pit: Fix evaluator bug

1 files changed, 9 insertions, 7 deletions

diff --git a/pit/src/runtime/symtab.c b/pit/src/runtime/symtab.c
index 5684074..0f46fff 100644
--- a/pit/src/runtime/symtab.c
+++ b/pit/src/runtime/symtab.c
@@ -104,24 +104,26 @@ void pit_symtab_symbol_mark_special_form(pit_runtime *rt, pit_value sym) {
     if (!ent) { pit_error(rt, "bad symbol"); return; }
     ent->is_special_form = true;
 }
-#include <stdio.h>
+void pit_symtab_replace(pit_runtime *rt, pit_value sym, pit_value cell) {
+    /* rebind a symbol without pushing the old binding to the stack */
+    /* this is used in e.g. tail calls, where the old bindings are no longer accessible */
+    pit_symtab_entry *ent = pit_symtab_lookup(rt, sym);
+    if (!ent) { pit_error(rt, "bad symbol"); return; }
+    ent->value = cell;
+}
 void pit_symtab_bind(pit_runtime *rt, pit_value sym, pit_value cell) {
     /* although we cannot set frozen symbols, we can still bind them temporarily - no need to check */
-    fprintf(stderr, "binding "); pit_dump_to_file(rt, stderr, sym, false);
-    fprintf(stderr, " to "); pit_dump_to_file(rt, stderr, cell, false);
-    fprintf(stderr, "\n");
     pit_symtab_entry *ent = pit_symtab_lookup(rt, sym);
     if (!ent) { pit_error(rt, "bad symbol"); return; }
     if (pit_vec_push(pit_value)(rt->saved_bindings, ent->value) < 0) pit_error(rt, "binding stack overflow");
     ent->value = cell;
 }
 pit_value pit_symtab_unbind(pit_runtime *rt, pit_value sym) {
+    /* unbind a symbol! pops a cell from the saved binding stack and resets the symbol's value cell */
+    /* note that we must be careful to unbind symbols in the exact opposite order that we bind them */
     pit_symtab_entry *ent = pit_symtab_lookup(rt, sym);
     if (!ent) { pit_error(rt, "bad symbol"); return PIT_NIL; }
     pit_value old = ent->value;
-    fprintf(stderr, "unbinding "); pit_dump_to_file(rt, stderr, sym, false);
-    fprintf(stderr, " (was "); pit_dump_to_file(rt, stderr, old, false);
-    fprintf(stderr, ")\n");
     if (pit_vec_pop(pit_value)(rt->saved_bindings, &ent->value) < 0) pit_error(rt, "binding stack underflow");
     return old;
 }