feat: engine -> process, engine is now a factory for a proces

pkg/engine/normalorder/engine.go

@@ -5,20 +5,20 @@ import (
 	"git.maximhutz.com/max/lambda/pkg/lambda"
 )
 
-type Engine struct {
+type Process struct {
 	expr lambda.Expression
 }
 
-func (e Engine) Get() (lambda.Expression, error) {
+func (e Process) Get() (lambda.Expression, error) {
 	return e.expr, nil
 }
 
-func (e *Engine) Set(l lambda.Expression) error {
+func (e *Process) Set(l lambda.Expression) error {
 	e.expr = l
 	return nil
 }
 
-func (e *Engine) Step(i int) bool {
+func (e *Process) Step(i int) bool {
 	for range i {
 		next, reduced := ReduceOnce(e.expr)
 		if !reduced {
@@ -31,4 +31,12 @@ func (e *Engine) Step(i int) bool {
 	return true
 }
 
+type Engine struct {
+}
+
+func (e Engine) Load() engine.Process[lambda.Expression] {
+	return &Process{}
+}
+
+var _ engine.Process[lambda.Expression] = (*Process)(nil)
 var _ engine.Engine[lambda.Expression] = (*Engine)(nil)