Hello Tom, Thursday, May 4, 2006, 5:20:54 PM, you wrote:
I was experimenting with records this morning and discovered a slight oddity...
data Rec = RecA { a :: Int } | RecB { a :: Int, b :: Bool } deriving Show
main :: IO () main = do print (b (RecB { a = 1, b = True })) -- Works print (b (RecA { a = 1 })) -- Doesn't
Of course extracting "b" from a record constructed with "RecA" is illegal, but the compiler did not warn against it (ghc -W). I was expecting a warning similar to non-exhaustive pattern matching.
Are records with optional fields really type safe?
it shpuld be a runtime check. seems that Haskell is so changed your mind that you expect that compiler should check anything at compile time :) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com