How to concatenate a backslash to a string

How to concatenate a backslash to a string

[Mirko]

Hello group.

When in *scratch* I try
(concat "\\" "%")
I get "\\%"

But what I really want is to get "\%".   (I am trying to TeXify some
text and convert %->\%, $->\$, etc).

If I try (concat "\" "%") I get a syntax error because the \ is
escaping the ".

Many thanks,

Mirko

Re: How to concatenate a backslash to a string

[David Kastrup]

"Mirko" <mvukovic@nycap.rr.com> writes:

> Hello group.
>
> When in *scratch* I try
> (concat "\\" "%")
> I get "\\%"

Sure.

> But what I really want is to get "\%".

There is no such thing.  This is illegal string syntax.

> (I am trying to TeXify some text and convert %->\%, $->\$, etc).

Have you tried what happens if you do
(insert "\\%")
in a buffer?

> If I try (concat "\" "%") I get a syntax error because the \ is
> escaping the ".

Sure.  But you don't expect when typing
(insert "x")
that the quote characters end up in your buffer, as they are merely
part of the string syntax.  So why do you expect that the doubled
backslashes, which are merely part of the string syntax, end up in the
buffer?

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

Re: How to concatenate a backslash to a string

[Robert Thorpe]

Mirko wrote:
> Hello group.
>
> When in *scratch* I try
> (concat "\\" "%")
> I get "\\%"
>
> But what I really want is to get "\%".   (I am trying to TeXify some
> text and convert %->\%, $->\$, etc).
>
> If I try (concat "\" "%") I get a syntax error because the \ is
> escaping the ".

In Lisp print and read are exact opposites.  What print emits will
produce the same data when read by read.  So, if read needs something
to be quoted then print must quote it.

If you do (concat "\\" %") the resulting string is \% if you do (princ
(concat "\\" "%")) you will see this.

When you just evaluate this though you effectively get (print (concat
"\\" "%")) and print quotes the \ so read can understand it later.

Re: How to concatenate a backslash to a string

[Perry Smith]

On Nov 27, 2006, at 10:37 AM, Mirko wrote:

> Hello group.
>
> When in *scratch* I try
> (concat "\\" "%")
> I get "\\%"
>
> But what I really want is to get "\%".   (I am trying to TeXify some
> text and convert %->\%, $->\$, etc).
>
> If I try (concat "\" "%") I get a syntax error because the \ is
> escaping the ".

You may be getting what you want.  Notice that "\\" in the scratch  
buffer gives you back "\\" (I'm assuming you are hitting control-J to  
eval and print the line.

I don't think you can get any string in the scratch buffer to print  
like you want it.  It will always have an even number of \'s when  
printed.

Perry Smith ( pedz@easesoftware.com )
Ease Software, Inc. ( http://www.easesoftware.com )

Low cost SATA Disk Systems for IBMs p5, pSeries, and RS/6000 AIX systems

Re: How to concatenate a backslash to a string

[Mirko]

Perry Smith wrote:
> On Nov 27, 2006, at 10:37 AM, Mirko wrote:
>
> > Hello group.
> >
> > When in *scratch* I try
> > (concat "\\" "%")
> > I get "\\%"
> >
> > But what I really want is to get "\%".   (I am trying to TeXify some
> > text and convert %->\%, $->\$, etc).
> >
> > If I try (concat "\" "%") I get a syntax error because the \ is
> > escaping the ".
>
> You may be getting what you want.  Notice that "\\" in the scratch
> buffer gives you back "\\" (I'm assuming you are hitting control-J to
> eval and print the line.
>
> I don't think you can get any string in the scratch buffer to print
> like you want it.  It will always have an even number of \'s when
> printed.
>
> Perry Smith ( pedz@easesoftware.com )
> Ease Software, Inc. ( http://www.easesoftware.com )
>
> Low cost SATA Disk Systems for IBMs p5, pSeries, and RS/6000 AIX systems

Thanks to all three of you.  Indeed, I was confused by the output in
the *scratch* buffer.  Once I tested the ouput of my commands in an
actual buffer, I was got the expected behavior: a single backslash
followd by whatever symbol I wanted.

Thanks again

Mirko

PS  Another newbie question is brewing, but I am still trying to figure
it out :-)

Re: How to concatenate a backslash to a string

[Kevin Rodgers]

David Kastrup wrote:
> "Mirko" <mvukovic@nycap.rr.com> writes:
>> But what I really want is to get "\%".
> 
> There is no such thing.  This is illegal string syntax.

<nit>
Not really: (equal "\%" "%") ==> t
</nit>

-- 
Kevin