xo-reader: refactor: + parserstatemachine; use for def_expr

include/xo/reader/parserstatemachine.hpp

@@ -0,0 +1,36 @@
+/* file parserstatemachine.hpp
+ *
+ * author: Roland Conybeare, Aug 2024
+ */
+
+#pragma once
+
+#include "exprstate.hpp"
+
+namespace xo {
+    namespace scm {
+        /** @class parserstatemachine
+         *  @brief public parser state.
+         *
+         *  Schematica parser state; sent to subsidiary single-feature state machines.
+         *  For example entry points for the lambda feature (@ref lambda_xs)
+         *  will accept a non-const parserstatemachine pointer argument
+         **/
+        class parserstatemachine {
+        public:
+            using Expression = xo::ast::Expression;
+
+        public:
+            parserstatemachine(exprstatestack * p_stack,
+                               rp<Expression> * p_emit_expr)
+                : p_stack_{p_stack}, p_emit_expr_{p_emit_expr} {}
+
+        public:
+            exprstatestack * p_stack_;
+            rp<Expression> * p_emit_expr_;
+        };
+    } /*namespace scm*/
+} /*namespace xo*/
+
+
+/* end parserstatemachine.hpp */