gistfile1.diff

diff --git a/log/value.go b/log/value.go
index f2c55b7..ba622da 100644
--- a/log/value.go
+++ b/log/value.go
@@ -11,12 +11,10 @@ type Value interface{}
 
 // A Valuer generates a log value. When passed to With, it represents a
 // dynamic value which is re-evaluated with each log event.
-type Valuer interface {
-	// Value returns a log Value instead of an interface{} to avoid
-	// inadvertently matching types from packages not intended for use with
-	// gokit/log.
-	Value() Value
-}
+// It returns a log Value instead of an interface{} to avoid
+// inadvertently matching types from packages not intended for use with
+// gokit/log.
+type Valuer func() Value
 
 // BindValues returns a slice with all value elements (odd indexes) that
 // implement Valuer replaced with the result of calling their Value method. If
@@ -30,7 +28,7 @@ func BindValues(keyvals ...interface{}) []interface{} {
 	copy(bound, keyvals)
 	for i := 1; i < len(bound); i += 2 {
 		if v, ok := bound[i].(Valuer); ok {
-			bound[i] = v.Value()
+			bound[i] = v()
 		}
 	}
 
@@ -46,32 +44,28 @@ func containsValuer(keyvals []interface{}) bool {
 	return false
 }
 
-// Timestamp is a Valuer that invokes the underlying function when bound,
-// returning a time.Time. Users will probably want to use DefaultTimestamp or
-// DefaultTimestampUTC.
-type Timestamp func() time.Time
-
-// Value implements Valuer.
-func (t Timestamp) Value() Value { return t() }
-
-// Caller is a Valuer that returns a file and line from a specified depth in
-// the callstack. Users will probably want to use DefaultCaller.
-type Caller int
-
-// Value implements Valuer.
-func (c Caller) Value() Value { return stack.Caller(int(c)) }
-
 var (
+	// Timestamp returns a Valuer that invokes the underlying function when bound,
+	// returning a time.Time. Users will probably want to use DefaultTimestamp or
+	// DefaultTimestampUTC.
+	Timestamp = func(t func() time.Time) Valuer {
+		return func() Value { return t() }
+	}
 	// DefaultTimestamp is a Timestamp Valuer that returns the current wallclock
 	// time, respecting time zones, when bound.
-	DefaultTimestamp Timestamp = time.Now
-
+	DefaultTimestamp = Timestamp(time.Now)
 	// DefaultTimestampUTC wraps DefaultTimestamp but ensures the returned
 	// time is always in UTC. Note that it invokes DefaultTimestamp, and so
 	// reflects any changes to the DefaultTimestamp package global.
-	DefaultTimestampUTC Timestamp = func() time.Time { return DefaultTimestamp().UTC() }
-
+	DefaultTimestampUTC = Timestamp(func() time.Time {
+		return DefaultTimestamp().(time.Time).UTC()
+	})
+	// Caller is a Valuer that returns a file and line from a specified depth in
+	// the callstack. Users will probably want to use DefaultCaller.
+	Caller = func(depth int) Valuer {
+		return func() Value { return stack.Caller(depth) }
+	}
 	// DefaultCaller is a Valuer that returns the file and line where the Log
 	// method was invoked.
-	DefaultCaller = Caller(4)
+	DefaultCaller = Caller(3)
 )