Time/Date range grammars

Question

I need to parse strings containing time spans such as:

• Thursday 6:30-7:30 AM
• December 30, 2009 - January 1, 2010
• 1/15/09, 7:30 to 8:30 PM
• Thursday, from 6:30 to 7:30 AM
• and others...

added

• 6:30 to 7:30

and date/times such as most any cases that Word's insert->date can generate

As I'd be extremely surprised if anything out there covers all the cases I need to cover, I'm looking for grammars to start from.

Answer 1

Ok, the following grammar parses anything in your example:

DTExp        = Day, ['-', Day]
Day          = DayExp, [[','], ['from'], TimeRange]
DayExp       = WeekDay
             | [Weekday], Month, DayNumber, [[','], YearNumber]
             | [Weekday], MonthNumber, '/', DayNumber, ['/', YearNumber]
TimeRange    = Time, [['-'|'to'] Time]
Time         = HourNumber, ':', MinuteNumber, ['AM'|'PM']
WeekDay      = 'monday' | 'tuesday' | ...
Month        = MonthNumber | MonthName
MonthName    = 'january' | 'february' | ...
DayNumber    = Number
MonthNumber  = Number
YearNumber   = Number, ['AD'|'BC']
HourNumber   = Number
MinuteNumber = Number

There is a slight problem in the grammar. If a DayExp is read, followed by a Time, and a '-', then you could expect another DayExp or another time. But this is solved by a lookahead, because if it is a time, a number is followed by a ':'.

Lets try to construct a parse tree:

Thursday  6    :  30     -   7    :   30    AM
    |     |        |         |         |     |
WeekDay Number : Number  - Number : Number   |
    |     -----|----         -----|----------- 
    |         Time       -       Time
    |           ---------|---------
 DayExp              TimeRange
    ----------|-----------
             Day
              |
            DTExp