Re: What is the type of user input?

[Kevin Rodgers <ihs_4664@yahoo.com>]

Hattuari wrote:
 > The following code demonstrates the problem I'm having:
 > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 > ;; create a property list and use it to map long strings
 > ;; to short strings
 > (setq paste-gl-type-map ())
 >
 > (setq paste-gl-type-map (plist-put paste-gl-type-map 'GLbyte     'b))
 > (setq paste-gl-type-map (plist-put paste-gl-type-map 'GLshort    's))
 > (setq paste-gl-type-map (plist-put paste-gl-type-map 'GLint      'i))
 > ;;...
 >
 > (plist-get paste-gl-type-map 'GLbyte) ;; test function call
 >
 >
 > (defun paste-gl-array(gl-type gl-components gl-vector)
 >   "Map OpenGL types to corresponding sufixes.(GL\'type\' )"
 >   (interactive "sType: \nnNumber 1 to 4: \nsVector: ")
 >   (message " gl-type=%s, gl-components=%d, gl-vector=%s , suffix=%s"
 >            gl-type gl-components gl-vector
 >            (plist-get paste-gl-type-map gl-type))
 >
 >   )
 > ;; end of application code
 > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 >
 > When I use the code by first `M-x eval-buffer' and then `M-x
 > paste-gl-array<RET>GLbyte<RET>4<RET>v<RET>', the result is a message
 > displayed in the echo area as follows:
 >
 > gl-type=GLbyte, gl-components=4, gl-vector=v , suffix=nil
 >
 > Notice that gl-type is displayed with the value I entered in the 
minibuffer
 > when it is passed to the first %s in the message string.  It seems not to
 > be treated as a string when passed to plist-get, hence the 'suffix=nil'.

gl-type is a string.  Since the paste-gl-type-map property list is keyed
by symbols, plist-get returns nil.  The %s message specifier can be
applied to any Lisp object, and symbols and strings are formatted the
same.

The solution is to either (1) read gl-type with the %S code or (2) call
plist-get with (intern gl-type).

 > OTOH, when I evaluate this expression in an emacs-lisp buffer
 > (paste-gl-array 'GLbyte 4 'v), I see the following in the echo area:
 >
 > gl-type=GLbyte, gl-components=4, gl-vector=v , suffix=b
 >
 > That is the desired result.  Why is this not the result of calling the
 > function as an interactive command as described above?
 >
 > I will continue to look for an answer in the documentation, but any help
 > from someone who knows the answer would be appreciated.

It's not that hard to find:

`C-h f message' has a link to the doc string for `format', which has a
link to the doc string for `princ' in its description of %s:

,----[ C-h f princ RET ]
| princ is a built-in function.
| (princ OBJECT &optional PRINTCHARFUN)
|
| Output the printed representation of OBJECT, any Lisp object.
| No quoting characters are used; no delimiters are printed around
| the contents of strings.
|
| OBJECT is any of the Lisp data types: a number, a string, a symbol,
| a list, a buffer, a window, a frame, etc.
|
| A printed representation of an object is text which describes that object.
...`----

-- 
Kevin Rodgers