Add 'GLOBAL' keyword #122

Also provides functionality that makes things like overriding the built in
'print' possible. See #67

cheatsheet.md

@@ -167,6 +167,12 @@ auto j; // equiv to var
 var k = 5; // initialized to 5 (integer)
 var l := k; // reference to k
 auto &m = k; // reference to k
+
+GLOBAL g = 5; // creates a global variable. If global already exists, it is not re-added
+GLOBAL g = 2; // global 'g' now equals 2
+
+GLOBAL g2;
+if (g2.is_var_undef()) { g2 = 4; } // only initialize g2 once, if GLOBAL decl hit more than once
 ```
 
 ## Built in Types

include/chaiscript/dispatchkit/dispatchkit.hpp

@@ -487,6 +487,23 @@ namespace chaiscript
           }
         }
 
+        /// Adds a new global (non-const) shared object, between all the threads
+        Boxed_Value add_global_no_throw(const Boxed_Value &obj, const std::string &name)
+        {
+          validate_object_name(name);
+
+          chaiscript::detail::threading::unique_lock<chaiscript::detail::threading::shared_mutex> l(m_global_object_mutex);
+
+          const auto itr = m_state.m_global_objects.find(name);
+          if (itr == m_state.m_global_objects.end())
+          {
+            m_state.m_global_objects.insert(std::make_pair(name, obj));
+            return obj;
+          } else {
+            return itr->second;
+          }
+        }
+
 
         /// Adds a new global (non-const) shared object, between all the threads
         void add_global(const Boxed_Value &obj, const std::string &name)

include/chaiscript/language/chaiscript_common.hpp

@@ -38,7 +38,7 @@ namespace chaiscript
                 Comparison, Addition, Subtraction, Multiplication, Division, Modulus, Array_Call, Dot_Access, Quoted_String, Single_Quoted_String,
                 Lambda, Block, Def, While, If, For, Inline_Array, Inline_Map, Return, File, Prefix, Break, Continue, Map_Pair, Value_Range,
                 Inline_Range, Annotation, Try, Catch, Finally, Method, Attr_Decl, Shift, Equality, Bitwise_And, Bitwise_Xor, Bitwise_Or, 
-                Logical_And, Logical_Or, Reference, Switch, Case, Default, Ternary_Cond, Noop, Class, Binary, Arg
+                Logical_And, Logical_Or, Reference, Switch, Case, Default, Ternary_Cond, Noop, Class, Binary, Arg, Global_Decl
     };
   };
 

include/chaiscript/language/chaiscript_engine.hpp

@@ -346,6 +346,9 @@ namespace chaiscript
       m_engine.add_reserved_word("true");
       m_engine.add_reserved_word("false");
       m_engine.add_reserved_word("class");
+      m_engine.add_reserved_word("attr");
+      m_engine.add_reserved_word("var");
+      m_engine.add_reserved_word("GLOBAL");
       m_engine.add_reserved_word("_");
 
       if (t_lib)

include/chaiscript/language/chaiscript_eval.hpp

@@ -539,6 +539,33 @@ namespace chaiscript
         }
     };
 
+    struct Global_Decl_AST_Node : public AST_Node {
+      public:
+        Global_Decl_AST_Node(std::string t_ast_node_text, Parse_Location t_loc, std::vector<AST_NodePtr> t_children) :
+          AST_Node(std::move(t_ast_node_text), AST_Node_Type::Global_Decl, std::move(t_loc), std::move(t_children)) { }
+        virtual ~Global_Decl_AST_Node() {}
+        virtual Boxed_Value eval_internal(chaiscript::detail::Dispatch_Engine &t_ss) const CHAISCRIPT_OVERRIDE {
+
+          const std::string &idname =
+            [&]()->const std::string &{
+              if (children[0]->identifier == AST_Node_Type::Reference) {
+                return children[0]->children[0]->text;
+              } else {
+                return children[0]->text;
+              }
+            }();
+
+          try {
+            return t_ss.add_global_no_throw(Boxed_Value(), idname);
+          }
+          catch (const exception::reserved_word_error &) {
+            throw exception::eval_error("Reserved word used as global '" + idname + "'");
+          }
+
+        }
+    };
+
+
     struct Var_Decl_AST_Node : public AST_Node {
       public:
         Var_Decl_AST_Node(std::string t_ast_node_text, Parse_Location t_loc, std::vector<AST_NodePtr> t_children) :

include/chaiscript/language/chaiscript_parser.hpp

@@ -323,8 +323,6 @@ namespace chaiscript
         if (is_deep) {
           new_children.assign(std::make_move_iterator(m_match_stack.begin() + static_cast<int>(t_match_start)), 
                               std::make_move_iterator(m_match_stack.end()));
-//          new_children = std::vector<AST_NodePtr>(std::make_move_iterator(m_match_stack.begin() + static_cast<int>(t_match_start)), 
-//                                     std::make_move_iterator(m_match_stack.end()));
           m_match_stack.erase(m_match_stack.begin() + static_cast<int>(t_match_start), m_match_stack.end());
         }
 
@@ -1970,7 +1968,7 @@ namespace chaiscript
           }
 
           build_match<eval::Attr_Decl_AST_Node>(prev_stack_top);
-        } else if (Keyword("auto") || Keyword("var")) {
+        } else if (Keyword("auto") || Keyword("var") ) {
           retval = true;
 
           if (!(Reference() || Id())) {
@@ -1978,6 +1976,14 @@ namespace chaiscript
           }
 
           build_match<eval::Var_Decl_AST_Node>(prev_stack_top);
+        } else if (Keyword("GLOBAL")) {
+          retval = true;
+
+          if (!(Reference() || Id())) {
+            throw exception::eval_error("Incomplete global declaration", File_Position(m_line, m_col), *m_filename);
+          }
+
+          build_match<eval::Global_Decl_AST_Node>(prev_stack_top);
         } else if (Keyword("attr")) {
           retval = true;
 

unittests/global.chai

@@ -0,0 +1,18 @@
+// Test global 
+
+GLOBAL g = 3;
+assert_true(g == 3);
+
+var v := g;
+assert_true(v == 3);
+
+GLOBAL g = 2;
+assert_true(g == 2);
+assert_true(v == 2);
+
+def f() {
+  assert_true(g == 2);
+}
+
+f();
+