[Haskell-beginners] iterating over a range of dates

[Alexander Dunlap]

On 9 July 2011 09:33, Rolf Hanson <rolf.hanson at gmail.com> wrote:
> Hi, I'm trying to iterate over a range of dates and print them out.
> Here's how I am doing it in Ruby:
>
> 'require 'date'
>
> now      = Date.parse('2011-07-11')
> end_date = Date.parse('2011-12-31')
>
> (now..end_date).each do |d|
>  # print out a date that looks like:
>  # Monday, July 11, 2011
>  puts "#{d.strftime('%A, %B %d, %Y')}"
> end
>
> I've been looking at the docs for Data.Time.Format and Data.Time.Calendar and am a bit puzzled at where to begin. Anyone have ideas? I've not found many (any?) examples of time and date manipulation in Haskell.
>
> RW
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A good starting point would be the Enum instance of Day in
Data.Time.Calendar, which lets you use the [a..b] syntactic sugar to
do a range. fromGregorian will get you from a year, month, and day to
the Day type:

Prelude Data.Time.Calendar> [fromGregorian 2011 07 09..fromGregorian 2011 07 20]
[2011-07-09,2011-07-10,2011-07-11,2011-07-12,2011-07-13,2011-07-14,2011-07-15,2011-07-16,2011-07-17,2011-07-18,2011-07-19,2011-07-20]

This is equivalent to

enumFromTo (fromGregorian 2011 07 09) (fromGregorian 2011 07 20)

formatTime in Data.Time.Format will probably get you the rest of the way.

Hope that helps,
Alex