Hello café, I have a little DSL in my program as follow. Now I'd like to add a Map constructor in it. Thats where I would need help!
> data Obs a where > AllPlayers :: Obs [Int] > Plus :: (Num a) => Obs a -> Obs a -> Obs a > And :: Obs Bool -> Obs Bool -> Obs Bool > Vote :: Obs String -> Obs Int -> Obs Bool > *Map :: (Obs a -> Obs b) -> Obs [a] -> Obs [b]* > -- and others Here is the evaluator for Obs: > evalObs :: Obs a -> Evaluator a > evalObs (Konst a) = return $ pure a > evalObs (Not a) = liftE not (evalObs a) > evalObs (Plus a b) = liftE2 (+) (evalObs a) (evalObs b) > evalObs (Minus a b) = liftE2 (-) (evalObs a) (evalObs b) > evalObs (Time a b) = liftE2 (*) (evalObs a) (evalObs b) > evalObs (And a b) = liftE2 (&&) (evalObs a) (evalObs b) > evalObs (Or a b) = liftE2 (||) (evalObs a) (evalObs b) > evalObs (Equ a b) = liftE2 (==) (evalObs a) (evalObs b) > evalObs (If a b c) = liftE3 (if3) (evalObs a) (evalObs b) (evalObs c) How you can see it is quite neat... But how can I write the evaluator for Map? Actually I have some half baked solution, 15 lines long that I don't dare to show ;) Actually compiling code excerpt is here: http://hpaste.org/40897/map_contstructor_in_a_dsl Thanks for your help. Corentin Below is some helper code: type Evaluator a = StateT Game Comm a (Either Actions a) -- | Combined lifters for Evaluator liftE = liftM . liftA liftE2 = liftM2 . liftA2 liftE3 = liftM3 . liftA3 instance Applicative (Either Actions) where pure x = Right x (Right f) <*> (Right x) = Right $ f x (Right _) <*> (Left u) = Left u (Left u) <*> (Right _) = Left u (Left u) <*> (Left v) = Left $ u ++ v
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