feat: registry, normalorder engine, lambda codec and marshaler

pkg/engine/normalorder/engine.go

@@ -0,0 +1,34 @@
+package normalorder
+
+import (
+	"git.maximhutz.com/max/lambda/pkg/engine"
+	"git.maximhutz.com/max/lambda/pkg/lambda"
+)
+
+type Engine struct {
+	expr lambda.Expression
+}
+
+func (e Engine) Get() (lambda.Expression, error) {
+	return e.expr, nil
+}
+
+func (e Engine) Set(l lambda.Expression) error {
+	e.expr = l
+	return nil
+}
+
+func (e Engine) Step(i int) bool {
+	var reduced bool
+
+	for range i {
+		e.expr, reduced = ReduceOnce(e.expr)
+		if !reduced {
+			return false
+		}
+	}
+
+	return true
+}
+
+var _ engine.Engine[lambda.Expression] = (*Engine)(nil)

pkg/engine/normalorder/reduce_one.go

@@ -0,0 +1,34 @@
+package normalorder
+
+import "git.maximhutz.com/max/lambda/pkg/lambda"
+
+func ReduceOnce(e lambda.Expression) (lambda.Expression, bool) {
+	switch e := e.(type) {
+	case lambda.Abstraction:
+		body, reduced := ReduceOnce(e.Body())
+		if reduced {
+			return lambda.NewAbstraction(e.Parameter(), body), true
+		}
+		return e, false
+
+	case lambda.Application:
+		if fn, fnOk := e.Abstraction().(lambda.Abstraction); fnOk {
+			return fn.Body().Substitute(fn.Parameter(), e.Argument()), true
+		}
+
+		abs, reduced := ReduceOnce(e.Abstraction())
+		if reduced {
+			return lambda.NewApplication(abs, e.Argument()), true
+		}
+
+		arg, reduced := ReduceOnce(e.Argument())
+		if reduced {
+			return lambda.NewApplication(e.Abstraction(), arg), true
+		}
+
+		return e, false
+
+	default:
+		return e, false
+	}
+}