Serguey Zefirov writes:

2010/10/27 Andy Stewart :

...

Hi all,

I want use TH write some function like below:

 data DataType = StringT                | IntT                | CharT

 parse :: [(String,DataType)] -> (TypeA, TypeB, ... TypeN)

Example:

 parse [("string", StringT), ("001", IntT), ("c", CharT)]

will return:

 ("string", 001, 'c')

So how to use TH write 'parse' function?

I think that you should use TH properly, without compiler and logical errors.

What actually do you want? I'm build multi-processes communication program.

Example i have two processes : Client and Server. At Client side, i pass [DataType] to Server, example: [StringT, IntT, CharT] Server will handle "user input" with [DataType] and return result [String] to Client side, example: ["string", "001", "c"] Then at Client side, i need parse [String] to get real value: ("string", 001, 'c') Because, [DataType] have many different case, so i want pass [String] between processes, and use TH parse result [String] at Client side. Thanks, -- Andy

2010/10/27 Andy Stewart :

Serguey Zefirov writes:

...

I think that you should use TH properly, without compiler and logical errors.

What actually do you want? I'm build multi-processes communication program.

You don't need TH here, I think. You can write a class Ask: class Ask a where ask :: YourMonad a and then instance it: instance Ask Int where ask = liftIO $ do { putStrLn "Enter integer:"; l <- getLine; return $ read l} instance Ask Char where ask = liftIO $ do { putStrLn "Enter char:"; l <- getLine; return $ head l} instance Ask String where ask = liftIO $ do { putStrLn "Enter string:"; l <- getLine; return l} instance (Ask a, Ask b, Ask c) => Ask (a,b,c) where ask = liftIO $ do { a <- ask; b <- ask; c <- ask; return (a,b,c)} You can pass ask values between processes, receiving results of asking. TH is great and good, but it is that only when you absolutely exhausted of usual Haskell options.