schema: add TypedPrototype

Moving from bindnode, and adding a Type method for consistency with
TypedNode.

Fixes #181.

node/bindnode/api.go

@@ -8,8 +8,8 @@ import (
 	"github.com/ipld/go-ipld-prime/schema"
 )
 
-// Prototype implements a TypedPrototype given a Go pointer type and an IPLD
-// schema type. Note that the result is also an ipld.NodePrototype.
+// Prototype implements a schema.TypedPrototype given a Go pointer type and an
+// IPLD schema type. Note that the result is also an ipld.NodePrototype.
 //
 // If both the Go type and schema type are supplied, it is assumed that they are
 // compatible with one another.
@@ -23,7 +23,7 @@ import (
 // from it, so its underlying value will typically be nil. For example:
 //
 //     proto := bindnode.Prototype((*goType)(nil), schemaType)
-func Prototype(ptrType interface{}, schemaType schema.Type) TypedPrototype {
+func Prototype(ptrType interface{}, schemaType schema.Type) schema.TypedPrototype {
 	if ptrType == nil && schemaType == nil {
 		panic("either ptrType or schemaType must not be nil")
 	}

node/bindnode/node.go

@@ -12,9 +12,9 @@ import (
 // Assert that we implement all the interfaces as expected.
 // Grouped by the interfaces to implement, roughly.
 var (
-	_ ipld.NodePrototype = (*_prototype)(nil)
-	_ TypedPrototype     = (*_prototype)(nil)
-	_ ipld.NodePrototype = (*_prototypeRepr)(nil)
+	_ ipld.NodePrototype    = (*_prototype)(nil)
+	_ schema.TypedPrototype = (*_prototype)(nil)
+	_ ipld.NodePrototype    = (*_prototypeRepr)(nil)
 
 	_ ipld.Node        = (*_node)(nil)
 	_ schema.TypedNode = (*_node)(nil)
@@ -52,12 +52,8 @@ func (w *_prototype) NewBuilder() ipld.NodeBuilder {
 	}}
 }
 
-// TODO: consider these Typed interfaces for the schema package
-
-type TypedPrototype interface {
-	ipld.NodePrototype
-
-	Representation() ipld.NodePrototype
+func (w *_prototype) Type() schema.Type {
+	return w.schemaType
 }
 
 func (w *_prototype) Representation() ipld.NodePrototype {

schema/typedNode.go

@@ -71,3 +71,16 @@ type TypedNode interface {
 type TypedLinkNode interface {
 	LinkTargetNodePrototype() ipld.NodePrototype
 }
+
+// TypedPrototype is a superset of the ipld.Nodeprototype interface, and has
+// additional behaviors, much like TypedNode for ipld.Node.
+type TypedPrototype interface {
+	ipld.NodePrototype
+
+	// Type returns a reference to the reified schema.Type value.
+	Type() Type
+
+	// Representation returns an ipld.NodePrototype for the representation
+	// form of the prototype.
+	Representation() ipld.NodePrototype
+}