You can write a generic 'is constructor' function using GHC Generics,
if you want:
{-# LANGUAGE
DeriveGeneric
, FlexibleContexts
, FlexibleInstances
, FunctionalDependencies
, MultiParamTypeClasses
, UndecidableInstances
#-}
import GHC.Generics
import Generics.Deriving.ConNames
class SameType a b | b -> a where
saturate :: b -> a
instance SameType a a where
saturate = id
instance SameType a b => SameType a (c -> b) where
saturate f = saturate (f undefined)
is :: (ConNames (Rep a), Generic a, SameType a b) => b -> a -> Bool
is ctor val = conNameOf val == conNameOf (saturate ctor)
Now you can do things like:
data Foo = A | B Int
deriving (Show, Generic)
*Main> is A A
True
*Main> is A (B 1)
False
*Main> is B A
False
*Main> is B (B 2)
True
Erik
On Mon, Jul 13, 2015 at 3:40 PM, Nikolay Amiantov
A nice idea! It can be helpful in some cases, although usually I have more complex patterns, for example "get all DataDefinitions from a list of TopLevelDefinitions parsed from a .hs file" or "filter all KeyPresses directed to a particular window from an Event stream".
On 07/13/2015 04:24 PM, Adam Bergmark wrote:
Perhaps this is of interest to you, http://hackage.haskell.org/package/generic-maybe
HTH, Adam
-- Nikolay. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe