NilTime -> nilTime

So users can not manipulate that variable

Also added some documentation

2 files changed, 15 insertions, 13 deletions

diff --git a/chronos/chronos.go b/chronos/chronos.go
index 18bf775..e66fc76 100644
--- a/chronos/chronos.go
+++ b/chronos/chronos.go
@@ -16,7 +16,7 @@ const (
 	Year
 )
 
-var NilTime time.Time
+var nilTime time.Time
 
 func (tu TimeUnit) String() string {
 	switch tu {
@@ -123,24 +123,26 @@ func (f Frequency) addTo(t time.Time, mul uint) time.Time {
 	case Year:
 		return time.Date(year+fq, month, day, hour, min, sec, 0, loc)
 	default:
-		return NilTime
+		return nilTime
 	}
 }
 
 func (f Frequency) minApprox() time.Duration { return time.Duration(f.Count) * f.Unit.minApprox() }
 func (f Frequency) maxApprox() time.Duration { return time.Duration(f.Count) * f.Unit.maxApprox() }
 
+// Chronos describes a time schedule. It has a start and optional end point and an optional frequency.
 type Chronos struct {
 	Start, End time.Time
 	Freq       Frequency
 }
 
+// NextAfter calculates the next time in the schedule after t. If no such time exists, nil is returned (test with Time.IsZero()).
 func (c Chronos) NextAfter(t time.Time) time.Time {
 	if !t.After(c.Start) {
 		return c.Start
 	}
 	if c.Freq.Count == 0 {
-		return NilTime
+		return nilTime
 	}
 
 	d := t.Sub(c.Start)
@@ -154,10 +156,10 @@ func (c Chronos) NextAfter(t time.Time) time.Time {
 			continue
 		}
 		if (!c.End.IsZero()) && t2.After(c.End) {
-			return NilTime
+			return nilTime
 		}
 		return t2
 	}
 
-	return NilTime // Should actually never happen...
+	return nilTime // Should actually never happen...
 }
diff --git a/chronos/chronos_test.go b/chronos/chronos_test.go
index 5efb7e9..692af14 100644
--- a/chronos/chronos_test.go
+++ b/chronos/chronos_test.go
@@ -18,14 +18,14 @@ func TestChronos(t *testing.T) {
 		now   time.Time
 		want  time.Time
 	}{
-		{mktime(1991, 4, 30, 0, 0), NilTime, Year, 1, mktime(2013, 8, 26, 13, 37), mktime(2014, 4, 30, 0, 0)},
-		{mktime(2013, 1, 1, 0, 0), NilTime, Year, 0, mktime(2013, 8, 26, 13, 37), NilTime},
-		{mktime(2013, 1, 1, 0, 0), NilTime, Year, 0, mktime(2012, 1, 1, 0, 0), mktime(2013, 1, 1, 0, 0)},
-		{mktime(1900, 12, 24, 12, 34), NilTime, Year, 5, mktime(2013, 8, 26, 13, 37), mktime(2015, 12, 24, 12, 34)},
-		{mktime(1900, 12, 24, 12, 34), mktime(2010, 1, 1, 1, 1), Year, 5, mktime(2013, 8, 26, 13, 37), NilTime},
-		{mktime(2013, 8, 1, 4, 2), NilTime, Week, 3, mktime(2013, 8, 26, 13, 37), mktime(2013, 9, 12, 4, 2)},
-		{mktime(2013, 8, 26, 13, 37), NilTime, Year, 0, mktime(2013, 8, 26, 13, 37), mktime(2013, 8, 26, 13, 37)},
-		{mktime(2013, 8, 25, 13, 37), NilTime, Day, 1, mktime(2013, 8, 26, 13, 37), mktime(2013, 8, 26, 13, 37)},
+		{mktime(1991, 4, 30, 0, 0), nilTime, Year, 1, mktime(2013, 8, 26, 13, 37), mktime(2014, 4, 30, 0, 0)},
+		{mktime(2013, 1, 1, 0, 0), nilTime, Year, 0, mktime(2013, 8, 26, 13, 37), nilTime},
+		{mktime(2013, 1, 1, 0, 0), nilTime, Year, 0, mktime(2012, 1, 1, 0, 0), mktime(2013, 1, 1, 0, 0)},
+		{mktime(1900, 12, 24, 12, 34), nilTime, Year, 5, mktime(2013, 8, 26, 13, 37), mktime(2015, 12, 24, 12, 34)},
+		{mktime(1900, 12, 24, 12, 34), mktime(2010, 1, 1, 1, 1), Year, 5, mktime(2013, 8, 26, 13, 37), nilTime},
+		{mktime(2013, 8, 1, 4, 2), nilTime, Week, 3, mktime(2013, 8, 26, 13, 37), mktime(2013, 9, 12, 4, 2)},
+		{mktime(2013, 8, 26, 13, 37), nilTime, Year, 0, mktime(2013, 8, 26, 13, 37), mktime(2013, 8, 26, 13, 37)},
+		{mktime(2013, 8, 25, 13, 37), nilTime, Day, 1, mktime(2013, 8, 26, 13, 37), mktime(2013, 8, 26, 13, 37)},
 	}
 
 	for i, e := range tbl {