diff --git a/cmd/lambda/lambda.go b/cmd/lambda/lambda.go
index 999e722..843897d 100644
--- a/cmd/lambda/lambda.go
+++ b/cmd/lambda/lambda.go
@@ -34,7 +34,7 @@ func main() {
 	logger.Info("compiled λ expression", "tree", compiled.String())
 
 	// Create reducer with the compiled expression.
-	reducer := lambda.NewNormalOrderReducer(compiled)
+	reducer := lambda.NewNormalOrderReducer(&compiled)
 
 	// If the user selected to track CPU performance, attach a profiler.
 	if options.Profile != "" {
diff --git a/cmd/lambda/lambda_test.go b/cmd/lambda/lambda_test.go
index 73bdb85..8f671d9 100644
--- a/cmd/lambda/lambda_test.go
+++ b/cmd/lambda/lambda_test.go
@@ -30,7 +30,7 @@ func runSample(samplePath string) (string, error) {
 	compiled := convert.SaccharineToLambda(ast)
 
 	// Create and run the reducer.
-	reducer := lambda.NewNormalOrderReducer(compiled)
+	reducer := lambda.NewNormalOrderReducer(&compiled)
 	reducer.Reduce()
 
 	return reducer.Expression().String() + "\n", nil
diff --git a/internal/plugins/performance.go b/internal/plugins/performance.go
index 08cc46b..857eca7 100644
--- a/internal/plugins/performance.go
+++ b/internal/plugins/performance.go
@@ -1,4 +1,4 @@
-// Package "performance" provides a tracker to observe CPU performance during
+// Package "performance" provides a tracker to observer CPU performance during
 // execution.
 package plugins
 
@@ -19,10 +19,10 @@ type Performance struct {
 }
 
 // Create a performance tracker that outputs a profile to "file".
-func NewPerformance(file string, r reducer.Reducer) *Performance {
+func NewPerformance(file string, process reducer.Reducer) *Performance {
 	plugin := &Performance{File: file}
-	r.On(reducer.StartEvent, plugin.Start)
-	r.On(reducer.StopEvent, plugin.Stop)
+	process.On(reducer.StartEvent, plugin.Start)
+	process.On(reducer.StopEvent, plugin.Stop)
 
 	return plugin
 }
diff --git a/pkg/lambda/reducer.go b/pkg/lambda/reducer.go
index 4117096..b4df0e6 100644
--- a/pkg/lambda/reducer.go
+++ b/pkg/lambda/reducer.go
@@ -10,11 +10,11 @@ import (
 // for lambda calculus expressions.
 type NormalOrderReducer struct {
 	emitter.BaseEmitter[reducer.Event]
-	expression Expression
+	expression *Expression
 }
 
 // NewNormalOrderReducer creates a new normal order reducer.
-func NewNormalOrderReducer(expression Expression) *NormalOrderReducer {
+func NewNormalOrderReducer(expression *Expression) *NormalOrderReducer {
 	return &NormalOrderReducer{
 		BaseEmitter: *emitter.New[reducer.Event](),
 		expression:  expression,
@@ -23,7 +23,7 @@ func NewNormalOrderReducer(expression Expression) *NormalOrderReducer {
 
 // Expression returns the current expression state.
 func (r *NormalOrderReducer) Expression() expr.Expression {
-	return r.expression
+	return *r.expression
 }
 
 func isViable(e *Expression) (*Abstraction, Expression, bool) {
@@ -42,7 +42,7 @@ func isViable(e *Expression) (*Abstraction, Expression, bool) {
 // The expression must be a lambda.Expression; other types are returned unchanged.
 func (r *NormalOrderReducer) Reduce() {
 	r.Emit(reducer.StartEvent)
-	it := NewIterator(&r.expression)
+	it := NewIterator(r.expression)
 
 	for !it.Done() {
 		if fn, arg, ok := isViable(it.Current()); !ok {