refact: 将编译中各个阶段接口化 (#35)

Reviewed-on: PostGuard/Canon#35

Canon.Core/SyntaxNodes/NonTerminatedSyntaxNode.cs

@@ -21,12 +21,14 @@ public abstract class NonTerminatedSyntaxNode : SyntaxNodeBase, IEnumerable<Synt
             {
                 yield return child;
             }
-
-            NonTerminatedSyntaxNode nonTerminatedNode = child.Convert<NonTerminatedSyntaxNode>();
-
-            foreach (SyntaxNodeBase node in nonTerminatedNode)
+            else
             {
-                yield return node;
+                NonTerminatedSyntaxNode nonTerminatedNode = child.Convert<NonTerminatedSyntaxNode>();
+
+                foreach (SyntaxNodeBase node in nonTerminatedNode)
+                {
+                    yield return node;
+                }
             }
         }
     }

Canon.Core/SyntaxNodes/ProgramStruct.cs

@@ -1,4 +1,5 @@
-using Canon.Core.Enums;
+using Canon.Core.CodeGenerators;
+using Canon.Core.Enums;
 
 namespace Canon.Core.SyntaxNodes;
 
@@ -20,4 +21,9 @@ public class ProgramStruct : NonTerminatedSyntaxNode
     {
         return new ProgramStruct { Children = children };
     }
+
+    public override void GenerateCCode(CCodeBuilder builder)
+    {
+        builder.AddString("#include <PascalCoreLib.h>");
+    }
 }

Canon.Core/SyntaxNodes/SyntaxNodeBase.cs

@@ -1,9 +1,11 @@
-using Canon.Core.Enums;
+using Canon.Core.Abstractions;
+using Canon.Core.CodeGenerators;
+using Canon.Core.Enums;
 using Canon.Core.LexicalParser;
 
 namespace Canon.Core.SyntaxNodes;
 
-public abstract class SyntaxNodeBase
+public abstract class SyntaxNodeBase : ICCodeGenerator
 {
     public abstract bool IsTerminated { get; }
 
@@ -19,6 +21,14 @@ public abstract class SyntaxNodeBase
         return result;
     }
 
+    /// <summary>
+    /// 语法树节点基类对于生成C代码的默认实现
+    /// </summary>
+    public virtual void GenerateCCode(CCodeBuilder builder)
+    {
+
+    }
+
     public static SyntaxNodeBase Create(SemanticToken token)
     {
         return new TerminatedSyntaxNode { Token = token };