From 94ed7ececc7a2979133853e1e541b7f3382b8ae6 Mon Sep 17 00:00:00 2001
From: Max Kaufmann <max.kaufmann@gmail.com>
Date: Tue, 2 Aug 2011 22:38:03 -0700
Subject: [PATCH] else statements

---
 Lang/Block.cs             | 20 +++++++++++++++++++-
 Lang/InstructionParser.cs |  6 ++++++
 Main.cs                   |  5 +++++
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/Lang/Block.cs b/Lang/Block.cs
index fbb7927..b92d070 100644
--- a/Lang/Block.cs
+++ b/Lang/Block.cs
@@ -32,14 +32,32 @@ public Block(List<Instruction> buffer) {
 	public class IfBlock : Block {
 		public BranchInstruction branch;
 		public int branchIndex;
+		public JumpInstruction elseJump = null;
 		
 		public IfBlock(Expression condition, List<Instruction> buffer) : base(buffer) {
 			branchIndex = buffer.Count;
 			branch = new BranchInstruction(condition, branchIndex+1, -1);
+			buffer.Add(branch);
 		}
 		
-		override public void End() {
+		public bool ElseIf(Expression condition) {
+			return false;
+		}
+		
+		public bool Else() {
+			if (elseJump != null) { return false; }
+			elseJump = new JumpInstruction(-1);
+			buffer.Add(elseJump);
 			branch.indexFalse = buffer.Count;
+			return true;
+		}
+		
+		override public void End() {
+			if (elseJump != null) {
+				elseJump.index = buffer.Count;
+			} else {
+				branch.indexFalse = buffer.Count;
+			}
 		}
 		
 		// todo add elseif, else
diff --git a/Lang/InstructionParser.cs b/Lang/InstructionParser.cs
index f1ef2da..eb3fe81 100644
--- a/Lang/InstructionParser.cs
+++ b/Lang/InstructionParser.cs
@@ -97,6 +97,12 @@ State Idle(Token t) {
 						if (mBlock.Count == 0) { return null; }
 						mBlock.Pop().End();
 						return Idle;
+					case "else":
+						if (mBlock.Count == 0) { return null; }
+						var block = mBlock.Peek() as IfBlock;
+						if (block == null) { return null; }
+						if (!block.Else()) { return null; }
+						return Idle;
 					default: break;
 				}
 			}
diff --git a/Main.cs b/Main.cs
index 8c62eae..6968009 100644
--- a/Main.cs
+++ b/Main.cs
@@ -41,6 +41,11 @@ turn left
 					move backward 5
 					stop stroke
 				end
+				if 0
+					move forward 100
+				else
+					move backward 100
+				end
 			");
 			var interpreter = new Interpreter(program);
 			while(interpreter.ExecuteNextInstruction()) {}