Much more progress, still doesn't compile.

src/c/payloads/exception.c

@@ -0,0 +1,13 @@
+
+
+#import "memory/pointer.h"
+#import "memory/pso.h"
+#import "payloads/exception.h"
+
+/**
+ * @param p a pointer to an object.
+ * @return true if that object is an exception, else false.
+ */
+bool exceptionp( struct pso_pointer p) {
+	return (get_tag_value( p) == EXCEPTIONTV);
+}