2009/11/5 Sebastiaan Visser
Hello all,
Wouldn't it be nice if we could write point free case statements?
I regularly find myself writing down something like this:
myFunc = anotherFunc $ \x -> case x of Left err -> print err Right msg -> putStrLn msg
We could really use a case statement in which we skip the scrutinee and make `(case of {})' be syntactic sugar for `(\x -> case x of {})'.
So we could write:
myFunc = anotherFunc $ case of Left err -> print err Right msg -> putStrLn msg
A minor syntactical addition, a big win!
Cheers,
-- Sebastiaan Visser _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Morten Rhiger implemented "Type-safe pattern combinators" [1], which are essentially a library for pattern matching, entirely within Haskell98. As an example, he implemented "anonymous pattern-matching" with this library, which is similar to what you ask for. It would be certainly be possible to implement your proposal with his library. My library "first-class-patterns" [2] on Hackage essentially follows Morten Rhiger's approach, but makes the types more understandable. I implemented point free case expressions (the 'elim' function) and monadic pattern matches (the 'mmatch' function) in version 0.2.0, which I just uploaded. For instance, you could write
import Data.Pattern
---- anonymous matching ex6 :: Show a => Either a String -> IO () ex6 = elim $ left var ->> print <|> right var ->> putStrLn
-- monadic matching ex8 :: IO () ex8 = mmatch getLine $ cst "" ->> return () <|> var ->> putStrLn . ("You said " ++)
Cheers, Reiner [1] http://www.itu.dk/people/mir/typesafepatterns.pdf [2] http://hackage.haskell.org/package/first-class-patterns