All,
2013/3/13
So, Code is almost applicative. Almost -- because we only have a restricted pure: pureR :: Lift a => a -> Code a with a Lift constraint. Alas, this is not sufficient for realistic parsers, because often we have to lift functions, as in the example of parsing a pair of characters:
I've previously used an approach like this in the grammar-combinators library. See http://hackage.haskell.org/packages/archive/grammar-combinators/0.2.7/doc/ht... and http://hackage.haskell.org/packages/archive/grammar-combinators/0.2.7/doc/ht.... The approach uses a restricted pure like this: class ProductionRule p => LiftableProductionRule p where epsilonL :: a -> Q Exp -> p aSource and associated epsilonLS :: (Lift v, LiftableProductionRule p) => v -> p v epsilonLS v = epsilonL v $ lift v There is a function liftGrammar which lifts a grammar that uses the type class to a list of declarations using TH. This allowed me to start from a context-free grammar, transform it to a non-left-recursive grammar, optimize it and then lift it using TH. In some tests, I found that this improved performance significantly over using the transformed grammar directly, even when I try to force the transformation to happen before the benchmark. I assume this is because the lifted grammar is optimised better by the compiler. Regards, Dominique