Document new cal-day.

doc/calendar.md

@@ -22,6 +22,8 @@ with calendar dates - mostly with month granularity.
 
 ### Month
 
+    (import cal-month)
+
 Module for handling months algebra to be used in period construction
 and matching.
 
@@ -136,6 +138,8 @@ Returns a new valid month that comes ```n``` months after ```m```. If
 
 ### Period
 
+    (import cal-period)
+
 This module implements simple calendar period handling with month
 granularity. The period contains fields ```since``` which is the first
 month of the period and ```before``` which is the first month just
@@ -261,3 +265,71 @@ If ```v``` is a valid month, returns it unchanged. If it is a day,
 uses ```cal-day->month``` for conversion with given ```stop?``` as
 second argument.
 
+### Day
+
+    (import cal-day)
+
+This module encapsulates date storage with daily granularity.
+
+    (make-cal-day y m d)
+
+* ```y``` - valid year (1000-9999)
+* ```m``` - valid month number (1-12)
+* ```d``` - valid day number (1-31)
+
+Construct a new cal-day structure representing a single calendar day.
+
+    (cal-day? v)
+
+* ```v``` - any value
+
+Return ```#t``` if given value is a cal-day structure and it
+represents a valid day, ```#f``` otherwise.
+
+    (cal-day-year d)
+
+* ```d``` - valid cal-day structure
+
+Returns the year field of the structure.
+
+    (cal-day-month d)
+
+* ```d``` - valid cal-day structure
+
+Returns the month field of the structure.
+
+    (cal-day-day d)
+
+* ```d``` - valid cal-day structure
+
+Returns the day field of the structure.
+
+    (cal-day->month d [stop?])
+
+* ```d``` - a valid cal-day structure
+* ```stop?``` - if ```#t```, conversion for period end
+
+Converts given cal-day to cal-month. If ```stop?``` is ```#f```, it
+just strips the day number. Otherwise it converts the day to the same
+month only if it is the first day of the month. It converts to the
+next calendar month otherwise.
+
+    (cal-day->string d)
+
+* ```d``` - a valid cal-day structure
+
+Converts given day into "YYYY-MM-DD" ISO string representation.
+
+    (string->cal-day s)
+
+* ```s``` - a string containing "YYYY-MM-DD" ISO date
+
+Parses the string and returns a valid cal-day structure.
+
+    (parse-cal-day/month s)
+
+* ```s``` - a string with ISO date with optional day part
+
+Tries parsing the string as cal-day and returns the result upon
+success. Upon failure, parses the string as cal-month.
+