[ELISP] How do you turn an array of chars into a string?

[ELISP] How do you turn an array of chars into a string?

[Joseph Brenner]

The elisp manual has this example, using "kbd" to convert a (relatively)
readable string into the "internal Emacs key representation":

     (global-set-key (kbd "C-x C-\\") 'next-line)

     (global-set-key [?\C-x ?\C-\\] 'next-line)

What's the inverse of kbd?  What if you want to convert an array-of-chars
into a string?

Things like this seem to work, but only for very simple chars:

  (mapconcat 'string [?c ?a ?t] "")  ;; => "cat"

Motivation: see the first FIXME in footnote.el, on footnote-prefix.

Re: [ELISP] How do you turn an array of chars into a string?

[Pascal J. Bourguignon]

Joseph Brenner <doom@kzsu.stanford.edu> writes:

> The elisp manual has this example, using "kbd" to convert a (relatively)
> readable string into the "internal Emacs key representation":
>
>      (global-set-key (kbd "C-x C-\\") 'next-line)
>
>      (global-set-key [?\C-x ?\C-\\] 'next-line)
>
> What's the inverse of kbd?  

> What if you want to convert an array-of-chars
> into a string?

These are two radically different things.   

The inverse of kbd doesn't convert an array of characters into a
string, it would produce a string containing a text describing in a
human readable form the keychoard sequence.

So what do you really want?



To convert a vector of characters to a string you could use:

(require 'cl) ; all the good stuff is always in there!

(coerce [?c ?a ?t] 'string) --> "cat"

(concatenate 'string  "A " [?c ?a ?t] '(?  ?e ?a ?t ?s) " a mouse.")
--> "A cat eats a mouse."



To convert a vector of key chords into a human readable description of
it, I don't know.  But the command where-is seems to be knowing how to
do it, so let's read the source of where-is!  Here, we find a:
(mapconcat 'key-description keys ", ") therefore key-description might
be the right function.  Read the documentation.  Yes!  Notice how it
says nothing about converting vectors to string!!!

(key-description (kbd "C-x C-\\"))
 -->  "C-x C-\\"

(key-description (kbd "C-M-A-s-Z C-u 123 H-S-A-é")) 
 --> "A-C-M-s-z C-u 1 2 3 A-H-S-é"

Looks good...


> Things like this seem to work, but only for very simple chars:
>
>   (mapconcat 'string [?c ?a ?t] "")  ;; => "cat"

What is a non-simple character???


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/

Re: [ELISP] How do you turn an array of chars into a string?

[Joseph Brenner]

pjb@informatimago.com (Pascal J. Bourguignon) writes:

> Joseph Brenner <doom@kzsu.stanford.edu> writes:
>
>> The elisp manual has this example, using "kbd" to convert a (relatively)
>> readable string into the "internal Emacs key representation":
>>
>>      (global-set-key (kbd "C-x C-\\") 'next-line)
>>
>>      (global-set-key [?\C-x ?\C-\\] 'next-line)
>>
>> What's the inverse of kbd?
>
>> What if you want to convert an array-of-chars
>> into a string?
>
> These are two radically different things.
>
> The inverse of kbd doesn't convert an array of characters into a
> string, it would produce a string containing a text describing in a
> human readable form the keychoard sequence.

Which is indeed, a kind of string, and from context, I would hope it's
clear that that's the kind of string I was talking about.

> To convert a vector of characters to a string you could use:
>
> (require 'cl) ; all the good stuff is always in there!
>
> (coerce [?c ?a ?t] 'string) --> "cat"
>
> (concatenate 'string  "A " [?c ?a ?t] '(?  ?e ?a ?t ?s) " a mouse.")
> --> "A cat eats a mouse."

Yes, looks good, but then I'd figured out ways to do that sort of job...

>> Things like this seem to work, but only for very simple chars:
>>
>>   (mapconcat 'string [?c ?a ?t] "")  ;; => "cat"
>
> What is a non-simple character???

Well, for example, it doesn't work for:

  (control ?c)

But then it does work for:

  ?\C-c

SO it could be I was wrong.

> To convert a vector of key chords into a human readable description of
> it, I don't know.  But the command where-is seems to be knowing how to
> do it, so let's read the source of where-is!  Here, we find a:
> (mapconcat 'key-description keys ", ") therefore key-description might
> be the right function.  Read the documentation.  Yes!  Notice how it
> says nothing about converting vectors to string!!!
>
> (key-description (kbd "C-x C-\\"))
>  -->  "C-x C-\\"
>
> (key-description (kbd "C-M-A-s-Z C-u 123 H-S-A-é"))
>  --> "A-C-M-s-z C-u 1 2 3 A-H-S-é"
>
> Looks good...

Yes, thanks much.  That does indeed look like the solution.

Re: [ELISP] How do you turn an array of chars into a string?

[Stefan Monnier]

> The elisp manual has this example, using "kbd" to convert a (relatively)
> readable string into the "internal Emacs key representation":

>      (global-set-key (kbd "C-x C-\\") 'next-line)
>      (global-set-key [?\C-x ?\C-\\] 'next-line)

> What's the inverse of kbd?

key-description

> What if you want to convert an array-of-chars into a string?

A string *is* an array of chars.  If you want to convert a vector
(i.e. one of those arrays that contains arbitrary Lisp values) to
a string, you can use `concat': (concat (vector ?a ?b ?c)) => "abc".


        Stefan

Re: [ELISP] How do you turn an array of chars into a string?

[Pascal J. Bourguignon]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> The elisp manual has this example, using "kbd" to convert a (relatively)
>> readable string into the "internal Emacs key representation":
>
>>      (global-set-key (kbd "C-x C-\\") 'next-line)
>>      (global-set-key [?\C-x ?\C-\\] 'next-line)
>
>> What's the inverse of kbd?
>
> key-description
>
>> What if you want to convert an array-of-chars into a string?
>
> A string *is* an array of chars.  

Not in scheme or emacs lisp.  (vectorp "abc") --> nil


> If you want to convert a vector
> (i.e. one of those arrays that contains arbitrary Lisp values) to
> a string, you can use `concat': (concat (vector ?a ?b ?c)) => "abc".
>
>
>         Stefan

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/

Re: [ELISP] How do you turn an array of chars into a string?

[Johan Bockgård]

pjb@informatimago.com (Pascal J. Bourguignon) writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>> A string *is* an array of chars.
>
> Not in scheme or emacs lisp.  (vectorp "abc") --> nil

(arrayp "abc")  => t

Re: [ELISP] How do you turn an array of chars into a string?

[Pascal J. Bourguignon]

Johan Bockgård <bojohan+news@gnu.org> writes:

> pjb@informatimago.com (Pascal J. Bourguignon) writes:
>
>> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>
>>> A string *is* an array of chars.
>>
>> Not in scheme or emacs lisp.  (vectorp "abc") --> nil
>
> (arrayp "abc")  => t

Ah, right, in emacs array is a supertype of string and vector.

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/

Re: [ELISP] How do you turn an array of chars into a string?

[Stefan Monnier]

>> A string *is* an array of chars.  
> Not in scheme or emacs lisp.  (vectorp "abc") --> nil

(arrayp "abc") => t

Hence my subsequent:

>> If you want to convert a vector
>> (i.e. one of those arrays that contains arbitrary Lisp values) to


        Stefan

Re: [ELISP] How do you turn an array of chars into a string?

[Joseph Brenner]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> What if you want to convert an array-of-chars into a string?
>
> A string *is* an array of chars.

Yes, I've heard that, but:

  (let ((mah-array  [?c ?a ?t])
        (mah-string "cat"))
        (equal mah-array mah-string))  ;; ==> nil

  (let ((mah-array  [?c ?a ?t])
        (mah-string "cat"))
        (string= mah-array mah-string))
   ;; Lisp error: (wrong-type-argument stringp [99 97 116])

Though on the other hand:

  (equal
    (aref [?c ?a ?t] 2)
    (aref "cat" 2))      ;; ==> t

In any case, it doesn't exactly make sense to me to just say
that "a string is an array of chars".

I suppose you might say "a string is an array of chars, with a type
of 'string'".

Re: [ELISP] How do you turn an array of chars into a string?

[Stefan Monnier]

>>> What if you want to convert an array-of-chars into a string?
>> A string *is* an array of chars.
[...]
> In any case, it doesn't exactly make sense to me to just say
> that "a string is an array of chars".

Then I guess a better way to say it is:

a string is one of the various kinds of arrays supported by Elisp
(other types are vectors, char-tables, and bool-vectors).


        Stefan