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Re: (read (current-buffer)) returns an integer in a buffer full of text?


From: Robert Thorpe
Subject: Re: (read (current-buffer)) returns an integer in a buffer full of text?
Date: 29 Nov 2006 06:17:44 -0800
User-agent: G2/1.0

Sebastian Tennant wrote:
> Quoth "Robert Thorpe" <address@hidden>:
> > Kevin Rodgers wrote:
> >> Robert Thorpe wrote:
> >> > Sebastian Tennant wrote:
> >> >> Hi everyone,
> >> >>
> >> >> If I execute the following code in *scratch* there's no problem:
> >> >>
> >> >>   (with-temp-buffer
> >> >>     (insert "hello")
> >> >>     (backward-word)
> >> >>     (read (current-buffer)))
> >> >>   => hello
> >> >
> >> > The function with-temp-buffer creates a temp buffer for the duration of
> >> > it's body.  It does _not_ select that buffer as the current buffer.
> >>
> >> Why would that matter?  The (read (current-buffer)) form is evaluated
> >> while the temp buffer is current.  Nothing depends on the temp buffer
> >> still being current after that.
> >
> > You're right, my last sentence is 100% wrong.  With-temp-buffer does
> > set the temp buffer to be the current buffer.
> >
> > I have no idea why this code doesn't work, it works for me under
> > similar conditions.
> > (The only mistake is that (backward-word) should be (backward-word 1))
>
> My error was in the location of point.  If two words are separated by
> a space, and point at the beginning of the second word,
> '(backward-word 2)' is required to move point to the beginning of the
> first word.
>
> However, why does this happen:
>
>  (with-temp-buffer
>    (insert "586114704")
>    (backward-word)
>    (read (current-buffer)))
>
>  => 49243792
>
> Is there an integer limit relating to symbols somehow?

The function "read" will read whatever type it finds.  It will treat
586114704 as an integer.

Try the following:-
Type 586114704 into scratch and do C-x C-e straight afterwards.
The echo area will display 49243792.  This is because there is a limit
on integers in Emacs, they are 26-bits long.  This allows you to
represent -67108865 to 67108864 I think.

Emacs doesn't warn you when you exceed the limit unfortunately.

Generally if you want to do numerical things with Lisp you should use
another lisp such as Common Lisp.



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