bug#1939: suggestion: adding read-line function to elisp

bug#1939: suggestion: adding read-line function to elisp

[xah lee]

summary:
i'd like to have a  read-line function in elisp, that will read a  
given file and return a list of lines.

The reason is that in almost all modern scripting langs (php, perl,  
python, ruby), there's such a function, so that users can get a list  
of lines of a file in about single line of code. Getting lines as  
list is a very frequent need.

elisp is very suitable for tasks of text processing. So, having such  
a convenience function seems appropriate.

Here's a implementation:

(defun read-lines (file)
   "Return a list of lines in FILE."
   (with-temp-buffer
     (insert-file-contents file)
     (split-string
      (buffer-substring-no-properties 1 (point-max)) "\n" t)
     )
   )

Thanks.

The thought came from a recent newsgroup discussion in comp.lang.lisp
http://groups.google.com/group/comp.lang.lisp/browse_frm/thread/ 
761fe827c8c9ea5e/

Here's a short article for some context:

• A Ruby Illustration of Lisp Problems
   http://xahlee.org/UnixResource_dir/writ/lisp_problems_by_ruby.html

   Xah
∑ http://xahlee.org/

☄

bug#1939: suggestion: adding read-line function to elisp

[Juanma Barranquero]

On Sat, Jan 17, 2009 at 19:13, xah lee <xah@xahlee.org> wrote:

> Getting lines as list is a very frequent need.
>
> elisp is very suitable for tasks of text processing. So, having such a
> convenience function seems appropriate.

Getting lines as list is much less frequent in elisp. The reason is
that is much more flexible (and faster) to manipulate text in a buffer
than as a collection of strings.

So in most cases, using `with-temp-buffer' (as in your read-lines
function) is the Right Thing To Do.

    Juanma

Re: bug#1939: suggestion: adding read-line function to elisp

[Ted Zlatanov]

On Sun, 18 Jan 2009 06:48:10 +0100 Juanma Barranquero <lekktu@gmail.com> wrote: 

JB> On Sat, Jan 17, 2009 at 19:13, xah lee <xah@xahlee.org> wrote:
>> Getting lines as list is a very frequent need.
>> 
>> elisp is very suitable for tasks of text processing. So, having such a
>> convenience function seems appropriate.

JB> Getting lines as list is much less frequent in elisp. The reason is
JB> that is much more flexible (and faster) to manipulate text in a buffer
JB> than as a collection of strings.

JB> So in most cases, using `with-temp-buffer' (as in your read-lines
JB> function) is the Right Thing To Do.

OTOH, it would be nice to have a way to call a lambda for every line in
a file (`mapfile' essentially) without using a buffer.  The function
would get the line and the line number as parameters.  That would let
Emacs Lisp do some processing of large files without running out of
memory.

Ted