pit: Add comments

1 files changed, 8 insertions, 3 deletions

diff --git a/pit/src/runtime/eval.c b/pit/src/runtime/eval.c
index f62f4e8..eba9715 100644
--- a/pit/src/runtime/eval.c
+++ b/pit/src/runtime/eval.c
@@ -1,6 +1,7 @@
 #include <lcq/pit/runtime/eval.h>
 
-/* add a new stack frame to the vm (with a tag and callsite annotation) */
+/* add a new code frame to the vm (with a tag and callsite annotation) */
+/* bound is a list of symbols to be unbound when this frame ends */
 static void vm_push_code_func(pit_runtime *rt, pit_value code, pit_value tag, pit_annotation ann, pit_value bound) {
     pit_callstack_entry ent;
     ent.tag = tag;
@@ -12,7 +13,7 @@ static void vm_push_code_func(pit_runtime *rt, pit_value code, pit_value tag, pi
     }
 }
 
-/* add a new stack frame to the vm (with no annotation) */
+/* add a new code frame to the vm (with no annotation) */
 static void vm_push_code(pit_runtime *rt, pit_value code, pit_value bound) {
     pit_annotation ann;
     ann.line = -1;
@@ -20,12 +21,14 @@ static void vm_push_code(pit_runtime *rt, pit_value code, pit_value bound) {
     vm_push_code_func(rt, code, PIT_NIL, ann, bound);
 }
 
+/* push a value to the result stack */
 static void vm_push(pit_runtime *rt, pit_value v) {
     if (pit_vec_push(pit_value)(rt->result_stack, v) < 0) {
         pit_error(rt, "vm stack overflow");
     }
 }
 
+/* pop a value from the result stack */
 static pit_value vm_pop(pit_runtime *rt) {
     pit_value ret = PIT_NIL;
     if (pit_vec_pop(pit_value)(rt->result_stack, &ret) < 0) {
@@ -46,6 +49,7 @@ static pit_value vm_bind_or_replace(pit_runtime *rt, pit_value nm, pit_value cel
     return bound;
 }
 
+/* bind variables and push code for a call to the given lisp closure */
 static void vm_call_lisp(pit_runtime *rt, pit_value tag, pit_value closure, pit_value args, pit_value bound) {
     pit_value env = pit_value_array_get(rt, closure, 0);
     pit_value anames = pit_value_array_get(rt, closure, 1);
@@ -78,6 +82,7 @@ static void vm_call_lisp(pit_runtime *rt, pit_value tag, pit_value closure, pit_
     vm_push_code_func(rt, body, tag, ann, bound);
 }
 
+/* call the function f - this could be a native function or a lisp closure */
 static bool vm_call(pit_runtime *rt, pit_value f, pit_value args, pit_value bound) {
     char buf[256] = {0};
     if (pit_value_is_symbol(rt, f)) f = pit_symtab_fget(rt, f);
@@ -147,7 +152,7 @@ static pit_value vm_erase_empty(pit_runtime *rt, bool unbind) {
 /* run one instruction of the VM */
 bool pit_vm_run_one(pit_runtime *rt) {
     vm_erase_empty(rt, true);
-    if (rt->callstack->next < 1) return false;
+    if (rt->callstack->next < 1 || rt->error != PIT_NIL) return false;
     pit_callstack_entry *ent = pit_vec_get(pit_callstack_entry)(rt->callstack, rt->callstack->next - 1);
     if (ent == NULL) { pit_error(rt, "malformed call stack"); return false; }
     pit_value ins = pit_value_cons_car(rt, ent->code);