feat: statistics flag, commented some more

internal/engine/engine.go

@@ -0,0 +1,27 @@
+package engine
+
+import (
+	"git.maximhutz.com/max/lambda/internal/config"
+	"git.maximhutz.com/max/lambda/pkg/emitter"
+	"git.maximhutz.com/max/lambda/pkg/lambda"
+)
+
+type Engine struct {
+	Config     *config.Config
+	Expression *lambda.Expression
+	emitter.Emitter
+}
+
+func New(config *config.Config, expression *lambda.Expression) *Engine {
+	return &Engine{Config: config, Expression: expression}
+}
+
+func (e Engine) Run() {
+	e.Emit("start")
+
+	for lambda.ReduceOnce(e.Expression) {
+		e.Emit("step")
+	}
+
+	e.Emit("end")
+}