Hello Cafe!
I had a (simplified) record
data P = P {
a :: String,
b :: String,
c :: IO String
} deriving (Show, Eq)
but to get automatic deriving of 'Show' and 'Eq' for 'data P' I have created
'newtype IOS' and its 'Show' and 'Eq' instances
newtype IOS = IO String
instance Show (IOS) where show _ = "(IO String) function"
instance Eq (IOS) where _ == _ = True
(the easiest 'instance Show (IO String) where ...' produces "orphan instance")
and changed 'data P' to
data P = P {
a :: String,
b :: String,
c :: IOS
} deriving (Show, Eq)
but now when I try to set 'c' field in
fun :: FilePath -> P -> IO P
fun path p = do
b <- doesFileExist path
...
return $ p {c = readFile path}
I get error
Couldn't match expected type `IOS' with actual type `IO String'
which is correct.
So, the question is:
Is it possible to somehow "cast" 'IO String' to 'IOS',
or in some other way set 'c' field to an 'IO String' function
so that it can be later used such as 'content <- c p'.
Thanks
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