add: for & if & while support.

CanonSharp.Pascal/SyntaxTree/ForNode.cs

@@ -0,0 +1,20 @@
+using CanonSharp.Pascal.Scanner;
+
+namespace CanonSharp.Pascal.SyntaxTree;
+
+public sealed class ForNode(
+    LexicalToken identifier,
+    SyntaxNodeBase leftCondition,
+    SyntaxNodeBase rightCondition,
+    SyntaxNodeBase statement) : SyntaxNodeBase
+{
+    public override SyntaxNodeType NodeType => SyntaxNodeType.For;
+
+    public LexicalToken Identifier => identifier;
+
+    public SyntaxNodeBase LeftCondition => leftCondition;
+
+    public SyntaxNodeBase RightCondition => rightCondition;
+
+    public SyntaxNodeBase Statement => statement;
+}

CanonSharp.Pascal/SyntaxTree/IfNode.cs

@@ -0,0 +1,26 @@
+namespace CanonSharp.Pascal.SyntaxTree;
+
+public sealed class IfNode : SyntaxNodeBase
+{
+    public override SyntaxNodeType NodeType => SyntaxNodeType.If;
+
+    public SyntaxNodeBase Condition { get; }
+
+    public SyntaxNodeBase Statement { get; }
+
+    public SyntaxNodeBase? ElseStatement { get; }
+
+    public IfNode(SyntaxNodeBase condition, SyntaxNodeBase statement)
+    {
+        Condition = condition;
+        Statement = statement;
+        ElseStatement = null;
+    }
+
+    public IfNode(SyntaxNodeBase condition, SyntaxNodeBase statement, SyntaxNodeBase elseStatement)
+    {
+        Condition = condition;
+        Statement = statement;
+        ElseStatement = elseStatement;
+    }
+}

CanonSharp.Pascal/SyntaxTree/SyntaxNodeBase.cs

@@ -14,6 +14,9 @@ public enum SyntaxNodeType
     Block,
     Constant,
     VariableDeclaration,
+    If,
+    While,
+    For,
     ProgramBody,
     ProgramHead,
     Program

CanonSharp.Pascal/SyntaxTree/WhileNode.cs

@@ -0,0 +1,10 @@
+namespace CanonSharp.Pascal.SyntaxTree;
+
+public sealed class WhileNode(SyntaxNodeBase condition, SyntaxNodeBase statement) : SyntaxNodeBase
+{
+    public override SyntaxNodeType NodeType => SyntaxNodeType.While;
+
+    public SyntaxNodeBase Condition => condition;
+
+    public SyntaxNodeBase Statement => statement;
+}