Personally I would like
{-# OPTIONS -fglasgow-exts -fgenerics -}
module Blog.Types where
family Usual = (Eq, Ord, Read, Show, Typeable)
data BlogEntry = Entry EpochSeconds Name Email Title Body deriving Usual
newtype Name = Name String deriving Usual
newtype Title = Title String deriving Usual
newtype Body = Body String deriving Usual
Of course, if you're doing that, you might as well change those last 3
lines with
newtype-schema NamedString = NamedString String deriving Usual
instantiate NamedString with Name, Title, Body
To me, that is very clear. Syntax-wise, I am sure things can be
improved (but I rather like 'family', 'foo-schema' and 'instantiate',
but not really the 'with').
Jacques
Alex Jacobson wrote:
Consider this module for a blog entry that I will want to put in
various generic collections that require Ord
{-# OPTIONS -fglasgow-exts #-}
module Blog.Types where
import Data.Typeable
import Data.Generics
data BlogEntry = Entry EpochSeconds Name Email Title Body
deriving (Eq,Ord,Read,Show,Typeable)
newtype Name = Name String deriving (Eq,Ord,Read,Show,Typeable)
newtype Title = Title String deriving (Eq,Ord,Read,Show,Typeable)
newtype Body = Body String deriving (Eq,Ord,Read,Show,Typeable)
It seems really unnecessarily verbose. Having to add the OPTION
header AND import Data.Typeable and Data.Generics just to derive
Typeable is a beat-down. It is even more of a beat-down to have to
add a deriving clause for every newtype to make this all work nicely.
Is there a way to make all types automatically derive everything
unless there is an explicit instance declaration otherwise?
{-# OPTIONS -fglasgow-exts -fgenerics -fderiving#-}
module Blog.Types where
data BlogEntry = Entry EpochSeconds Name Email Title Body
newtype Name = Name String newtype Title = Title String newtype
Body = Body String
Isn't that much nicer?
-Alex-
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