Re: [Haskell-cafe] Is there any way to parametrize a value update using record syntax?

Hi Erik, thanks a lot! fclabels is an amazing package! My code become much clearer. Greetings, Árpád On Wed, 2011-09-07 at 00:04 +0200, Erik Hesselink wrote:

2011/9/6 Poprádi Árpád :

...

i have a record with a lot of items used in a state monad.

data BigData = BigData { data1 :: X , data2 :: X -- and so on }

updateData1 :: X -> MonadicEnv() updateData1 d = do; env <- get; put env {data1 = d}

updateData2 :: X -> MonadicEnv() updateData2 d = do; env <- get; put env {data2 = d}

But it's ugly. Always the same, only the record selector has another name. Is it possible to generalize it?

You can use the fclabels package [1] for this. It makes record labels first class, and also provides functions to update parts of a record in the state monad [2]. You would be able to write something like:

updateData1 = puts data1 d

It has a function for modifcation as well, which is even uglier with regular record syntax.

Erik

[1] http://hackage.haskell.org/package/fclabels [2] http://hackage.haskell.org/packages/archive/fclabels/1.0.4/doc/html/Data-Lab...