From: John Mastro <john.b.mastro@gmail.com>
To: "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
Subject: Fwd: How to check whether a character (or one-character string) is a letter?
Date: Fri, 3 Oct 2014 19:47:39 -0700 [thread overview]
Message-ID: <CAOj2CQS_5PFwoGn-c0AELNe_Q4xUdgGryHC9Zgp7iKVKtox7iw@mail.gmail.com> (raw)
In-Reply-To: <CAOj2CQQsnNxtUPzPV8Vw_DgfGFXUUkZExHbArAu_zDjQn-prvw@mail.gmail.com>
[I first sent this directly to Marcin in error - yeah, I use the email gateway]
Hi Marcin,
Marcin Borkowski <mbork@wmi.amu.edu.pl> wrote:
> Assume that I have a character (taken from some string, which in turn is
> copied from the buffer - so it need not be ASCII). What is the best way
> to check whether it is a letter within ASCII range?
>
> The reason I'm asking is that I'm writing a function which converts an
> arbitrary string to a valid (and nice) filename (e.g., only letters and
> hyphens) - so basically I want to walk a string character by character
> and convert any space to a hyphen and omit any other non-letter. Am I
> reinventing the wheel?
There are a bunch of ways to do this, but one reasonable approach is to
use a regular expression. I think this will do what you want:
(defun reasonable-filename (str)
(let* ((str (replace-regexp-in-string "[ \t\n\r]" "-" str))
(str (replace-regexp-in-string "[^a-zA-Z-]" "" str)))
str))
This is a variation which will also allow the result to contain numbers:
(defun reasonable-filename (str)
(let* ((str (replace-regexp-in-string "[ \t\n\r]" "-" str))
(str (replace-regexp-in-string "[^a-zA-Z0-9-]" "" str)))
str))
To answer your question about identifying whether a character is an
ASCII letter, the key is that Emacs's characters are really "just"
integers. Wikipedia has some charts[1] that show the numbers associated
with the characters. The letters are conveniently grouped together, so
we can use something like this:
(defun ascii-letter-p (char)
(and (characterp char)
(>= char 65)
(<= char 122)))
(Of course, this only works if it's really a character, as opposed to a
string of length one. If it's a string of length one you could either
"extract" the character with `aref' or use a regular expression
instead.)
Hope that helps.
[1] https://en.wikipedia.org/wiki/ASCII#ASCII_printable_code_chart
--
john
next prev parent reply other threads:[~2014-10-04 2:47 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-04 0:29 How to check whether a character (or one-character string) is a letter? Marcin Borkowski
2014-10-04 1:38 ` Thorsten Jolitz
[not found] ` <CAOj2CQQsnNxtUPzPV8Vw_DgfGFXUUkZExHbArAu_zDjQn-prvw@mail.gmail.com>
2014-10-04 2:47 ` John Mastro [this message]
2014-10-05 0:11 ` Fwd: " Marcin Borkowski
2014-10-04 2:58 ` Eric Abrahamsen
2014-10-04 4:08 ` Yuri Khan
2014-10-05 0:08 ` Marcin Borkowski
2014-10-04 7:29 ` Eli Zaretskii
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