diff --git a/internal/registry_new/conversion.go b/internal/registry_new/conversion.go
new file mode 100644
index 0000000..c6e2c5b
--- /dev/null
+++ b/internal/registry_new/conversion.go
@@ -0,0 +1,9 @@
+package registrynew
+
+// Conversion
+type Conversion interface {
+	InRepr() string
+	OutRepr() string
+
+	Run(Expr) (Expr, error)
+}
diff --git a/internal/registry_new/engine.go b/internal/registry_new/engine.go
new file mode 100644
index 0000000..c590d90
--- /dev/null
+++ b/internal/registry_new/engine.go
@@ -0,0 +1,12 @@
+package registrynew
+
+type Process interface {
+	Get() (Expr, error)
+	Step(int) bool
+}
+
+type Engine interface {
+	Load(Expr) Process
+	Name() string
+	InRepr() string
+}
diff --git a/internal/registry_new/expr.go b/internal/registry_new/expr.go
new file mode 100644
index 0000000..29b75b5
--- /dev/null
+++ b/internal/registry_new/expr.go
@@ -0,0 +1,7 @@
+package registrynew
+
+type Expr interface {
+	Repr() string
+
+	Data() any
+}
diff --git a/internal/registry_new/marshaler.go b/internal/registry_new/marshaler.go
new file mode 100644
index 0000000..3913228
--- /dev/null
+++ b/internal/registry_new/marshaler.go
@@ -0,0 +1,5 @@
+package registrynew
+
+type Marshaler interface {
+	InType() string
+}
diff --git a/internal/registry_new/registry.go b/internal/registry_new/registry.go
new file mode 100644
index 0000000..a16a8db
--- /dev/null
+++ b/internal/registry_new/registry.go
@@ -0,0 +1,10 @@
+package registrynew
+
+import "iter"
+
+type Registry interface {
+	ListEngines() iter.Seq[string]
+	GetEngine(name string) (Engine, error)
+
+	ListReprs() iter.Seq[string]
+}
diff --git a/internal/registry_new/repr.go b/internal/registry_new/repr.go
new file mode 100644
index 0000000..d1d8294
--- /dev/null
+++ b/internal/registry_new/repr.go
@@ -0,0 +1,4 @@
+package registrynew
+
+type Repr interface {
+}