gc and cons pairs

object.c

@@ -0,0 +1,39 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "inttypes.h"
+#include "wscm.h"
+
+// cons lists
+O cons(O head, O tail) {
+  I mark = rootmark();
+  addroot(&head);
+  addroot(&tail);
+
+  const Z sz = sizeof(H) + sizeof(C);
+  H *h = alloc(sz);
+  h->size = sz;
+  h->type = OBJ_CONS;
+
+  C *c = (C *)(h + 1);
+  c->head = head;
+  c->tail = tail;
+
+  rootreset(mark);
+  return BOX(h);
+}
+
+C *uncons(O obj) {
+  if (obj == NIL)
+    return NULL;
+  if (IMM(obj)) {
+    fprintf(stderr, "unpair: expected pair, got integer\n");
+    abort();
+  }
+  H *h = UNBOX(obj);
+  if (h->type != OBJ_CONS) {
+    fprintf(stderr, "unpair: expected pair, got type %" PRIdPTR "\n", h->type);
+    abort();
+  }
+  return (C *)(h + 1);
+}