Today I noticed that GHC is more concerned (when using -Wall) about
uninitialized fields when those fields have names:
data A = A {a::Integer}
data B = B Integer
x :: A
x = A{} -- Gives a nice warning: "Fields of `A' not initialised: a"
y :: B
y = B{} -- No warning!
Is this on purpose? If so, what is the rationale?
The context in which I encountered this boils down to the following:
{-# LANGUAGE RecordWildCards #-}
data C = C {c::Integer}
f :: C -> C
f C{..} = C{..}
g :: C -> Integer
g (C i) = i
main :: IO ()
main = print (g (f (C 3)))
This code worked fine (and printed "3"), until I made C's Integer
nameless. This made it crash with following runtime error instead:
T: T.hs:6:11-15: Missing field in record construction
The crash and error are perfectly understandable, but it would have been
more helpful if GHC had warned about this at compile-time! The reason it
didn't, though, is because of its aforementioned cavalier attitude
towards uninitialized fields that don't have names... :-)
(I'm using GHC 7.0.4.)
Cheers,
Eelis
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
