On 02.10.2010, at 20:35, Henning Thielemann wrote:
On Sat, 2 Oct 2010, Colin Paul Adams wrote:
Prelude> (if then "Haskell" else "Cafe") False
Max> "Cafe"
My reaction is to ask:
Can you write this as:
(if then else) False "Haskell" "Cafe"
?
Sure:
ifThenElse :: Bool -> a -> a -> a
ifThenElse True x _ = x
ifThenElse False _ y = y
Prelude> ifThenElse False "Haskell" "Cafe"
You can use a similar approach for case expressions ; )
import Prelude hiding ( catch )
import System.IO.Unsafe ( unsafePerformIO )
import Control.Exception ( catch, evaluate, PatternMatchFail )
caseOf :: a -> [a -> b] -> b
caseOf x = unsafePerformIO . firstMatch . map ($x)
firstMatch :: [a] -> IO a
firstMatch (x:xs) = catch (evaluate x) (handlePatternFail (firstMatch
xs))
handlePatternFail :: a -> PatternMatchFail -> a
handlePatternFail x _ = x
test = (flip caseOf [\1 -> "One", \_ -> "Not-one"]) 1
Well, to tell the truth this does not work correctly as the following
example shows.
test2 = (flip caseOf [\1 -> ((\2 -> "One") 3), \_ -> "Not-one"]) 1
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
