Allowing tree rewrite to remove REM statements and renumber application.

Closes #1.

src/main/java/com/webcodepro/applecommander/util/applesoft/Visitors.java

@@ -3,11 +3,14 @@ package com.webcodepro.applecommander.util.applesoft;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.PrintStream;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Stack;
 import java.util.function.Function;
 
+import com.webcodepro.applecommander.util.applesoft.Token.Type;
+
 /**
  * This class presents all of the common Visitor implementations via builder patterns.
  * The number is currently small enough that all the builders and visitors are defined 
@@ -49,6 +52,11 @@ public class Visitors {
 	public static ByteVisitor byteVisitor(int address) {
 		return new ByteVisitor(address);
 	}
+	
+	/** Rewrite the Program tree with the line number reassignments given. */
+	public static ReassignmentVisitor reassignVisitor(Map<Integer,Integer> reassignments) {
+		return new ReassignmentVisitor(reassignments);
+	}
 
 	private static class PrettyPrintVisitor implements Visitor {
 		private PrintStream printStream;
@@ -268,4 +276,64 @@ public class Visitors {
 			}
 		}
 	}
+
+	/** This is a mildly rewritable Visitor. */
+	private static class ReassignmentVisitor implements Visitor {
+		private Map<Integer,Integer> reassignments;
+		
+		private ReassignmentVisitor(Map<Integer,Integer> reassignments) {
+			this.reassignments = reassignments;
+		}
+		
+		@Override
+		public Program visit(Program program) {
+			Program newProgram = new Program();
+			program.lines.forEach(l -> {
+				Line line = l.accept(this);
+				newProgram.lines.add(line);
+			});
+			return newProgram;
+		}
+		@Override
+		public Line visit(Line line) {
+			Line newLine = new Line(line.lineNumber);
+			line.statements.forEach(s -> {
+				Statement statement = s.accept(this);
+				newLine.statements.add(statement);
+			});
+			return newLine;
+		}
+		/**
+		 * We saw a trigger, reassign any numbers that follow.
+		 * 
+		 * Trigger cases:
+		 * - GOSUB n
+		 * - GOTO n
+		 * - IF ... THEN n
+		 * - LIST n [ ,m ]
+		 * - ON x GOTO n, m, ...
+		 * - ON x GOSUB n, m, ...
+		 * - ONERR GOTO n
+		 * - RUN n
+		 */
+		@Override
+		public Statement visit(Statement statement) {
+			boolean next = false;
+			Statement newStatement = new Statement();
+			for (Token t : statement.tokens) {
+				Token newToken = t;
+				if (next) {
+					if (t.type == Type.NUMBER && reassignments.containsKey(t.number.intValue())) {
+						newToken = Token.number(t.line, reassignments.get(t.number.intValue()).doubleValue());
+					}
+				} else {
+					next = t.keyword == ApplesoftKeyword.GOSUB || t.keyword == ApplesoftKeyword.GOTO 
+						|| t.keyword == ApplesoftKeyword.THEN || t.keyword == ApplesoftKeyword.RUN
+						|| t.keyword == ApplesoftKeyword.LIST;
+				}
+				newStatement.tokens.add(newToken);
+			}
+			return newStatement;
+		}
+	}
 }

src/main/java/io/github/applecommander/bastokenizer/Optimization.java

@@ -1,11 +1,15 @@
 package io.github.applecommander.bastokenizer;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import com.webcodepro.applecommander.util.applesoft.Line;
 import com.webcodepro.applecommander.util.applesoft.Program;
 import com.webcodepro.applecommander.util.applesoft.Statement;
 import com.webcodepro.applecommander.util.applesoft.Token;
 import com.webcodepro.applecommander.util.applesoft.Token.Type;
 import com.webcodepro.applecommander.util.applesoft.Visitor;
+import com.webcodepro.applecommander.util.applesoft.Visitors;
 
 import picocli.CommandLine.ITypeConverter;
 
@@ -51,12 +55,25 @@ public enum Optimization {
 	private static class BaseVisitor implements Visitor {
 		@Override
 		public Program visit(Program program) {
-			Program newProgram = new Program();
+			final Program newProgram = new Program();
+			Map<Integer,Integer> reassignments = new HashMap<>();
 			program.lines.forEach(l -> {
 				Line line = l.accept(this);
-				if (line != null && !line.statements.isEmpty()) newProgram.lines.add(line);
+				boolean lineKept = line != null && !line.statements.isEmpty();
+				if (lineKept) {
+					newProgram.lines.add(line);
+					reassignments.replaceAll((k,v) -> v == null ? l.lineNumber : v);
+				} else {
+					// Make a place-holder for the reassignment; we'll patch it in once we find a line that sticks around.
+					reassignments.put(l.lineNumber, null);
+				}
 			});
-			return newProgram;
+			if (!reassignments.isEmpty()) {
+				// Now, renumber based on our findings!
+				return newProgram.accept(Visitors.reassignVisitor(reassignments));
+			} else {
+				return newProgram;
+			}
 		}
 		@Override
 		public Line visit(Line line) {