Interpolated string support.

language/interpreter.cc

@@ -20,6 +20,7 @@ struct Eval
             case Identifier:   return eval_identifier(ast, env);
             case Number:       return eval_number(ast, env);
             case Boolean:      return eval_bool(ast, env);
+            case InterpolatedString: return eval_interpolated_string(ast, env);
         }
 
         if (ast.is_token) {
@@ -174,6 +175,15 @@ private:
         return Value(ast.token == "true");
     };
 
+    static Value eval_interpolated_string(const Ast& ast, Env& env) {
+        string s;
+        for (auto node: ast.nodes) {
+            const auto& val = eval(*node, env);
+            s += val.str();
+        }
+        return Value(s);
+    };
+
     static Value dereference_identirier(Env& env, const string& var) {
         if (!env.has(var)) {
             string msg = "undefined variable '" + var + "'...";

language/interpreter.hpp

@@ -61,6 +61,19 @@ struct Value
         throw std::runtime_error("type error.");
     }
 
+    std::string str() const {
+        switch (type) {
+            case Undefined: return "undefined";
+            case Bool:      return to_bool() ? "true" : "false";
+            case Long:      return std::to_string(to_long()); break;
+            case String:    return to_string();
+            //case Function:  return "[function]";
+            //case Array:     return "[array]";
+            default: throw std::logic_error("invalid internal condition.");
+        }
+        // NOTREACHED
+    }
+
     std::ostream& out(std::ostream& os) const {
         switch (type) {
             case Undefined: os << "undefined"; break;
@@ -181,7 +194,7 @@ struct Env
         auto func_pretty_print = Value::FunctionValue {
             { "arg" },
             [](Env& env) {
-                std::cout << env.get("arg") << std::endl;
+                std::cout << env.get("arg").str() << std::endl;
                 return Value();
             }
         };

language/parser.cc

@@ -20,7 +20,7 @@ static auto g_grammar = R"(
     PRIMARY             <-  CONDITION (CONDITION_OPERATOR CONDITION)?
     CONDITION           <-  TERM (TERM_OPERATOR TERM)*
     TERM                <-  FACTOR (FACTOR_OPERATOR FACTOR)*
-    FACTOR              <-  WHILE / IF / FUNCTION / FUNCTION_CALL / NUMBER / BOOLEAN / STRING / IDENTIFIER / '(' _ EXPRESSION ')' _
+    FACTOR              <-  WHILE / IF / FUNCTION / FUNCTION_CALL / NUMBER / BOOLEAN / STRING / INTERPOLATED_STRING / IDENTIFIER / '(' _ EXPRESSION ')' _
 
     BLOCK               <-  '{' _ STATEMENTS '}' _
 
@@ -33,6 +33,9 @@ static auto g_grammar = R"(
     BOOLEAN             <-  < ('true' / 'false') > _
     STRING              <-  ['] < (!['] .)* > ['] _
 
+    INTERPOLATED_STRING   <-  '"' ('{' _ EXPRESSION '}' / INTERPOLATED_CONTENT)* '"' _
+    INTERPOLATED_CONTENT  <-  (!["{] .) (!["{] .)*
+
     ~_                  <-  (Space / EndOfLine / Comment)*
     Space               <-  ' ' / '\t'
     EndOfLine           <-  '\r\n' / '\n' / '\r'
@@ -76,6 +79,8 @@ peglib::peg& get_parser()
             .ast_token("BOOLEAN", Boolean)
             .ast_token("STRING")
             .ast_token("IDENTIFIER", Identifier)
+            .ast_node("INTERPOLATED_STRING", InterpolatedString)
+            .ast_token("INTERPOLATED_CONTENT")
             .ast_end();
     }
 

language/parser.hpp

@@ -3,7 +3,8 @@
 enum AstType
 {
    Statements, While, If, FunctionCall, Assignment, Condition, BinExpresion,
-   Identifier, Number, Boolean, Function
+   Identifier, InterpolatedString,
+   Number, Boolean, Function
 };
 
 peglib::peg& get_parser();