Getting a type of a variable

Getting a type of a variable

[Maciek Godek]

Hello,
I'm looking for an efficient way to check the
type of an SCM variable. I imagine that I
could write something like:
(define (type? x)
  (cond ((integer? x) 'int)
  (cond ((real? x) 'double)
...
)

and then convert guile symbol to C string, but that
would be terribly inefficient. (I could also use an integer
to refer to a type, but there's still this 'cond' clause)

The solution of my dreams is that it would turn out
that there's a function defined in the scm api:
scm_t_bits scm_get_type(SCM *var)
that returns a type tag and that there's a way to decipher
the contents of this return value, and that it is wisely
defined for all builtin types.

(I started to implement such thing by myself as a separate
module, but please inform me if it's already done)

Thanks in advance for help

Re: Getting a type of a variable

[Andy Wingo]

On Fri 18 Jul 2008 23:48, "Maciek Godek" <pstrychuj@gmail.com> writes:

> Hello,
> I'm looking for an efficient way to check the
> type of an SCM variable. I imagine that I
> could write something like:
> (define (type? x)
>   (cond ((integer? x) 'int)
>   (cond ((real? x) 'double)
> ...
> )

(oop goops)'s `class-of'

Andy
-- 
http://wingolog.org/

Re: Getting a type of a variable

[Ludovic Courtès]

Hello,

"Maciek Godek" <pstrychuj@gmail.com> writes:

> The solution of my dreams is that it would turn out
> that there's a function defined in the scm api:
> scm_t_bits scm_get_type(SCM *var)
> that returns a type tag and that there's a way to decipher
> the contents of this return value, and that it is wisely
> defined for all builtin types.

If you are to dive into such low-level things, you could implement in
Scheme type tag "deciphering".  You'd use the `object-address'
procedure, and then re-implement type tag encoding/decoding from
"libguile/tags.h" at the Scheme level.  That'd be an interesting
exercise as the Scheme implementation would be readily understandable
(compared to obscure C macros and informal comments).

Otherwise, Andy's suggestion may be wiser.  ;-)

Thanks,
Ludovic.