AST refactoring

Src/AST/Myc.Ast.Nodes.pas

@@ -20,7 +20,8 @@ type
         function ToString: string;
     end;
 
-    TAstValueKind = (avkUndefined, avkScalar, avkClosure);
+    // Added avkText to represent a string value.
+    TAstValueKind = (avkUndefined, avkScalar, avkClosure, avkText);
 
     // --- Forward Declarations to break cycles ---
     IExecutionScope = interface;
@@ -56,23 +57,21 @@ type
     private
         FKind: TAstValueKind;
         FScalar: TScalar;
-        FClosure: IEvaluatorClosure;
+        FInterface: IInterface;
         function GetKind: TAstValueKind; inline;
-        function GetIsScalar: Boolean; inline;
-        function GetIsClosure: Boolean; inline;
-        function GetIsUndefined: Boolean; inline;
+        function GetIsVoid: Boolean; inline;
     public
         class operator Initialize(out Dest: TAstValue);
-        class function Undefined: TAstValue; static;
+        class function Void: TAstValue; static;
         class function FromScalar(const AValue: TScalar): TAstValue; static;
         class function FromClosure(const AValue: IEvaluatorClosure): TAstValue; static;
+        class function FromText(const AValue: String): TAstValue; static;
         function AsScalar: TScalar;
         function AsClosure: IEvaluatorClosure;
+        function AsText: String;
         function ToString: String;
+        property IsVoid: Boolean read GetIsVoid;
         property Kind: TAstValueKind read GetKind;
-        property IsScalar: Boolean read GetIsScalar;
-        property IsClosure: Boolean read GetIsClosure;
-        property IsUndefined: Boolean read GetIsUndefined;
     end;
 
     IExecutionScope = interface(IInterface)
@@ -198,19 +197,51 @@ type
 
 implementation
 
+uses
+    System.Classes;
+
+type
+    // Private interface to encapsulate a string value for reference counting.
+    IAstTextValue = interface(IInterface)
+        function GetValue: string;
+        property Value: string read GetValue;
+    end;
+
+    // Implementation of the text value interface.
+    TAstTextValue = class(TInterfacedObject, IAstTextValue)
+    private
+        FValue: string;
+        function GetValue: string;
+    public
+        constructor Create(const AValue: string);
+    end;
+
+{ TAstTextValue }
+
+constructor TAstTextValue.Create(const AValue: string);
+begin
+    inherited Create;
+    FValue := AValue;
+end;
+
+function TAstTextValue.GetValue: string;
+begin
+    Result := FValue;
+end;
+
 { TAstValue }
 
 class operator TAstValue.Initialize(out Dest: TAstValue);
 begin
     Dest.FKind := avkUndefined;
-    Dest.FClosure := nil;
+    Dest.FInterface := nil;
 end;
 
 function TAstValue.AsClosure: IEvaluatorClosure;
 begin
     if (FKind <> avkClosure) then
         raise EInvalidCast.Create('Cannot read value as a Closure.');
-    Result := FClosure;
+    Result := IEvaluatorClosure(FInterface);
 end;
 
 function TAstValue.AsScalar: TScalar;
@@ -220,10 +251,17 @@ begin
     Result := FScalar;
 end;
 
+function TAstValue.AsText: String;
+begin
+    if (FKind <> avkText) then
+        raise EInvalidCast.Create('Cannot read value as Text.');
+    Result := IAstTextValue(FInterface).Value;
+end;
+
 class function TAstValue.FromClosure(const AValue: IEvaluatorClosure): TAstValue;
 begin
     Result.FKind := avkClosure;
-    Result.FClosure := AValue;
+    Result.FInterface := AValue;
     Result.FScalar := Default(TScalar);
 end;
 
@@ -231,20 +269,17 @@ class function TAstValue.FromScalar(const AValue: TScalar): TAstValue;
 begin
     Result.FKind := avkScalar;
     Result.FScalar := AValue;
-    Result.FClosure := nil;
+    Result.FInterface := nil;
 end;
 
-function TAstValue.GetIsClosure: Boolean;
+class function TAstValue.FromText(const AValue: String): TAstValue;
 begin
-    Result := FKind = avkClosure;
+    Result.FKind := avkText;
+    Result.FInterface := TAstTextValue.Create(AValue);
+    Result.FScalar := Default(TScalar);
 end;
 
-function TAstValue.GetIsScalar: Boolean;
-begin
-    Result := FKind = avkScalar;
-end;
-
-function TAstValue.GetIsUndefined: Boolean;
+function TAstValue.GetIsVoid: Boolean;
 begin
     Result := FKind = avkUndefined;
 end;
@@ -259,13 +294,14 @@ begin
     case FKind of
         avkScalar: Result := FScalar.ToString;
         avkClosure: Result := '<closure>';
+        avkText: Result := AsText;
         avkUndefined: Result := '<void>';
     else
         Result := '[Unknown AstValue]';
     end;
 end;
 
-class function TAstValue.Undefined: TAstValue;
+class function TAstValue.Void: TAstValue;
 begin
     Result := Default(TAstValue);
 end;