdlifi.tmp to accounts.lisp"
>
> Agora sim.

Lol.  Eis meu terceiro loop.

(defun size-of-longest-username ()
  (loop for u in *accounts*
        maximizing (length (account-username u))))

Escrevi isso sem nem ter que olhar nada pra relembrar.  Estou gostando
de loop.  Esse é o fato.  De fato são coisas que a gente faz muito.  A
comunidade Lisp tem sabedoria aí.