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?
-Tom
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