Fix lexical and dynamic binding

src/lisp.c

@@ -135,20 +135,27 @@ DEFSPECIAL(let, "let", (LispVal * bindings, LispVal *body),
            "(bindings &rest body)", "") {
     CHECK_LISTP(bindings);
     StackFrame *stack_ref = LISP_STACK_REF();
-    LispVal *lexenv = Vlexical_environment;
     DOLIST(binding, bindings) {
-        if (SYMBOLP(binding)) {
-            lexenv = CONS(binding, CONS(Qnil, lexenv));
-        } else if (CONSP(binding) && list_length_eq(binding, 2)) {
-            lexenv = CONS(
-                FIRST(binding),
-                CONS(Feval(SECOND(binding), Vlexical_environment), lexenv));
-        } else {
+        if (CONSP(binding) && list_length_eq(binding, 2)) {
+            if (!SYMBOLP(XCAR(binding))) {
+                // TODO better error
+                abort();
+            }
+            RPLACA(XCDR(binding), Feval(SECOND(binding), Vlexical_environment));
+        } else if (!SYMBOLP(binding)) {
             // TODO better error
             abort();
         }
     }
-    push_dynamic_binding(Qlexical_environment, lexenv);
+    push_copy_lexenv();
+    DOLIST(binding, bindings) {
+        // we already checked that all bindings are well formed
+        if (SYMBOLP(binding)) {
+            new_lexical_variable(binding, Qnil);
+        } else {
+            new_lexical_variable(FIRST(binding), SECOND(binding));
+        }
+    }
     return UNWIND_AND_RETURN(stack_ref, Fprogn(body));
 }