xo-reader: feat: + var lookup in envframestack, psm

include/xo/reader/envframestack.hpp

@@ -13,12 +13,21 @@ namespace xo {
          *  @brief A stack of envframe objects
          **/
         class envframestack {
+        public:
+            using Variable = xo::ast::Variable;
+
         public:
             envframestack() {}
 
             bool empty() const { return stack_.empty(); }
             std::size_t size() const { return stack_.size(); }
 
+            /** lookup variable in environment stack.
+             *  Visit frames in fifo order,  report first match;
+             *  nullptr if no matches.
+             **/
+            rp<Variable> lookup(const std::string & x) const;
+
             envframe & top_envframe();
             void push_envframe(envframe x);
             void pop_envframe();

include/xo/reader/parserstatemachine.hpp

@@ -20,6 +20,7 @@ namespace xo {
         class parserstatemachine {
         public:
             using Expression = xo::ast::Expression;
+            using Variable = xo::ast::Variable;
 
         public:
             parserstatemachine(exprstatestack * p_stack,
@@ -33,6 +34,14 @@ namespace xo {
             exprstate & top_exprstate();
             void push_exprstate(std::unique_ptr<exprstate> x);
 
+            /** lookup variable name in lexical context represented by
+             *  this psm.  nullptr if not found
+             **/
+            rp<Variable> lookup_var(const std::string & x) const;
+
+            void push_envframe(envframe x);
+            void pop_envframe();
+
         public:
             /** stack of incomplete parser work.
              *  generally speaking, push when to start new work for nested content;

src/reader/envframestack.cpp

@@ -6,6 +6,8 @@
 #include "envframestack.hpp"
 
 namespace xo {
+    using xo::ast::Variable;
+
     namespace scm {
         envframe &
         envframestack::top_envframe() {
@@ -50,6 +52,20 @@ namespace xo {
             }
         }
 
+        rp<Variable>
+        envframestack::lookup(const std::string & x) const {
+            for (std::size_t i = 0, z = this->size(); i < z; ++i) {
+                const auto & frame = (*this)[i];
+
+                auto retval = frame.lookup(x);
+
+                if (retval)
+                    return retval;
+            }
+
+            return nullptr;
+        }
+
         void
         envframestack::print(std::ostream & os) const {
             os << "<envframestack"

src/reader/parserstatemachine.cpp

@@ -7,7 +7,14 @@
 #include "exprstatestack.hpp"
 
 namespace xo {
+    using xo::ast::Variable;
+
     namespace scm {
+        rp<Variable>
+        parserstatemachine::lookup_var(const std::string & x) const {
+            return p_env_stack_->lookup(x);
+        }
+
         std::unique_ptr<exprstate>
         parserstatemachine::pop_exprstate() {
             return p_stack_->pop_exprstate();
@@ -22,6 +29,16 @@ namespace xo {
         parserstatemachine::push_exprstate(std::unique_ptr<exprstate> x) {
             p_stack_->push_exprstate(std::move(x));
         }
+
+        void
+        parserstatemachine::push_envframe(envframe x) {
+            p_env_stack_->push_envframe(std::move(x));
+        }
+
+        void
+        parserstatemachine::pop_envframe() {
+            p_env_stack_->pop_envframe();
+        }
     } /*namespace scm*/
 } /*namespace xo*/