Rewrite the stack

src/lisp.c

@@ -19,8 +19,10 @@ static void construct_manual_symbols(void) {
     lisp_gc_register_static_object(Qt);
     Qunbound = Fmake_symbol(LISP_LITSTR("unbound"));
     ((LispSymbol *) Qunbound)->value = Qunbound;
-    ((LispSymbol *) Qunbound)->value = Qunbound;
     lisp_gc_register_static_object(Qunbound);
+    Qlexical_environment = Fmake_symbol(LISP_LITSTR("lexical-environment"));
+    ((LispSymbol *) Qlexical_environment)->value = Qnil;
+    lisp_gc_register_static_object(Qlexical_environment);
 
     Qhash_string = Fmake_symbol(LISP_LITSTR("hash-string"));
     lisp_gc_register_static_object(Qhash_string);
@@ -41,6 +43,7 @@ static void register_manual_symbols(void) {
 
 void lisp_init(void) {
     construct_manual_symbols();
+    Vlexical_environment = Qnil;
     obarray = Fmake_hash_table(Qhash_string, Qstrings_equal);
     lisp_gc_register_static_object(obarray);
 
@@ -63,8 +66,8 @@ void lisp_init(void) {
 }
 
 void lisp_shutdown(void) {
-    lisp_gc_teardown();
     lisp_teardown_stack();
+    lisp_gc_teardown();
 }
 
 static inline LispVal *lookup_variable(LispSymbol *name, LispVal *lexenv) {
@@ -120,7 +123,7 @@ DEFUN(eval, "eval", (LispVal * form, LispVal *lexenv),
 DEFSPECIAL(progn, "progn", (LispVal * forms), "(&rest forms)", "") {
     LispVal *rval = Qnil;
     DOLIST(form, forms) {
-        rval = Feval(form, TOP_LEXENV());
+        rval = Feval(form, Vlexical_environment);
     }
     return rval;
 }
@@ -128,18 +131,20 @@ DEFSPECIAL(progn, "progn", (LispVal * forms), "(&rest forms)", "") {
 DEFSPECIAL(let, "let", (LispVal * bindings, LispVal *body),
            "(bindings &rest body)", "") {
     CHECK_LISTP(bindings);
-    copy_parent_lexenv();
+    LispVal *lexenv = Vlexical_environment;
     DOLIST(binding, bindings) {
         if (SYMBOLP(binding)) {
-            new_lexical_variable(binding, Qnil);
+            lexenv = CONS(binding, CONS(Qnil, lexenv));
         } else if (CONSP(binding) && list_length_eq(binding, 2)) {
-            new_lexical_variable(FIRST(binding),
-                                 Feval(SECOND(binding), TOP_LEXENV()));
+            lexenv = CONS(
+                FIRST(binding),
+                CONS(Feval(SECOND(binding), Vlexical_environment), lexenv));
         } else {
             // TODO better error
             abort();
         }
     }
+    push_dynamic_binding(Qlexical_environment, lexenv);
     return Fprogn(body);
 }