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

Hi David, thank You for your suggestions but the usage of fclabes is much better for me (otherwise it uses template haskell inside too). Some benefits: - It has a nice example for usage. - Not even a little wrapper is needed to make a get (or set) with a record field. You can use the field name directly for both direction (get and set). - It's prepared for usage in a state monad. - A record field is represented with a value (and a type) so you can easily compose it (one of the main problem with haskell's original record field syntax). Thanks, Árpád On Tue, 2011-09-06 at 14:55 -0700, David Barbour wrote:

forgot to CC list.

---------- Forwarded message ---------- From: David Barbour Date: 2011/9/6 Subject: Re: [Haskell-cafe] Is there any way to parametrize a value update using record syntax? To: Poprádi Árpád

2011/9/6 Poprádi Árpád But it's ugly. Always the same, only the record selector has another name. Is it possible to generalize it?

You can generalize using template haskell. I believe Oleg's HList already provides such mechanisms, so you don't need to do this yourself. If you're doing this a lot, try the HList package. (If not, just do the

Also, I would say you've too tightly coupled your BigData to the MonadicEnv. I suggest you reduce it instead to:

setX :: X -> BigData -> BigData setX x' bd = bd { dataX = x' }

updX :: (X -> X) -> BigData -> BigData updX fx bd = bd { dataX = fx (dataX bd) }

Then in your state monad you can use: modify (setX x') gets dataX

And use of 'updX' is much more composable.

That aside, from personal experience, I'm usually okay just using: modify (\ s -> s { dataX = x' })

in the few places I need it.

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