[gambit-list] Type checking

Dear Gambit List,

I have a set of datatypes defined with c-define-type based on the GNU Scientific Library. The Gambit-C manual says "For type checking on the Scheme side..." to use the TAG function of the type definition as in

(c-define-type gsl-matrix* (pointer gsl-matrix "gsl-matrix*"))

What is the best way to use this to define a boolean test (e.g. gsl-matrix*?) for this type? I feel like I must be missing something since the explanation of type checking stops with how to define the TAG and how it's printed in the external representation of an object of that type.

For example: ;;gsl-matrix-initialize returns a pointer ;;to a gsl-matrix (define A (gsl-matrix-initialize)) A #<gsl-matrix* 2 0x38f9e89>

Thanks, Joel