[Haskell-cafe] "Casting" newtype to base type?

[Vlatko Basic]

-------- Original Message  --------
Subject: Re: [Haskell-cafe] "Casting" newtype to base type?
From: Tom Ellis <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk>
To: haskell-cafe at haskell.org
Date: 02.07.2013 15:25

> On Tue, Jul 02, 2013 at 03:03:08PM +0200, Vlatko Basic wrote:
>> Is there a nicer way to extract the 'IO String' from 'IOS',
>> without 'case' or without pattern matching the whole 'P'?
>>
>> newtype IOS = IOS (IO String)
>> data P = P {
>>    getA :: String,
>>    getB :: String,
>>    getC :: IOS
>>    } deriving (Show, Eq)
>>
>>
>> getC_IO :: P -> IO String
>> getC_IO p =
>>    case getC p of
>>      IOS a -> a
>> getC_IO (P _ _ (IOS a)) = a
>
> How about
>
>      unIOS :: IOS -> IO String
>      unIOS (IOS a) = a
>
>      getC_IO :: P -> IO String
>      getC_IO = unIOS . getC
>
Thanks for your answer.
I had those two funcs, but thought there might be a shorter/prettier one-func 
one-liner. :-)

> Tom
>
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