fix: unbound substitutions, explanation tag

cmd/lambda/lambda.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"time"
 
 	"git.maximhutz.com/max/lambda/internal/cli"
 	"git.maximhutz.com/max/lambda/pkg/lambda"
@@ -35,9 +36,21 @@ func main() {
 	cli.HandleError(err)
 	logger.Info("Parsed syntax tree.", "tree", lambda.Stringify(expression))
 
-	for lambda.ReduceOnce(&expression) {
-		logger.Info("Reduction.", "tree", lambda.Stringify(expression))
+	start := time.Now()
+
+	if options.Explanation {
+		fmt.Println(lambda.Stringify(expression))
 	}
 
+	for lambda.ReduceOnce(&expression) {
+		logger.Info("Reduction.", "tree", lambda.Stringify(expression))
+		if options.Explanation {
+			fmt.Println("    =", lambda.Stringify(expression))
+		}
+	}
+
+	elapsed := time.Since(start).Milliseconds()
+
 	fmt.Println(lambda.Stringify(expression))
+	fmt.Fprintln(os.Stderr, "Time Spent:", elapsed, "ms")
 }