template-haskell

I have a datatype newtype Zq q = Zq (IntType q) where 'q' will be an instance of the class class Foo a where type IntType a and 'IntType' is just the underlying representation (i.e. Int, Integral, etc) associated with 'q'. I want to make Zq an instance of Data.Vector.Unbox . We are currently manually deriving Unbox using about 50 lines of trivial code as suggested in the link above. We will be making several different types 'Unbox' in our code, so writing 50 lines for each type is not appealing. I found two alternatives here . One alternative is to use this package which uses Template Haskell

I'm making a small package that defines wrappers for tuples and adds instances form them, like newtype Tuple2 a = Tuple2 { untuple2 :: (a, a) } deriving (...) tuple2 :: a -> a -> Tuple2 a tuple2 = ... instance Traversable Tuple2 where ... instance Foldable Tuple2 where ... instance Functor Tuple2 where ... instance Applicative Tuple2 where ... This repeats from 2 to 15 , so it looks like a job for Template Haskell. The generated code is always Haskell 98 compatible, so I'd like the final result to be a Haskell 98 compatible package too. Is it possible to generate a piece of code using Template

I am writing a simple HashString class, which is just a string and its hash: data HashString = HashString Int -- ^ hash T.Text -- ^ string! Now I'm trying to generate these at compile time with something like: $(hString "hello, world") :: HashString I want the hash, and the text packing to happen at compile time. How do I do this? Here's what I've tried so far, but I'm not sure if its right, nor am I sure it does everything at compile time: hString :: String -> Q Exp hString s = [| HashString (hash $ T.pack s) (T.pack s) |] The way you've written your code, no evaluation will happen at compile

I'm trying to learn some Template Haskell. As an exercise, I wrote a function that can generate things like isLeft and isRight (inspired by this question ). Here's my humble attempt: isA connam = do ConE nam <- connam nn <- newName "p" lamE [varP nn] $ caseE (varE nn) [ match (conP nam [wildP]) ( normalB [| True |] ) [], match wildP ( normalB [| False |] ) [] ] The problem is that I have to write $(isA [| Left |]) instead of the more intuitive isA Left . Is it possible to get rid of the ugly syntax? I can't seem to find the answer in the documentation. The function only works with one-argument

The documentation for Safe Haskell states: [...] Unfortunately Template Haskell can be used to subvert module boundaries and so could be used gain access to this constructor. [...] The use of the -XSafe flag to compile the Danger module restricts the features of Haskell that can be used to a safe subset. This includes disallowing unsafePerfromIO, Template Haskell,[...] Used as a macro system that translates an AST to another AST, should it not be possible to simply restrict TH to the safe subset of Haskell, and also restrict the resulting AST to this subset? A bit further down on the page you

I'm trying to create the ring Z/n (like normal arithmetic, but modulo some integer). An example instance is Z4: instance Additive.C Z4 where zero = Z4 0 (Z4 x) + (Z4 y) = Z4 $ (x + y) `mod` 4 And so on for the ring. I'd like to be able to quickly generate these things, and I think the way to do it is with template haskell. Ideally I'd like to just go $(makeZ 4) and have it spit out the code for Z4 like I defined above. I'm having a lot of trouble with this though. When I do genData n = [d| data $n = $n Integer] I get "parse error in data/newtype declaration". It does work if I don't use