recursion-schemes package might do the trick. I wrote TH for it and somebody took care of getting it merged in. It should simplify some of this boilerplate.
I am looking for a solution to get rid of this silly boilerplate:
eval :: Ord var => Map var Bool -> Proposition var -> Bool eval ctx prop = evalP $ fmap (ctx Map.!) prop where evalP = \case Var b -> b Not q -> not $ evalP q And p q -> evalP p && evalP q Or p q -> evalP p || evalP q If p q -> evalP p ==> evalP q Iff p q -> evalP p == evalP q
What I would like to do in essence is to replace the data constructors like so:
-- Not valid Haskell!! Can't pattern match on constructor only... magic = \case Var -> id Not -> not And -> (&&) Or -> (||) If -> (==>) Iff -> (==)
compile = transformAST magic $ fmap (\case 'P' -> False; 'Q' -> True)
compile (Iff (Not (And (Var 'P') (Var 'Q'))) (Or (Not (Var 'P')) (Not (Var 'Q')))) ((==) (not ((&&) (id True) (id False))) ((||) (not (id True)) (not (id False))))
Note how the compiled expression exactly mirrors the AST, so there should be some meta programming technique for this.
Does anyone have an idea how I can achieve this?
The full source code is here: https://gist.github.com/vimuel/7dcb8a9f1d2b7b72f020d66ec4157d7b