eth/tracers: clean-up and comments

eth/tracers/native/call.go

@@ -13,7 +13,7 @@ import (
 )
 
 func init() {
-	Register("callTracerNative", NewCallTracer)
+	register("callTracerNative", NewCallTracer)
 }
 
 type callFrame struct {
@@ -33,7 +33,11 @@ type CallTracer struct {
 	callstack []callFrame
 }
 
+// NewCallTracer returns a native go tracer which tracks
+// call frames of a tx, and implements vm.Tracer.
 func NewCallTracer() Tracer {
+	// First callframe contains tx context info
+	// and is populated on start and end.
 	t := &CallTracer{callstack: make([]callFrame, 1)}
 	return t
 }

eth/tracers/native/native.go

@@ -6,19 +6,27 @@ import (
 	"github.com/ethereum/go-ethereum/core/vm"
 )
 
+// Tracer interface extends vm.Tracer and additionally
+// allows collecting the tracing result.
 type Tracer interface {
 	vm.Tracer
 	GetResult() (json.RawMessage, error)
 }
 
-type Constructor func() Tracer
+// constructor creates a new instance of a Tracer.
+type constructor func() Tracer
 
-var tracers map[string]Constructor = make(map[string]Constructor)
+var tracers map[string]constructor = make(map[string]constructor)
 
-func Register(name string, fn Constructor) {
+// register makes native tracers in this directory which adhere
+// to the `Tracer` interface available to the rest of the codebase.
+// It is typically invoked in the `init()` function.
+func register(name string, fn constructor) {
 	tracers[name] = fn
 }
 
+// New returns a new instance of a tracer, if one was
+// registered under the given name.
 func New(name string) (Tracer, bool) {
 	if fn, ok := tracers[name]; ok {
 		return fn(), true