Pattern match multiple dates

According to this answer, I can match against DateTime.MinValue like this:

let result = 
  match date with 
  | d when d = DateTime.MinValue -> 1
  | _                            -> 0

How do I do this, if I have a match like this?

let result = 
  match (startDate, endDate) with 

This doesn’t work:

let result = 
  match (startDate, endDate) with 
  | d when d = DateTime.MinValue, e when e = DateTime.MinValue  -> 0

Compiler error for the second when:

Unexpected keyword 'when' in pattern matching. Expected '->' or other token.

>Solution :

when can be added to a whole pattern, not to nested patterns, so you need something like this:

match (startDate, endDate) with
| d, e when d = DateTime.MinValue && e = DateTime.MinValue -> 0
| _ -> 1

Note that in this case, pattern matching is not really necessary, and you can go for a simpler if:

if d = DateTime.MinValue && e = DateTime.MinValue then
    0
else
    1