diff --git a/ownlang-desktop/src/main/java/com/annimon/ownlang/Main.java b/ownlang-desktop/src/main/java/com/annimon/ownlang/Main.java
index d654436..dd02879 100644
--- a/ownlang-desktop/src/main/java/com/annimon/ownlang/Main.java
+++ b/ownlang-desktop/src/main/java/com/annimon/ownlang/Main.java
@@ -4,7 +4,9 @@ import com.annimon.ownlang.exceptions.OwnLangParserException;
 import com.annimon.ownlang.exceptions.StoppedException;
 import com.annimon.ownlang.parser.*;
 import com.annimon.ownlang.parser.ast.Statement;
+import com.annimon.ownlang.parser.error.ParseErrorsFormatterStage;
 import com.annimon.ownlang.parser.linters.LinterStage;
+import com.annimon.ownlang.parser.optimization.OptimizationStage;
 import com.annimon.ownlang.stages.*;
 import com.annimon.ownlang.utils.Repl;
 import com.annimon.ownlang.utils.Sandbox;
@@ -142,13 +144,13 @@ public final class Main {
         final var scopedStages = new ScopedStageFactory(measurement::start, measurement::stop);
 
         final var stagesData = new StagesDataMap();
-        stagesData.put(OptimizationStage.TAG_OPTIMIZATION_SUMMARY, options.showAst);
         stagesData.put(SourceLoaderStage.TAG_SOURCE, input);
         try {
             scopedStages.create("Lexer", new LexerStage())
                     .then(scopedStages.create("Parser", new ParserStage()))
                     .thenConditional(options.optimizationLevel > 0,
-                            scopedStages.create("Optimization", new OptimizationStage(options.optimizationLevel)))
+                            scopedStages.create("Optimization",
+                                    new OptimizationStage(options.optimizationLevel, options.showAst)))
                     .thenConditional(options.lintMode,
                             scopedStages.create("Linter", new LinterStage()))
                     .then(scopedStages.create("Function adding", new FunctionAddingStage()))
@@ -173,8 +175,9 @@ public final class Main {
             if (options.showAst) {
                 Statement program = stagesData.get(ParserStage.TAG_PROGRAM);
                 System.out.println(program);
+                System.out.println(stagesData.getOrDefault(OptimizationStage.TAG_OPTIMIZATION_SUMMARY, ""));
             }
-            if (!options.showMeasurements) {
+            if (options.showMeasurements) {
                 System.out.println("======================");
                 System.out.println(measurement.summary(TimeUnit.MILLISECONDS, true));
             }
diff --git a/ownlang-parser/src/main/java/com/annimon/ownlang/parser/Optimizer.java b/ownlang-parser/src/main/java/com/annimon/ownlang/parser/Optimizer.java
deleted file mode 100644
index a4f2ff6..0000000
--- a/ownlang-parser/src/main/java/com/annimon/ownlang/parser/Optimizer.java
+++ /dev/null
@@ -1,49 +0,0 @@
-package com.annimon.ownlang.parser;
-
-import com.annimon.ownlang.Console;
-import com.annimon.ownlang.parser.ast.Node;
-import com.annimon.ownlang.parser.ast.Statement;
-import com.annimon.ownlang.parser.optimization.ConstantFolding;
-import com.annimon.ownlang.parser.optimization.ConstantPropagation;
-import com.annimon.ownlang.parser.optimization.DeadCodeElimination;
-import com.annimon.ownlang.parser.optimization.ExpressionSimplification;
-import com.annimon.ownlang.parser.optimization.InstructionCombining;
-import com.annimon.ownlang.parser.optimization.Optimizable;
-import com.annimon.ownlang.parser.optimization.SummaryOptimization;
-
-public final class Optimizer {
-
-    private Optimizer() { }
-
-    public static Statement optimize(Statement statement, int level, boolean showSummary) {
-        if (level == 0) return statement;
-
-        final Optimizable optimization = new SummaryOptimization(new Optimizable[] {
-            new ConstantFolding(),
-            new ConstantPropagation(),
-            new DeadCodeElimination(),
-            new ExpressionSimplification(),
-            new InstructionCombining()
-        });
-
-        Node result = statement;
-        if (level >= 9) {
-            int iteration = 0, lastModifications = 0;
-            do {
-                lastModifications = optimization.optimizationsCount();
-                result = optimization.optimize(result);
-                iteration++;
-            } while (lastModifications != optimization.optimizationsCount());
-            if (showSummary)
-                Console.print("Performs " + iteration + " optimization iterations");
-        } else {
-            for (int i = 0; i < level; i++) {
-                result = optimization.optimize(result);
-            }
-        }
-        if (showSummary) {
-            Console.println(optimization.summaryInfo());
-        }
-        return (Statement) result;
-    }
-}
diff --git a/ownlang-parser/src/main/java/com/annimon/ownlang/parser/optimization/OptimizationStage.java b/ownlang-parser/src/main/java/com/annimon/ownlang/parser/optimization/OptimizationStage.java
new file mode 100644
index 0000000..ee7811c
--- /dev/null
+++ b/ownlang-parser/src/main/java/com/annimon/ownlang/parser/optimization/OptimizationStage.java
@@ -0,0 +1,56 @@
+package com.annimon.ownlang.parser.optimization;
+
+import com.annimon.ownlang.parser.ast.Node;
+import com.annimon.ownlang.parser.ast.Statement;
+import com.annimon.ownlang.stages.Stage;
+import com.annimon.ownlang.stages.StagesData;
+
+public class OptimizationStage implements Stage<Statement, Statement> {
+
+    public static final String TAG_OPTIMIZATION_SUMMARY = "optimizationSummary";
+
+    private final int level;
+    private final boolean summary;
+    private final Optimizable optimization;
+
+    public OptimizationStage(int level) {
+        this(level, false);
+    }
+
+    public OptimizationStage(int level, boolean summary) {
+        this.level = level;
+        this.summary = summary;
+        optimization = new SummaryOptimization(new Optimizable[] {
+                new ConstantFolding(),
+                new ConstantPropagation(),
+                new DeadCodeElimination(),
+                new ExpressionSimplification(),
+                new InstructionCombining()
+        });
+    }
+
+    @Override
+    public Statement perform(StagesData stagesData, Statement input) {
+        if (level == 0) return input;
+
+        Node result = input;
+        final int maxIterations = level >= 9 ? Integer.MAX_VALUE : level;
+        int lastModifications;
+        int iteration = 0;
+        do {
+            lastModifications = optimization.optimizationsCount();
+            result = optimization.optimize(result);
+            iteration++;
+        } while (lastModifications != optimization.optimizationsCount() && iteration < maxIterations);
+
+        if (this.summary) {
+            stagesData.put(TAG_OPTIMIZATION_SUMMARY, """
+                Performed %d optimization iterations
+                %s
+                """.formatted(iteration, optimization.summaryInfo())
+            );
+        }
+
+        return (Statement) result;
+    }
+}
diff --git a/ownlang-parser/src/main/java/com/annimon/ownlang/stages/OptimizationStage.java b/ownlang-parser/src/main/java/com/annimon/ownlang/stages/OptimizationStage.java
deleted file mode 100644
index dfbe00f..0000000
--- a/ownlang-parser/src/main/java/com/annimon/ownlang/stages/OptimizationStage.java
+++ /dev/null
@@ -1,16 +0,0 @@
-package com.annimon.ownlang.stages;
-
-import com.annimon.ownlang.parser.Optimizer;
-import com.annimon.ownlang.parser.ast.Statement;
-
-public record OptimizationStage(int level)
-        implements Stage<Statement, Statement> {
-
-    public static final String TAG_OPTIMIZATION_SUMMARY = "optimizationSummary";
-
-    @Override
-    public Statement perform(StagesData stagesData, Statement input) {
-        boolean showSummary = stagesData.getOrDefault(TAG_OPTIMIZATION_SUMMARY, false);
-        return Optimizer.optimize(input, level, showSummary);
-    }
-}