Re: [Axiom-developer] lispdoc

[Kai Kaminski]

On May 16, 2007, at 11:20 AM, Martin Rubey wrote:

> Ralf Hemmecke <address@hidden> writes:
>
> > see <http://planet.lisp.org>
> >
> > I think that won't help me much. But could someone tell me about a  
> > few
> > conventions used in naming identifiers.
A quick overview of the common conventions (and some not so common  
ones) can be found at http://www.cliki.net/Naming%20conventions.

> > I already know that |blah| keeps blah from being capitalized, but  
> > are the bars
> > part of the identifier?
>
> no.
>
> > When do people use identifiers that are surrounded by *, for example
> > *default-pathname-defaults*.
>
> *this-is-a-special-variable*
>
> The stars are only a convention, as you noticed already.
>
> A special variable is dynamically scoped - as opposed to the usual  
> lexical
> scoping in lisp.  It is introduced via (defvar *this-is-a-special- 
> variable*)
Or (defparameter *foo* ...). There is a subtle difference, which you  
probably don't care for, unless you develop your Lisp in an  
interactive way, which is somewhat difficult with the Axiom sources.

> Think of a special variable as a global variable.
>
> > What about a colon in front of an identifier? For example,
> > (array-element-type (make-array 10 :element-type 'character))
>
> As far as I know this is also a convention, namely for keyword  
> arguments.
This isn't quite correct. A symbol that starts with a colon is always  
interned in the KEYWORD package, rather than the current package.  
Keyword symbols are used for keyword arguments in functions:

(defun foo (bar &key baz (bam 3))
  ...)

(foo 3 :bam 7 :baz 9)

You couldn't write (foo 3 bam 7 baz 9) instead, hence it is not a  
convention in this case.

Keyword symbols are also often used (this is by convention) for  
things like

(defun find-extremum (list max-or-min)
  ...)

(find-extremum '(1 2 3 4 5) :max)

Finally keyword symbols are often used in DSLs, like this example  
from cl-who (http://weitz.de/cl-who/):

(with-html-output (*http-stream*)
  (:html
    (:head (:title "My Homepage"))
    (:body (:h1 "hello world"))))

Kai