From 633d4a4d3bc84d824de8cdb303baf5313bdf52b6 Mon Sep 17 00:00:00 2001
From: Max <git@maximhutz.me>
Date: Sun, 28 Dec 2025 02:19:48 -0500
Subject: [PATCH] fix: no stringify in hot loop

---
 Makefile                 |  3 +++
 cmd/lambda/lambda.go     | 12 +++++++++---
 pkg/lambda/substitute.go | 14 ++++++--------
 samples/church.txt       |  7 +++++++
 4 files changed, 25 insertions(+), 11 deletions(-)
 create mode 100644 samples/church.txt

diff --git a/Makefile b/Makefile
index d7db258..895db60 100644
--- a/Makefile
+++ b/Makefile
@@ -13,6 +13,9 @@ thunk: it
 saccharine: it
 	@ ./lambda.exe - < ./samples/saccharine.txt
 
+church: it
+	@ ./lambda.exe - < ./samples/church.txt
+
 prof:
 	@ go tool pprof -top profile/cpu.prof
 
diff --git a/cmd/lambda/lambda.go b/cmd/lambda/lambda.go
index b593434..be7ced2 100644
--- a/cmd/lambda/lambda.go
+++ b/cmd/lambda/lambda.go
@@ -41,10 +41,14 @@ func main() {
 	// Turn tokens into syntax tree.
 	expression, err := saccharine.Parse(tokens)
 	cli.HandleError(err)
-	logger.Info("parsed syntax tree", "tree", saccharine.Stringify(expression))
+	if options.Verbose {
+		logger.Info("parsed syntax tree", "tree", saccharine.Stringify(expression))
+	}
 
 	compiled := convert.SaccharineToLambda(expression)
-	logger.Info("compiled lambda expression", "tree", lambda.Stringify(compiled))
+	if options.Verbose {
+		logger.Info("compiled lambda expression", "tree", lambda.Stringify(compiled))
+	}
 
 	// Reduce expression.
 	start := time.Now()
@@ -56,7 +60,9 @@ func main() {
 	steps := 0
 
 	for lambda.ReduceOnce(&compiled) {
-		logger.Info("reduction", "tree", lambda.Stringify(compiled))
+		if options.Verbose {
+			logger.Info("reduction", "tree", lambda.Stringify(compiled))
+		}
 		if options.Explanation {
 			fmt.Println("    =", lambda.Stringify(compiled))
 		}
diff --git a/pkg/lambda/substitute.go b/pkg/lambda/substitute.go
index 96d4ec2..8798165 100644
--- a/pkg/lambda/substitute.go
+++ b/pkg/lambda/substitute.go
@@ -11,16 +11,14 @@ func Substitute(e *Expression, target string, replacement Expression) {
 			return
 		}
 
-		if !IsFreeVariable(typed.Parameter, replacement) {
-			Substitute(&typed.Body, target, replacement)
-			return
+		if IsFreeVariable(typed.Parameter, replacement) {
+			replacementFreeVars := GetFreeVariables(replacement)
+			used := GetFreeVariables(typed.Body)
+			used.Merge(replacementFreeVars)
+			freshVar := GenerateFreshName(used)
+			Rename(typed, typed.Parameter, freshVar)
 		}
 
-		replacementFreeVars := GetFreeVariables(replacement)
-		used := GetFreeVariables(typed.Body)
-		used.Merge(replacementFreeVars)
-		freshVar := GenerateFreshName(used)
-		Rename(typed, typed.Parameter, freshVar)
 		Substitute(&typed.Body, target, replacement)
 	case *Application:
 		Substitute(&typed.Abstraction, target, replacement)
diff --git a/samples/church.txt b/samples/church.txt
new file mode 100644
index 0000000..571d394
--- /dev/null
+++ b/samples/church.txt
@@ -0,0 +1,7 @@
+0 := \f.\x.x
+inc n := \f x.(f (n f x))
+exp n m := (m n)
+
+N := (inc (inc (inc (inc (inc 0)))))
+
+(exp N N)