[Haskell-beginners] Meaning of '!' in record defintion? UNPACK?

[Erik de Castro Lopo]

Hi all,

I'm looking at some code that defines a record:

    data Position = 
           Position { posOffset :: {-# UNPACK #-} !Int
                    , posRow :: {-# UNPACK #-} !Int
                    , posColumn :: {-# UNPACK #-} !Int
                    }

What does the the exclamation mark mean? And UNPACK?

Thanks in advance.

Cheers,
Erik
-- 
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Erik de Castro Lopo
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