One of the most common complaints heard about Haskell is that Data.Time is so much more difficult to use than the basic time API in most other languages. I believe that those complaints are totally unjustified. It's
Getting off the subject, but: I think if the complaint is that it's hard because it doesn't have much documentation, as it is for me, then the complaint is totally justified. Data.Time has no documentation, so right off you have to start guessing about which module to use. It took me a long time to figure out that a plain yyyy/mm/dd is modeled as a Data.Time.Calendar.Day. Or is it JulianDay? What's an OrdinalDate? MonthDay sounds promising but defines no data types. The haddock talks about Julian days and "proleptic Gregorian calendars" and never quite gets around to mentioning that this is not just for people wanting to calculate how many days there are between now and the assassination of Julius Caesar, but for anyone wanting to deal with a modern date. Most people, when looking for "a date" are not going to start looking for things that say "julian day" on them. After wading through all this stuff that has no explanation but by function name sounds like it's for scholars of Christian antiquity, the temptation to go back to System.Time, which provides only one module and a totally straightforward pair of types, is really strong. Especially when System.Time says "this is deprecated" but doesn't say why. It must have been written for a scholar of Christian antiquity for other scholars of Christian antiquity who are disappointed that System.Time lacks functions to find the Paschal full moon of the Easter feast day of the Western Orthodox Catholic tradition as standardized by Pope XXXIV but not put into effect until... Say someone who understands Data.Time wrote some top level haddock and some examples of how to create dates, create times, get the current date and time, and find the number of months and days between now and then along with some of the things to take into account, etc. Perhaps the majority of the complaints would be satisfied. I don't know enough about dates to write the intro, but I'd be happy to proofread one.