feat: new engine format

pkg/engine/engine.go

@@ -1,11 +1,12 @@
+// Package engine defines a general process of reducing a lambda calculus
+// expression.
 package engine
 
-type Engine[T any] interface {
-	Load() Process[T]
-}
-
+// A Process handles the reduction of a
 type Process[T any] interface {
 	Get() (T, error)
-	Set(T) error
 	Step(int) bool
 }
+
+// An Engine is an object that handles
+type Engine[T any] = func(T) (Process[T], error)