feat: meaningful comments for internal packages

internal/engine/engine.go

@@ -1,3 +1,5 @@
+// Package "engine" provides an extensible interface for users to interfact with
+// lambda calculus.
 package engine
 
 import (
@@ -6,16 +8,19 @@ import (
 	"git.maximhutz.com/max/lambda/pkg/lambda"
 )
 
+// A process for reducing one lambda expression.
 type Engine struct {
 	Config     *config.Config
 	Expression *lambda.Expression
 	emitter.Emitter
 }
 
+// Create a new engine, given an unreduced lambda expression.
 func New(config *config.Config, expression *lambda.Expression) *Engine {
 	return &Engine{Config: config, Expression: expression}
 }
 
+// Begin the reduction process.
 func (e Engine) Run() {
 	e.Emit("start")