Maybe this is the right thing to do?

https://stackoverflow.com/questions/59489221/using-the-gmp-library-with-boehms-garbage-collector

implementations/C/Makefile

@@ -1,5 +1,6 @@
 COPTS=-I/usr/local/include
+STATIC_GCLIB=/usr/local/lib/libgc.a /usr/local/lib/libgmp.a
 
 joy: joy.c
-	cc $(COPTS) joy.c -o joy
+	cc $(COPTS) joy.c $(STATIC_GCLIB) -o joy
 

implementations/C/joy.c

@@ -1,8 +1,46 @@
 #include <gc.h>
 #include <gmp.h>
 
+// Example S-exprs
+// https://www.hboehm.info/gc/04tutorial.pdf
+
+typedef union se
+{
+  struct cons * cp;
+  mpz_t i;
+} sexpr;
+
+struct cons
+{
+  union se head;
+  union se tail;
+};
+
+#define car(s) (s).cp->head
+#define cdr(s) (s).cp->tail
+#define from_i(z) ({sexpr tmp; tmp.i=z; tmp;})
+#define to_i(s) (s).i
+
+sexpr cons(sexpr a, sexpr b) {
+    sexpr tmp = {GC_MALLOC(sizeof(struct cons))};
+    car(tmp) = a; cdr(tmp) = b;
+    return (tmp);
+};
+
+void* reallocate_function (void *ptr, size_t old_size, size_t new_size) {
+    return GC_realloc(ptr, new_size);
+}
+void deallocate_function (void *ptr, size_t size) {
+    GC_free(ptr);
+}
 int main(void)
 {
+    mp_set_memory_functions(
+        &GC_malloc,
+        &reallocate_function,
+        &deallocate_function
+        );
     return 0;
+    //return to_i(car(cons(from_i(0),from_i(1))));
 }