feat: explanation as observer too

internal/executer/executer.go

@@ -1,7 +1,6 @@
 package executer
 
 import (
-	"fmt"
 	"log/slog"
 
 	"git.maximhutz.com/max/lambda/internal/config"
@@ -10,28 +9,22 @@ import (
 )
 
 type Executor struct {
-	Config *config.Config
+	Config     *config.Config
+	Expression *lambda.Expression
 	emitter.Emitter
 }
 
-func New(config *config.Config) *Executor {
-	return &Executor{Config: config}
+func New(config *config.Config, expression *lambda.Expression) *Executor {
+	return &Executor{Config: config, Expression: expression}
 }
 
-func (e Executor) Run(expr *lambda.Expression) {
+func (e Executor) Run() {
 	e.Emit("start")
 
-	if e.Config.Explanation {
-		fmt.Println(lambda.Stringify(*expr))
-	}
-
-	for lambda.ReduceOnce(expr) {
+	for lambda.ReduceOnce(e.Expression) {
 		e.Emit("step")
 		if e.Config.Verbose {
-			slog.Info("reduction", "tree", lambda.Stringify(*expr))
-		}
-		if e.Config.Explanation {
-			fmt.Println("    =", lambda.Stringify(*expr))
+			slog.Info("reduction", "tree", lambda.Stringify(*e.Expression))
 		}
 	}
 

internal/explanation/tracker.go

@@ -0,0 +1,28 @@
+package explanation
+
+import (
+	"fmt"
+
+	"git.maximhutz.com/max/lambda/internal/executer"
+	"git.maximhutz.com/max/lambda/pkg/lambda"
+)
+
+type Tracker struct {
+	process *executer.Executor
+}
+
+func Track(process *executer.Executor) *Tracker {
+	tracker := &Tracker{process: process}
+	process.On("start", tracker.Start)
+	process.On("step", tracker.Step)
+
+	return tracker
+}
+
+func (t *Tracker) Start() {
+	fmt.Println(lambda.Stringify(*t.process.Expression))
+}
+
+func (t *Tracker) Step() {
+	fmt.Println("    =", lambda.Stringify(*t.process.Expression))
+}