From 7b9c4a3ac265026d98624ac614eead866a190042 Mon Sep 17 00:00:00 2001
From: LLLL Colonq <llll@colonq>
Date: Mon, 10 Aug 2026 21:49:57 -0400
Subject: pit: VM-style evaluation

---
 pit/include/lcq/pit/runtime.h      | 11 ++++++-----
 pit/include/lcq/pit/runtime/eval.h |  3 ++-
 pit/include/lcq/pit/vec.h          |  2 +-
 3 files changed, 9 insertions(+), 7 deletions(-)

(limited to 'pit/include')

diff --git a/pit/include/lcq/pit/runtime.h b/pit/include/lcq/pit/runtime.h
index a55c2d2..075d94c 100644
--- a/pit/include/lcq/pit/runtime.h
+++ b/pit/include/lcq/pit/runtime.h
@@ -31,12 +31,13 @@ PIT_DECLARE_HASHTABLE(pit_ref, pit_annotation)
 void pit_annotation_set(struct pit_runtime *rt, pit_ref ref, pit_annotation annotation);
 pit_annotation *pit_annotation_get(struct pit_runtime *rt, pit_ref ref);
 
-/* entry in the backtrace */
 typedef struct {
-    pit_value val;
+    pit_value tag; /* (possibly nil) identifier for this frame for error messages */
     pit_annotation ann;
-} pit_backtrace_entry;
-PIT_DECLARE_VEC(pit_backtrace_entry)
+    pit_value bound; /* list of bound names */
+    pit_value code; /* list of vm expressions */
+} pit_callstack_entry;
+PIT_DECLARE_VEC(pit_callstack_entry)
 
 /* entries on a stack used when traversing trees of values */
 typedef struct {
@@ -70,7 +71,7 @@ typedef struct pit_runtime {
     pit_vec(pit_value) *expr_stack; /* stack of subexpressions to evaluate during evaluation */
     pit_vec(pit_value) *result_stack; /* stack of intermediate values during evaluation */
     pit_vec(pit_traversal_entry) *traversal; /* intermediate stack used during tree traversal */
-    pit_vec(pit_backtrace_entry) *backtrace; /* stack of enclosing function calls */
+    pit_vec(pit_callstack_entry) *callstack; /* stack of enclosing function calls */
     /* bookkeeping */
     /* "frozen" values offsets: values before these offsets are immutable, and we can reset here later */
     i64 frozen_values, frozen_symtab;
diff --git a/pit/include/lcq/pit/runtime/eval.h b/pit/include/lcq/pit/runtime/eval.h
index 3dc9e3c..41ec046 100644
--- a/pit/include/lcq/pit/runtime/eval.h
+++ b/pit/include/lcq/pit/runtime/eval.h
@@ -3,6 +3,7 @@
 
 #include <lcq/pit/runtime.h>
 
-pit_value pit_eval(pit_runtime *rt, pit_value e);
+pit_value pit_vm_compile(pit_runtime *rt, pit_value top);
+pit_value pit_vm_eval(pit_runtime *rt, pit_value v);
 
 #endif
diff --git a/pit/include/lcq/pit/vec.h b/pit/include/lcq/pit/vec.h
index b60140f..e4f918c 100644
--- a/pit/include/lcq/pit/vec.h
+++ b/pit/include/lcq/pit/vec.h
@@ -45,7 +45,7 @@
     static __attribute__ ((unused)) i64 pit_vec_pop(ty)(pit_vec(ty) *s, ty *v) { \
         i64 idx = (s->next - 1); \
         if (s->next == 0 || idx + 1 > s->capacity) return -1; \
-        *v = s->data[idx]; \
+        if (v) *v = s->data[idx]; \
         return --s->next; \
     }
 
-- 
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