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 -- Joel J. Adamson Biostatistician Pediatric Psychopharmacology Research Unit Massachusetts General Hospital Boston, MA 02114 (617) 643-1432 (303) 880-3109 The information transmitted in this electronic communication is intended only for the person or entity to whom it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of or taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you received this information in error, please contact the Compliance HelpLine at 800-856-1983 and properly dispose of this information.