type checking for arbitrary lisp objects

type checking for arbitrary lisp objects

[Roland Winkler]

The function bbdb-check-type performs a type checking for atomic or
compound lisp objects by comparing these objects against patterns
that use a syntax kind of similar to the :type keyword used by
defcustom (but without the extra keywords such as :tag used by
defcustom).  So a typical pattern is something like the following

   (vector (or string (const nil))
           (repeat string)
           (repeat (vector string (repeat string)
                           string string))
           (repeat (cons symbol string))
           sexp)

I am just wondering: Am I here reinventing the wheel because
something similar has been developed already in some other package?
If not, could this possibly also be useful for other packages (for
example, for defining predicates used by the safe-local-variable
property)?

Roland

Re: type checking for arbitrary lisp objects

[Daniel Colascione]

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On 04/11/2014 12:10 PM, Roland Winkler wrote:
> The function bbdb-check-type performs a type checking for atomic or
> compound lisp objects by comparing these objects against patterns
> that use a syntax kind of similar to the :type keyword used by
> defcustom (but without the extra keywords such as :tag used by
> defcustom).  So a typical pattern is something like the following
> 
>    (vector (or string (const nil))
>            (repeat string)
>            (repeat (vector string (repeat string)
>                            string string))
>            (repeat (cons symbol string))
>            sexp)
> 
> I am just wondering: Am I here reinventing the wheel because
> something similar has been developed already in some other package?
> If not, could this possibly also be useful for other packages (for
> example, for defining predicates used by the safe-local-variable
> property)?

Why not use cl-deftype?


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Re: type checking for arbitrary lisp objects

[Roland Winkler]

On Fri Apr 11 2014 Daniel Colascione wrote:
> Why not use cl-deftype?

...Interesting! - I guess the main difference to what I have in mind
is that cl-deftype appears to require some lisp code for FORMS.
I am thinking about replacing these forms by some more readable
pattern such as the one I included in my first post.  The function
bbdb-check-type then compares an arbitrary lisp object against such
pattern.  I find it more readable and also more flexible to define
patterns instead of hacking actual code.

Re: type checking for arbitrary lisp objects

[Stefan Monnier]

>> Why not use cl-deftype?
> ...Interesting! - I guess the main difference to what I have in mind
> is that cl-deftype appears to require some lisp code for FORMS.
> I am thinking about replacing these forms by some more readable
> pattern such as the one I included in my first post.  The function
> bbdb-check-type then compares an arbitrary lisp object against such
> pattern.  I find it more readable and also more flexible to define
> patterns instead of hacking actual code.

AFAIK cl-deftype is specifically there to define those patterns, so you
can later pass them to cl-check-type.


        Stefan

Re: type checking for arbitrary lisp objects

[Roland Winkler]

On Fri Apr 11 2014 Stefan Monnier wrote:
> AFAIK cl-deftype is specifically there to define those patterns, so you
> can later pass them to cl-check-type.

I begin to understand how this is supposed to work.  Is it also
possible to define more complex types recursively, similar to `list'
and `repeat' used by defcustom's :type keyword?  My complete
knowledge about these cl functions is based on their info page,
which is somewhat brief.

Thanks.

Re: type checking for arbitrary lisp objects

[Stefan Monnier]

> I begin to understand how this is supposed to work.  Is it also
> possible to define more complex types recursively, similar to `list'
> and `repeat' used by defcustom's :type keyword?  My complete
> knowledge about these cl functions is based on their info page,
> which is somewhat brief.

If you do a search for "clhs deftype" on your favorite search engine
you should find the Common Lisp doc for that macro.  The cl-lib version
may not be 100% faithful, but it's usually pretty close,


        Stefan