separate eval into eval and apply and do gc (oops)

eval.c

@@ -171,6 +171,26 @@ V setupenv(O *env) {
   *env = cons(mkprim("if", prim_if), *env);
 }
 
+O apply(O fn, O args, O env) {
+  I k = kind(fn);
+  switch (k) {
+  case KIND_PRIM: {
+    P *p = (P *)UNTAG(fn);
+    return p->fn(args, env);
+  }
+  case KIND_CLOS: {
+    H *h = UNBOX(fn);
+    L *l = (L *)(h + 1);
+    args = evallist(args, env);
+    O nenv = bind(l->args, args, l->env);
+    return eval(l->body, nenv);
+  }
+  default:
+    fprintf(stderr, "tried to call non-function value\n");
+    abort();
+  }
+}
+
 O eval(O obj, O env) {
   I k = kind(obj);
 
@@ -194,23 +214,7 @@ O eval(O obj, O env) {
   O fn = eval(c->car, env);
   addroot(&fn);
 
-  I fk = kind(fn);
-  O res = NIL;
-
-  if (fk == KIND_PRIM) {
-    P *p = (P *)UNTAG(fn);
-    res = p->fn(c->cdr, env);
-  } else if (fk == KIND_CLOS) {
-    H *h = UNBOX(fn);
-    L *l = (L *)(h + 1);
-    O args = evallist(c->cdr, env);
-    O nenv = bind(l->args, args, l->env);
-    res = eval(l->body, nenv);
-  } else {
-    fprintf(stderr, "tried to call non-function value\n");
-    abort();
-  }
-
+  O res = apply(fn, c->cdr, env);
   rootreset(mark);
   return res;
 }