Move ops.SentinelError to types.SentinelError

This feel better than having different packages depend on the ops
package just for the SentinelError definition.

db/database.go

@@ -3,7 +3,6 @@ package db
 import (
 	"context"
 
-	"github.com/mbland/elistman/ops"
 	"github.com/mbland/elistman/types"
 )
 
@@ -20,7 +19,7 @@ type Database interface {
 //
 // Database.Get returns this error when the underlying database request
 // succeeded, but there was no such Subscriber.
-const ErrSubscriberNotFound = ops.SentinelError("is not a subscriber")
+const ErrSubscriberNotFound = types.SentinelError("is not a subscriber")
 
 // A SubscriberProcessor performs an operation on a Subscriber.
 //

handler/parser.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/google/uuid"
 	"github.com/mbland/elistman/ops"
+	"github.com/mbland/elistman/types"
 )
 
 //go:generate go run golang.org/x/tools/cmd/stringer -type=eventOperationType
@@ -57,7 +58,7 @@ type ParseError struct {
 
 // Inspired by the example from the "Customizing error tests with Is and As
 // methods" section of https://go.dev/blog/go1.13-errors.
-const ErrUserInput = ops.SentinelError("invalid user input")
+const ErrUserInput = types.SentinelError("invalid user input")
 
 func (e *ParseError) Error() string {
 	return e.Type.String() + ": " + e.Message

ops/errors.go

@@ -1,17 +1,9 @@
 package ops
 
-// SentinelError is type for defining constant error values.
-//
-// Inspired by: https://dave.cheney.net/2019/06/10/constant-time
-type SentinelError string
-
-// Error returns the string value of a SentinelError.
-func (e SentinelError) Error() string {
-	return string(e)
-}
+import "github.com/mbland/elistman/types"
 
 // ErrExternal indicates that a request to an upstream service failed.
 //
 // handler.Handler checks for this error in order to return an HTTP 502 when
 // applicable.
-const ErrExternal = SentinelError("external error")
+const ErrExternal = types.SentinelError("external error")

types/errors.go

@@ -0,0 +1,11 @@
+package types
+
+// SentinelError is type for defining constant error values.
+//
+// Inspired by: https://dave.cheney.net/2019/06/10/constant-time
+type SentinelError string
+
+// Error returns the string value of a SentinelError.
+func (e SentinelError) Error() string {
+	return string(e)
+}