(no subject)

[Ashley Yakeley]

At 2002-02-24 22:46, Tom Bevan wrote:

>I've come across this sort of data constructor below many times but I'm
>not really sure how to use it. Can someone please point me to the right
>section in the documentation?

http://haskell.org/onlinereport/decls.html#sect4.2.1
"Labelled Fields"

>In particular, I want to know how to create a calendar time and how to
>access the fields .
>
>Tom
>
>data CalendarTime = CalendarTime {
>		ctYear   :: Int,
>        	ctMonth  :: Month,
>        	ctDay, ctHour, ctMin, ctSec  :: Int,
>		ctPicosec :: Integer,
>		ctWDay    :: Day,
>		ctYDay       :: Int,
>		ctTZName   :: String,
>		ctTZ          :: Int,
>		ctIsDST :: Bool
>	} deriving (Eq, Ord, Read, Show)

Basically it's equivalent to this:

data CalendarTime = CalendarTime Int Month Int Int Int Int Integer Day 
Int String Int Bool deriving (Eq, Ord, Read, Show);

ctYear (CalendarTime x _ _ _ _ _ _ _ _ _ _ _) = x;
ctMonth (CalendarTime _ x _ _ _ _ _ _ _ _ _ _) = x;
ctDay (CalendarTime _ _ x _ _ _ _ _ _ _ _ _) = x;
etc.

...but you can also use the labelled fields to construct:

CalendarTime
    {
    ctYear = 2002,
    ctMonth = 2,
    ...
    }


-- 
Ashley Yakeley, Seattle WA